Epoxy

UNDERSTANDING
EPOXY

JANUARY 2000

Table of Contents

Introduction .............................................................................................................................................................. 2
Chemistry .............................................................................................................................................................. 2-4

Industrial Formulators’ Epoxies ................................................................................................................. 4-5
Safety and Handling ............................................................................................................................................ 5
Measuring and Mixing Epoxy Systems ................................................................................................. 6-7

Techniques of Epoxy Use .............................................................................................................................. 7-8
Coating with Epoxy Resin ............................................................................................................................ 8-9
Fiberglassing with Epoxy Resin ............................................................................................................. 9-11

Using Fillers with Epoxy Resins .......................................................................................................... 12-13
Epoxy Resins as Strustural Adhesives ............................................................................................. 13-14
Filleting, Fairing and Molding with Epoxy Resins ..................................................................... 15-16

Painting and Finishing ............................................................................................................................. 16-17
Troubleshooting ................................................................................................................................................... 17

Introduction about the use of these products as outlined
in this booklet is a distillation of the knowl-
When you begin to work with epoxy resins, edge we have gained over the years. This is
it’s always useful to know a little of their to help you, the user, to be in charge. Your
history. The dictionary defines epoxy as responsibility is to make sure that all the
“heat setting resin made by the chemical products you use, including ours, are used
bonding of smaller molecules into larger properly. The section on chemistry may
ones.” seem a bit of a mystery to some of you, but
a rudimentary understanding will help you
While that may be over simplifying things a complete your tasks more efficiently.
little, in all epoxies, that is basically what is
happening. What becomes complicated is You’ll find here sections on basic chemistry
the thousands of variations that make each and safety regarding all epoxies. Proper
chemical compound used in the manufacture measuring and mixing techniques are next.
of epoxy resin formulations specifically And we finish with a useful section on
different to perform the job it was designed troubleshooting.
to do.

Scientists have been aware of epoxy resins Chemistry
for many years but the first commercial
exploration of their properties was undertaken A thorough knowledge of epoxy resin
in the 1930’s. This was in Germany by the chemistry is not necessary before you start,
firm of I.G. Farben Industries. However, it but having a basic chemical knowledge
was not until the 1950’s that use of the will help you complete your project more
compounds in a commercial way was effectively.
introduced in North America. At about this
time the founder of Industrial Formulators, The resin that is the basis for most of our
Jim Peters B.Sc., began experimenting with epoxy formulations is the diglycidol ether
them and over the years became one of the of bisphenol A (DGEBA). Bisphenol A is
leading formulators in the world. produced by reacting phenol with acetone
under suitable conditions. Bis means two,
Epoxies are among the “thermoset” family phenyl means phenol groups and the “A”
of resins, along with polyester, silicones, stands for acetone. Thus, bisphenol A is the
urethanes, melamines, acrylics and phenolics. chemical product made from chemically
Once curing of epoxies has taken place combining two phenols with one acetone.
they cannot be melted by heat. This makes Unreacted acetone and phenol are stripped
epoxies the opposite of such other plastics from the bisphenol A which is then reacted
(thermoplastics) like polyethylene, vinyl, with a material called epichlorohydrin. This
polypropylene, etc., which can be melted reaction sticks the two (di) glycidyl groups
and solidified over and over again. on ends of the bisphenol A molecule. The
resultant product is the diglycidyl ether of
Industrial Formulators, Inc. supplies epoxies bisphenyl A, or the basic epoxy resin. It is
for industries such as construction, electronics, these glycidyl groups that react with the
marine, automotive, sporting goods and amine hydrogen atoms on hardeners to
hobbies. Our epoxy formulations have been produce the cured epoxy resin.
used to solve problems and are used regularly
in pulp mills, submarines, dams, museums, Basic epoxy resin is very viscous and
railroads and research labs along with more unsuitable for use except as a thick glue
standard uses like boat building and electrical for specialized applications. At Industrial
potting. We are experimenting with new Formulators Inc., we purchase the material
uses for epoxy resins all the time. in this basic form, then modify it using
formulae developed by us. The result is
Our responsibility is to provide quality the various epoxy resin systems we offer.
products to our customers. The information

2

Hardeners used with room temperature that can accommodate one, or by changing
cured epoxy resins are most commonly the temperature and mass of the resin/
polyamines. That is, they are organic hardener mix.
molecules containing two or more amine
groups. Amine groups are not unlike ammonia The epoxy curing reaction is exothermic.
in structure except that they are attached to This means that it gives off heat as it cures.
organic molecules. Like ammonia, amines The rate at which the epoxy resin cures is
are strongly alkaline. Because of this similarity, dependent upon the curing temperature.
epoxy resin hardeners often have an ammonia- The warmer it is the faster it goes. The curing
like odor, most notable in the dead air space rate will vary by about half or double with
in containers right after they are opened. each 10°C (18°F) change in temperature.
Once in the open this odor is difficult to
detect because of the low vapor pressure For example, if an epoxy system takes 3 hours
of the polyamines. to become tack free at 21°C (70°F), it will be
tack free in 1.5 hours at 31°C (88°F) or tack
Reactive amine groups are nitrogen atoms free in 6 hours at 11°C (52F). Everything to
with one or two hydrogen atoms attached do with the speed of the reaction follows this
to the nitrogen. These hydrogen atoms react general rule. Pot life and working time are
with oxygen atoms from glycidol groups on greatly influenced by the initial temperature
the epoxy to form the cured resin - a highly of the mixed resin and hardener.
crosslinked thermoset plastic. Heat will
soften, but not melt a cured epoxy. The The gel time of the resin is the time it takes
three-dimensional structure gives the for a given mass held in a compact volume
cured resin excellent physical properties. to solidify. Gel time depends on the initial
temperature of the mass and follows the
The ratio of the glycidol oxygens to the above rule. Cure time is surface area/mass
amine hydrogens, taking into account the sensitive in addition to being temperature
various molecular weights and densities sensitive.
involved, determines the final resin to
hardener ratio. Varying the recommended What’s happening is this: as the reaction
ratio will leave either unreacted oxygen or proceeds it gives off heat. If the heat generated
hydrogen atoms depending upon which is immediately dissipated to the environment
side is in excess. The resultant cured resin (as occurs in thin films) the temperature of
will have lower strength, as it is not as the curing resin does not rise and the
completely crosslinked. reaction speed proceeds at a uniform pace.
If the resin is confined (as in a mixing pot)
Epoxy hardeners are not catalysts. Catalysts the exothermic reaction raises the temperature
promote reactions but do not chemically of the mixture, accelerating the reaction.
become a part of the finished product. Epoxy
hardeners mate with the epoxy resin, greatly Working time is about 75% of the gel time
contributing to the ultimate properties of the for the size and shape of the pot. It can be
cured system. lengthened by increasing the surface area
or working with a smaller batch. Material
Cure time of an epoxy system is dependent left in the pot will increase in absolute
upon the reactivity of the amine hydrogen viscosity measured at 24°C (75°F), for
atoms. While the attached organic molecule example, due to polymerization but initially
takes no direct part in the chemical reaction, decrease in apparent viscosity due to
it does influence how readily the amine heating. Material left in the pot to 75% of gel
hydrogen atoms leave the nitrogen and react time may appear quite thin (due to heating)
with the glycidol oxygen atom. Thus, cure but will actually be quite thick when cooled
time is set by the kinetics of the particular to room temperature. Thick, partially cured
amine used in the hardener. Cure time can epoxy is not as effective in wetting out
be altered only by selecting a different fiberglass cloth and bonding surfaces.
hardener, adding an accelerator in systems Experienced users either mix batches that

3

will be applied almost immediately or exposure will induce chalking and eventually
increase the surface area to slow the reaction, the epoxy will disintegrate, losing its
thus increasing working time. mechanical properties. The solution to
this problem is to protect the epoxy coating
Although the cure rate of an epoxy is with paint or with a varnish which contains
dependent upon temperature, the curing an ultraviolet light shield.
mechanism is independent of temperature.
The reaction proceeds most quickly in the Caution must be observed when using
liquid state. As the cure proceeds the system epoxy resins along with polyester resins.
changes from a liquid to a sticky viscous soft Observe the general rule that epoxy resins
gel. After gelation the reaction speed slows may be applied over cured polyesters that
down as hardness increases. Chemical have been dewaxed and well-sanded but
reactions proceed more slowly in the solid polyesters should never be used over cured
state. From the soft sticky gel the system epoxy resins. Unreacted amine in the epoxy
gets harder, slowly losing its stickiness. inhibits the peroxide catalyst in the polyester
It becomes tack free and continues to causing an incomplete cure at the interface.
become harder and stronger as time passes. Sanding does not get rid of the unreacted
amine. The result is a poor bond even
At normal temperatures the system will though the surface appears cured.
reach about 60 to 80% of ultimate strength Debonding will be the inevitable result.
after 24 hours. Curing then proceeds slowly
over the next several weeks, finally reaching
a point where no further curing will occur
without a significant increase in temperature.
Industrial Formulators’
However, for most purposes, room temperature Epoxies
cured systems can be considered fully cured
after 72 hours at 25°C (77°F). Industrial Formulators’ epoxies are formu-
lated systems, meaning that we start with
It is usually more efficient to work with as basic epoxy resins manufactured by large
fast a cure time as practical for the application chemical companies and modify them to
at hand. This allows the builder to get along make them suitable for the required end use.
to the next phase without wasting time In the first modification (for most products)
waiting for epoxy to cure. Faster curing films we reduce the viscosity by the addition of
with shorter tack times will have less chance diluents or low viscosity solvents, which are
to pick up fly tracks, bugs, and other airborne also epoxies. This makes an epoxy system
contaminants. thin enough to wet fiberglass cloth, coat
wood and bind various fillers to produce gap
A surface film may form in some epoxy systems filling glues and putties. Because the
during the curing process. Technically, this diluents we use are also epoxies, they are
surface film is an amine carbamate that can called reactive diluents, reacting with the
form in the presence of carbon dioxide and amines the same way the basic resin reacts,
water vapor. More appears on cool damp becoming a part of the cured
days than on warm sunny days. This film system. Other materials protect against long
is water-soluble and should be removed term embrittlement and im-
with soap and water before sanding and prove resiliency and impact resistance.
re-coating or painting. This occurs mainly Finally, trace materials designed to lower
when using 51-Cure or Cold Cure with surface tension, promote substrate wet
Jet Cure Hardener. All epoxies should be out, reduce cratering and “fisheye” forma-
sanded lightly but thoroughly before tion, aid in breaking bubbles and detraining
recoating, or recoated within 72 hours. air are used to produce the finished product.

Unprotected exterior epoxy resin coatings These modifications are what make our epoxy
are not ultimately sunlight resistant. After systems unique and different from others.
about six months of exposure to intense We develop the chemical formulations for our
sunlight they begin to degrade. Additional epoxy resins and hardeners. To ensure our

4

desired level of quality, all of our epoxy Keep Epoxy Resins and Hardeners off your skin
products are produced in our manufacturing Wear disposable gloves or barrier skin creams
facility. Every batch gets tested for both gel (available from Industrial Formulators Inc.)
time and “thin film set time”. Nothing is when working with epoxy resins. Never use
shipped to a customer that does not meet solvents to remove epoxies from your skin.
our high standards. Everything we ship Solvents, in addition to having problems that
cures if properly measured and thoroughly are as bad or worse than epoxies, can help
mixed. drive the hazardous ingredients into your
body. If accidental contact occurs, use a
The diverse background of our staff gives good handsoap and lots of water and paper
us the unique advantage of knowing and towels to remove epoxy from your skin.
applying epoxy technology far better than Then apply a good medicated skin cream
others in the business. The development, to replace the natural oils removed by the
manufacture, and distribution of Industrial handsoap. Using a solvent to remove
Formulators products is our only business, partially cured epoxy from your body is
and our staff takes pride in being personally not an acceptable alternative.
available to all of our customers.
If a rash develops when working with
The dominant factor in the design, develop- epoxies you should stop until it clears up.
ment, and evolution of Industrial Formulators If the rash is bad or persists see a doctor.
products has been this: Take him a copy of this book and have him
An Epoxy System should adapt to the conditions of contact us if he needs additional information.
Don’t continue to work with epoxy if you
the user - Not the other way around. break out every time you get near it. This
is your body’s way of telling you to cool it.
Pay attention.
Safety and Handling
Working cleanly and keeping epoxy off you
We select our resin and hardener raw are the keystones of epoxy safety. Work in a
materials with the health and safety of our throwaway mode. Don’t try to clean brushes
customers in mind. However, it is not with solvent - toss them out. Tools like putty
possible to make a hazard-free epoxy resin knives can be wiped with a paper towel then
system. As with all chemical products, they sanded clean after the epoxy cures. Cured
must be handled properly to minimize epoxy doesn’t stick to polyethylene or wax
health risks. Material Safety Data Sheets paper. Gloves, disposable brushes, and one
(MSDS) are available upon request for time use roller covers are expendable. Your
all of our products. health is not. Think of gloves and dust masks
as another part of the cost of the project,
The primary hazard when working with an being prepared to spend some money on
epoxy system is skin irritation leading to these items designed to help protect you.
possible skin sensitization from prolonged We like the inexpensive disposable gloves
and repeated direct skin contact. Most as opposed to heavier, more permanent
people who become sensitized are unable gloves. The problem with the heavier gloves
to continue working with epoxies without is that they eventually become contaminated
breaking out in a rash commonly on the with uncured resin or hardener on the inside
inside of the forearms and on the forehead long before they wear out. The very thing
above the eyebrows. The effect appears to be that you started using to protect you is now a
cumulative. That is, you might be able to get source of contamination. Disposable gloves
away with getting epoxy on your skin for wear out about the time they become dirty
awhile but sooner or later it can catch up to and are replaced.
you and you will be sensitized. We would
like to emphasize that these products can
be used safely for a lifetime – if handled
properly.

5

The vapor pressure of epoxy resins and Develop a measuring technique that is
hardeners is so low that vapors rarely cause sufficiently accurate and then stay with it.
problems, unless you have already become Doing it the same way each time will minimize
sensitized. Well-cured resin should cause no the chance for error. In the interest of simpli-
problem, as it is largely inert. fication the following discussion assumes a
2:1 volume ratio. Refer to our catalog for
Whenever sanding or creating any kind of specific product mix ratios.
dust wear a mask along with safety glasses
and gloves to keep the dust out of your If you are using some type of graduated cup
lungs. If you sand fiberglass and allow the or a straight-sided can, get in the habit of
dust to get on your skin you will probably get measuring the same way each time. If you
an itch from the glass fibers. Shower in cool pour the resin first, then always pour the
water to wash the fibers off you. The itch resin first. Before you add the hardener,
usually goes away after 24 hours. notice how much resin is already in the
container, divide this by two (for a 2:1
Epoxy resins and hardeners have a low system) and then add hardener to bring
flammability risk generally burning only if the total to the correct mark. Measuring in
exposed to a high heat source. BUT, the the same order each time will avoid the
solvents found in S-1 and Titanium are common error of two parts of hardener to
flammable, and vapors can even be explosive one part of resin.
in the right concentration. Be smart and
avoid any possible source of ignition when Using a vertically held stir stick marked in a
using solvents. two to one ratio will only work for vertical
sided containers. Don’t use this method on
Most people never develop health problems containers with sloping sides.
working with epoxy resins. If we scared you
a little then it’s our hope that you’ll work with If you use the “two measures/one measure”
these materials a little smarter and cleaner method and mix in a separate pot, be sure
than you might have otherwise. to scrape the sides each time you pour from
your measuring cups to the mixing pot.

Measuring and Mixing Make sure the graduations on disposable
cups look right. Some paper cups are not
Epoxy Systems rolled correctly when made – the first
graduation sometimes is too high or too low.
Measuring and mixing is really easy because We can’t inspect each cup to make sure it
most of our epoxy systems mix at a 1:1 or was properly made – this is your job.
2:1 volume ratio. This doesn’t mean you
don’t have to pay attention to what you’re For small batches less than 90 ml (3 oz.)
doing. Occasionally a customer will call use the syringes or accumeasure kit.
suggesting that something is wrong with
the epoxy because it didn’t cure properly. Industrial Formulators Inc. offers one
We know of no situation where the resin/ mechanical pump for those who desire
hardener has gone bad or has been the convenience that is devices provides.
contaminated and wouldn’t cure. It always These pumps are the kind that you find at
resolves that the batch was either improperly the ballpark and use to get mustard out of
measured or insufficiently mixed in the the jar to put on your hot dog. Complete
user’s shop. Epoxy chemistry just will not instructions come with each plunger pump
allow it to work any other way. kit. We recommend using the pumps to
dispense, not measure. Pump into a graduated
Measuring errors are insidious and can pop mixing cup or tub to be double sure of an
up when you least expect them. These errors accurate measure.
usually occur because you changed your
technique, were in a hurry, had someone
else mix a batch, or were just not careful.

6

Be aware that any mechanical device can
go haywire, lying to you with a straight face. Techniques of Epoxy Use
Valves can stick causing backflow into the
reservoirs. Cool temperatures can cause the Four epoxy application techniques are
viscosity to change. The rate or speed that commonly used. These are coating,
you pump can alter delivery volumes. fiberglassing, gluing and filleting/fairing.
Furthermore, the techniques are pretty much
Epoxy systems can be measured by weight the same whether they are involved in wood
as well as volume. The correct ratios vary so or fiberglass construction and repair. After
if you plan to mix by weight give our technical all, coating with epoxy involves the same
support line a call. Don’t make the mistake of technique and tools regardless of whether
using the volume ratio when measuring by the substrate is wood, fiberglass, or some-
weight. The hardener is less dense than the thing else.
resin you’ll use too much hardener and get
an incomplete cure. What might seem to be other techniques are
usually just variations or combinations of the
Large batches (a litre or more) are most above. Many of our epoxy users discover
efficiently measured by weight. A postal new variations. We will discuss a number
scale is usually accurate enough for the of these variations and the “tricks” that will
larger batches. An O’Haus triple beam make the epoxy work go easier and faster.
balance will allow for the accurate weighing We don’t know everything and are constantly
of batches from as little as a few grams to learning something new. We invite you to
over 2.5 kilograms. learn along with us.

With the resin and hardener accurately If you come up with a variation that we don’t
measured, mix thoroughly. Stir well, scraping mention, model it first to see if it will work.
the container sides, and mix from the bottom Do this prior to using the whole project as a
to the top. Keep stirring until that mixture is test. For example, we are often asked if Cold
no longer hazy. Don’t worry about a few air Cure epoxy will stick to stained wood. Most
bubbles. That’s normal. Scrape the mixing of the time it will if stain used is water or
stick several times on the side of the container alcohol based. However, the only way to be
really sure is to conduct your own little test.
Don’t make large batches. Keep in mind that
large batches take longer to mix, have a Suppose that you are staining a piece of fir
much shorter pot life, and if you get side that will later be coated with epoxy and have
tracked cost more when they gel in the pot. another piece laminated to it. First, stain a
Epoxy paperweights are expensive. scrap piece of the same wood; allow it to dry
well (several days). Laminate on two pieces
If you measured or mixed incorrectly and of 3 or 4 inch wide fiberglass tape about
a batch doesn’t properly cure about the fifteen cm long. Leave a “tail” that can be
only thing to do is scrape it off and start over. grasped later with a pair of pliers by running
A hot air gun will help to soften the partially the tape about half way up on a plastic
cured material. Then try removing any squeegee. Let the epoxy cure a day or two.
residual with acetone, MEK, or lacquer Remove the squeegee and grab the tail with
thinner (but not with the hot air gun or the pliers. Try to peel the tape off the substrate.
source of ignition around). Wear solvent If the tape tears where the tail starts leaving
resistant gloves and have plenty of ventila- the balance of the tape bonded to the surface,
tion when doing this. Then examine your then the bond is good. If the whole thing
technique to find out what went wrong. pops off intact then the bond is bad and the
stain is interfering with the bond strength.
Better find a new stain and repeat the test.

This same procedure can be modified to test
the ability of the epoxy to bond exotic woods.
If the failure occurs in the wood when two

7

pieces are glued rather than in the glue line pull away from the surface creating craters.
then it is safe to assume that the epoxy Overheating will also cause the expansion of
works on that kind of wood. any air in the pores of the wood and may
result in an epoxy coating full of bubbles.
In order to simplify the following discussion
of the four main areas of use for our epoxy Sometimes a coating will try to crater. This
systems we are going to confine the discus- is most common with coatings that are too
sion to using Cold Cure epoxy with plywood, thin, recoated surfaces that have not been
a common building material. Where appro- thoroughly sanded or on contaminated
priate we will mention the use of our other surfaces but may happen on other surfaces
epoxy systems. The sections following this as well. While the cause of cratering is quite
will discuss modifications of the four tech- complex, the solution is pretty simple.
niques for specific areas of building and Immediately after coating a surface look at
repairing fiberglass structures. We feel that if it from an angle, sweeping your eyes over
you can understand and use the following the whole surface. Craters will usually form
techniques then you will be able to skillfully within ten minutes after first applying the
do most kinds of epoxy work. coating. If cratering occurs, take the heel of
the foam roller and really grind it in the area
that has cratered. This wets out the dry spots
Coating with Epoxy Resin in the crater center. Then, re-roll the area
treated to even out the coating.
Whenever possible it is best to do coating
operations on the bench. If the part is too Cold Cure epoxy will bond and cure in thin
large or cumbersome to place on the bench, coatings in cold, damp conditions without
then whenever possible arrange your work any special tricks, but giving it an induction
so that it is horizontal. When working flat period will help speed things along. After
you’re not fighting gravity and the coated mixing the resin and hardener allow the mix
panel is easily sanded on the bench using a to sit in the pot for 15 to 20 minutes. Then
disc sander and foam pad. Coating a sheet apply it in the usual manner. The use of a hot
of fir plywood will illustrate this method. air gun will help level a cold epoxy coating
but it is not necessary to aid in the cure.
Mix the resin and hardener in the correct
ratio. Pour this mix on the plywood in a After 24 to 48 hours (depending upon
stream of “S” curves starting at one end and temperature and hardener used) the coating
finishing at the other, making four or five will be cured enough to sand. First wipe the
curves along the length. Spread the epoxy surface with a damp sponge to remove any
back and forth with a squeegee into the dry water soluble amine carbamate surface film
areas, trying to get as even a coating as prior to sanding (for Jet Cure or 51-Cure
possible without being too fussy. Use a dry only). At this stage of cure the epoxy coating
foam roller to even out the coating. When can usually be sanded with a disc sander
this first coat is cured to at least a soft set and a big foam pad starting with 60 grit
tack free stage it can be recoated. paper. Disk sanding can generate quite a bit
of heat, especially when the sandpaper gets
Use at least two coats for interior wood and dull or clogged, causing gumming of the
three in areas that may be constantly wet. sanding disk. Keep the sander moving and
apply only light pressure. This keeps the
Several tricks can be used to improve the heat down. If clogging still happens you’ll
appearance of the finished film. Bubbles that have to either hand sand, scrape as described
persist in the coating can be broken with a below, wet sand or allow another day for the
foam brush by lightly dragging it across the cure to proceed.
surface. Fanning the uncured surface with a
hot air gun or hair dryer will accomplish this Scraping is an alternative to sanding that
with greater speed. Avoid overheating an actually produces a better finish. This shaves
area as this could cause the epoxy film to off a thin film of epoxy leaving a surface that
looks like it was sanded with 600 grit paper.

8

Small parts can be scraped using a single more coats of varnish and is much more
edged razor held vertically. Several companies durable. Revarnishing is much easier
make wood scrapers for working on larger because the old varnish is just removed
surfaces. Keep them sharp and be careful down to the epoxy coating.
not to cut yourself.
Epoxy coatings should be sanded before
Sanding dust should be removed by blowing varnishing or painting. These materials stick
or brushing it off prior to recoating. The final to the epoxy by mechanical means and must
bit may be removed with a damp rag. Don’t have some “tooth” in order to bond well.
use acetone, or other solvents. Tack rags may
leave an unbondable surface coating on the
sanded epoxy surface.
Fiberglassing with
Some amine cured epoxy surfaces are Epoxy Resin
quite alkaline and can react with any acidic
material such as moist carbon dioxide or Exterior surfaces usually use fiberglass or
silicates. Further epoxy coats may not bond other woven cloth material as a reinforcement,
well to some of these reaction products. or substrate, allowing a thicker, stronger
Sanding, in addition to providing some epoxy coating which results in higher
“tooth” for mechanical bonding, also cleans abrasion, impact and moisture resistance.
since it exposes new, uncontaminated In the case of most wood composite structures,
surface. If in doubt, sand. the purpose of this reinforcing cloth is to
strengthen the epoxy coating, not to reinforce
Try to work at a constant or falling temperature the part.
when coating. When the temperature is
rising, air trapped beneath the uncured Cold Cure epoxy is a much better choice
epoxy may expand and cause small bubbles over wood than polyester resin. Polyester
to form in the coating. Avoid working in is a poor adhesive because it shrinks and
direct sunlight for this reason. If you must delaminates then it lets moisture get between
work in sunlight, do your coating as the sun the fiberglass and the wood substrates.
is going down. The surface will be cooling
and air bubbles should not form. Evening Because the fiberglass is structural to the
dew condensation does not harm the epoxy coating rather than the part, it’s
partially cured Cold Cure epoxy coating. possible to use a lightweight cloth. Don’t use
a cloth a that is too heavy for the intended
Some very porous materials are quite service, you’ll use a lot more epoxy and have
persistent at forming air bubbles. A trick we a heavier part, gaining little else. Tests run
have used is to heat the whole surface to a with Cold Cure epoxy show no appreciable
temperature about 60°C (140°F). Use a hot difference in peel strength between the two
air gun or place the wood in the sunlight for most popular finishes of fiberglass cloth,
awhile. Stop heating and immediately coat Volan and Silane. Four and six ounce cloth
the surface. The epoxy will thin on the warm are nearly invisible when wet out with clear
surface and at the same time start to cool it. epoxy resin. Heavier weight cloths begin to
The air in small pores will begin to contract show the weave pattern under certain
pulling the thinned epoxy into them. Any air lighting conditions.
that does rise will be going through thinned
epoxy and have an easier time of it. Avoid using fiberglass mat with epoxy resins.
The binder that holds the mat together is
Cold Cure is an excellent base for varnish. designed to be dissolved by the styrene in
The application of multiple coats of varnish polyester resins. Most epoxies don’t use
and sanding between coats can be eliminated styrene as a diluent, making it almost impos-
with NO sanding between coats. The final sible to wet out the mat. Woven roving is wet
epoxy coat is sanded to provide a base, then out well by epoxy although we know of no
one or two coats of varnish are applied. The reason to use it when building a wooden boat.
result appears to have the depth of ten or

9

Regardless of the type of the cloth or resin When this first area has been covered and
system used, fiberglassing is done essen- the cloth has disappeared, take the squeegee
tially the same way. There is no need to be and use a fair amount of pressure to squeeze
intimidated by fiberglassing, what you are the excess resin away from the wet cloth,
really doing is gluing the cloth to the surface working it down into the dry cloth area.
with a minimum amount of resin. Use just This removes excess resin and trapped air,
enough epoxy to wet out the cloth, you’ll fill sticking the cloth down right next to the
the weave of the cloth later with more epoxy. wood surface. The squeegeed cloth should
now have a semi-dry look with the weave
Work on as horizontal a surface as possible. pattern showing; the cloth itself will be
Fiberglassing is much easier if you are not invisible.
fighting gravity.
Keep on going, section by section, until you
The first step in doing a good fiberglass job are finished. If you are working on a very
is to precoat the part. This avoids the problem large area use a dry roller cover on the
of having an unsealed porous structure soak previous three or four sections to give a
up too much epoxy, starving the bond. final smoothing. On smaller boats the roller
Precoating doesn’t use any more epoxy can be used after the entire hull has been
than the more difficult one step method fiberglassed.
(for experienced fiberglasser’s only!) and
helps to assure that maximum peel strength Let the epoxy resin cure to the “green state”
is achieved. After the first coat cures fill any stage where it is pliable but no longer tacky
holes with an epoxy/microballoon mixture unless pressed really hard. Now’s the time
to provide a smooth base for the cloth. to trim the excess cloth. Trim by running a
Sand lightly but thoroughly to a uniform dull single edged razor blade around where the
surface. Clean the surface with clean, oil free glass overhangs the edge. Press down any
compressed air or brush off and wipe with a glass that may be lifted from the surface
clean damp rag to remove any remaining while trimming.
traces of dust. We do not recommend using
acetone or similar solvents for this. Much The selvege edges of the fiberglass have to
acetone sold today is reclaimed and may be feathered before being covered by another
have impurities that interfere with secondary piece of cloth. Wait another hour or so and
bonding by leaving a film of residue on the do the feathering with a Surform. Do it while
surface. it is in the right state of cure. Too early and
the wet fiberglass will lift, too late and it will
Next lay the fiberglass out on the precoated, be too hard to cut. The alternative is to wait
tack free surface, smoothing it out and doing a day or so until it is hard enough to sand.
any rough trimming. Masking tape may be
necessary to hold the cloth in place if the It is not always possible to have a selvage
surface has any slope. edge on the cloth. Rather than have a cut
edge fraying all over the place which can
Mix no more than 300 ml of resin and 150 only be cleaned up by a lot of sanding later,
ml of hardener. Work with small batches here’s a trick that produces a very neat edge.
until you get the hang of it. Start at one end Run a piece of 2” masking tape so that the
and pour the resin out over an area equal to inner edge of the tape is where you want to
about 50 ml per square ft. (450 ml does a stop the glass. Lay down the cloth so that it
1 square meter area). Pour in “S” curves as runs at least an inch past the outer edge of
described in the coating section (on steep the tape. Wet out the glass past the inner
surfaces apply the epoxy with a roller cover edge and about half way across the tape.
and roller tray), spreading lightly into the dry When the cure reaches the green state run a
areas with a squeegee. We like the rubber single edge razor blade right down the inner
squeegee for laying down cloth. Let the resin edge of the tape. Pull off the tape and presto,
wet the cloth out. Don’t try to “force” it through you have a nice edge right where you cut
the weave with the squeegee. Notice how the fiberglass. If a little of the cloth lifts, press
the cloth disappears as it wets out. it back down.

10

The weave of the cloth can be filled once the roller cover and a roller pan. Use just
resin has reached the green state of cure, enough epoxy to wet out the cloth. When
preferable the same day. If this is not practical, cured finish in the usual way.
sand lightly but thoroughly before recoating.
Don’t try to sand the weave smooth, fill it Corners and edges often require several
with epoxy. Apply fill coats the same as layers of cloth. Giving thought to a “glassing
discussed in the preceding section on pattern’ will allow doubling at chines and
coating. Several coats may be necessary sheers without going through extra steps.
before the weave is filled. It is possible to Corners are most easily “patched”. Cut
thicken the epoxy slightly and do it in one circles of different diameters from cloth
coat using a squeegee. Anti-sag Powder scraps. Wet down, dabbing at it with an
(Cab-O-Sil) works best but don’t use any epoxy soaked brush. Lay down the next
filler on surfaces that are to be clear finished. larger circle over this wetting it with more
epoxy, if necessary. Continue the process
When the weave has been filled the surface until finished. Each larger circle will fray the
should be sanded to prepare it for painting cut edges of the smaller circle under it. This
or varnishing. Sand the epoxy, not the process is called self-feathering. Use the
fiberglass. Be sure to wear a respirator or masking tape trick for the last circle and the
dust mask, gloves and a disposable paper job will require little sanding to look nice.
suit while sanding. If you do get the fiber-
glass itch take a cool shower, it will go away Heavy structural seams are best-done using
in a few hours. biaxial tape. Biaxial means that the fibers
run at 45 degrees to the way the tape comes
Applying fiberglass overhead is at best a off the rolls. When run along a seam ALL
difficult, messy job. Anyone who has tried it the fibers run across the seam at 45 degrees.
once has no desire to repeat the experience With regular plain woven tape half the fibers
and will do everything possible to try to turn run parallel to the seam and add nothing
the boat over or at least work on a slant. If to strength.
this is not possible then there are several
suggestions for accomplishing this job. Biaxial tape is heavy at 18 or 24 ounces per
square yard and it won’t be clear like lighter
If you are working on a relatively small area, tape when wet out with epoxy so don’t use
wet the surface with mixed resin/hardener it for bright finished seams. Rather than
and lay a rough cut piece of cloth into the featheredge biaxial tape by sanding we
resin. Surface tension will hold it into place prefer to fair the edges using an epoxy/
without sagging if too much resin is not balloon mixture.
used. Using a squeegee overhead is a feat
no one has yet mastered. Use foam rollers. In summary, fiberglassing is a three-step
Once the epoxy has cured you finish the process:
overhead area in the usual manner.
1. Seal the porous surfaces to prevent
Glassing large overhead areas calls for a starving the joint. Do filling and fairing
different technique and a helper or two. on the sealed surfaces. Sand lightly but
Most successful jobs are done by rolling on thoroughly.
a coating, then allowing it to cure to a tacky
state. The cloth is then rolled as smoothly 2. Stick the cloth down leaving a minimum
as possible onto the tacky coating. This is amount of resin in the cloth.
where you’ll probably need more than one 3. Fill the weave any time after the wet
person. Get the wrinkles out as you go along; cloth has reached the “green stage” and
you won’t be able to slide them out because is stuck to the substrate.
the tackiness of the coating will hold the
cloth in place. Once you’ve got the cloth
where you want it press it into the tacky
undercoat with a dry foam roller. When it
is all smoothed down, wet it out using the

11

filleting putties to improve tensile strength,
Using Fillers with and are listed above in descending order of
Epoxy Resins tensile strength improvement.

Cold Cure epoxy properly mixed is intended Paste pigments (titanium dioxide), black
for both coating and fiberglassing. When paste (Carbon Black) and aluminum powder
used “right out of the jug” the mixture is said are generally used as pigments. Adding
to be “unfilled” and it is too thin to be used white paste pigment produces a white resin
as a gap-filling adhesive or for fairing and coating that is useful for areas where a light
filleting compounds. For these applications color is desired and painting is difficult.
certain fillers are added. These materials Pigments aren’t meant to serve as substitutes
change the flow and density characteristics for paint in areas exposed to direct sunlight.
of the epoxy system. White paste pigment is useful when added
to the final fill coat when fiberglassing,
All powders sold for use with Cold Cure allowing this coat to serve as a cover coat
epoxy products are solid materials, falling for finish painting.
into four general classes: thixotropic agents,
bulking agents, fibers, and pigments. There Our pigments are pure dry colorants ground
is some overlapping as to function of certain into epoxy resin to produce an epoxy paste
fillers. For example, plastic minifibers is both pigment. Since they are dispersed into
fibrous and acts also as a thixotropic agent. epoxy resin they may be added to the resin
side of our epoxy systems to produce a
Anti-sag powder (Zeothix), plastic minifibers stable pigmented resin. Measure the amount
and wood flour are thixotropic agents. They of the pigmented resin used to determine the
turn the epoxy into a thixotropic fluid. Most amount of hardener required. Used in very
people are not familiar with the term “thixo- small amounts these pigments are transparent
tropic” though everyone is familiar with the in an epoxy and can be said to act as dyes.
properties of these fluids. They flow under In larger amounts they are opaque.
shear stress but do not flow once the stress
is removed. Adding these agents to the Fillers change the mechanical properties of
mixed resin and hardener produces a fluid, the cured resin, however, for all practical
which will easily flow under the spreading purposes these changes can be ignored.
stress of a putty knife. Once the stress is Thixotropic agents have the least effect since
removed the thickened epoxy retains shape. they are used in the smallest amounts to
In short, these powders make the epoxy produce the desired result. Bulking agents
non-sagging, being added to restrict drainage reduce tensile strength in proportion to the
and make gap filling adhesives. amount added. Some will initially increase
compressive strength. With increasing
Phenolic microballoons, quartz microspheres, amounts of additives, though, compressive
and wood flour are bulking agents. They strength will decrease.
“bulk out” the epoxy making a lightweight
putty-like mix. Although all these thicken Numerous combinations of filler materials
the epoxy, only wood flour will make it are possible and we have not tested them all.
thixotropic. Attempting to add sufficient If you have an idea that a certain combination
microballoon or microspheres a non-sagging might do something special for you then
fairing putty will result in one that spreads check it out. Little pieces of scrap plywood
poorly. These materials should be used are good for this. Think up some destructive
along with a thixotropic agent. Anti-sag tests that will simulate the stresses the
Powder is the best choice because it produces material will see in service. Check to see
the smoothest compound. where the failure occurs. If the wood breaks
then your combination should work well
Chopped glass strands, milled glass fibers, with wood, at least.
and plastic minifibers are fibrous materials
that can be incorporated into structural

12

This is the correct sequence for the addition wood scarf joints are made at a minimum
of filler materials: 8:1 slope. Fillets increase glue surface area
and are used to relieve stress concentrations
1. Correctly measure and mix resin/ that build at right angle corners. Stringers,
hardener for example, should have fillets where they
2. Add fiber fillers, if any and mix well butt onto planking.
3. Add bulking agents, if any and mix well
4. Add thixotropic agent and mix well. Second, make sure that the surfaces being
glued are clean, free of grease, oil, wax, and
other contaminants that could act as release
Epoxy Resins as agents. If the surface is coated with cured
epoxy, sand before gluing and wipe the dust
Structural Adhesives off. Remove paint rather than trying to glue
onto a painted surface. Epoxy resins stick
The mixed viscosity of Cold Cure epoxy is well to paint although the overall bond
not high enough to make a good gap filling strength will be no better than the paint to
adhesive. Thixotropic agents like Zeothix, substrate bond.
Plastic Minifibers, and Wood Flour are used
to thicken the epoxy and change the flow Third, do not overclamp. Epoxy resins
characteristics. These fillers will turn the require only contact pressure. Overclamping
epoxy from translucent to opaque depend- can squeeze most of the adhesive out of the
ing on the type and amount used. Anti-sag glue joint and the epoxy that is left may be
and Plastic Minifibers make the powder absorbed if the surface is porous, starving
epoxy whitish while Wood Flour turns it the joint. A glue-starved joint is very weak.
reddish-brown. Anti-sag makes a smooth Use only enough pressure to hold the joint
material while epoxy thickened with Plastic immobile and keep the two surfaces in
Minifibers or Wood Flour will be coarse. contact until the epoxy has set – overnight
at normal temperatures. Nails, screws,
Microballoons and microspheres should not clamps, rubber bands, or staples can all be
be routinely used in an adhesive formulation utilized to do this holding job. Clamp just
as they reduce tensile strength. Quartz hard enough to close up the joint.
Microspheres may be used as a filler/
thickener for cold molding where the surface Fourth, remember that epoxy resins continue
area to be bonded is large with respect to the to cure and build strength for several days
mass. Microspheres are acceptable here after they solidify. Joints that will be under
because of the large glue surface area immediate stress once they are unclamped
involved and the low microsphere loading need more cure time before the clamps are
level. removed. Overnight cures are usually
sufficient for most non-stressed joints. A
Making an epoxy glue joint is quite simple. common cause of epoxy joint failures is too
First, properly measure and mix the resin much stress before the epoxy has reached
and hardener, then coat both mating surfaces sufficient strength. Such a case might occur
with this unfilled epoxy to wet them out. It is where a scarfed joint is unclamped and bent
not necessary to let this coat cure. Next add into place too soon.
the thixotropic agent to the balance of the
mixed resin/hardener blend and spread this Fifth, protect any finished wood glue joint
thickened resin on either of the two surfaces from weather degradation. Wood that is
to be glued and close up the joint. That’s all allowed to weather will cycle through moisture
there is to it – but there are some tricks and content extremes. Wood expands as the
things to keep in mind. moisture content increases. This expansion
can set up enormous stress concentrations
First, remember that the ultimate strength of across the glue joint due to uneven rates of
any glue joint is a function of the glue expansion on either side of the glue line.
surface area. The more surface area, the These stress concentrations can exceed the
stronger the joint. This is the reason that strength of any glue, including epoxy resins,

13

causing failure. Protecting the joint by epoxy Epoxy resins usually bond well with cured
coating all surfaces of the glued wood stops thermoset materials like polyester, vinyl
the moisture cycling and prevents failure ester, and other epoxy resins as long as the
because of weathering. This is not a problem cured surface is sanded and wax free. However,
for wood glued with epoxy that will not be you should not try to bond polyester, vinyl
subject to deep moisture cycling. ester, or other polymeric materials which are
cured with MEKP or other peroxide catalysts
Cold Cure epoxy works well for use as an to cured epoxy resins.
adhesive for wood-to-wood and fiberglass
cloth-to-wood bonds. When we are asked if There are too many materials and combina-
it can be used to bond metals and plastics tions to cover every possibility. We suggest
the general answer is that it depends on the that you model any questionable materials
materials involved and their intended use. that you want to bond. Glue some scraps
and test them. Try accelerated aging and
Metal/metal bonding success depends retest them. If they survive an hour in 70°C
upon the type of metals bonded, the surface (160°F) water they will probably last for quite
preparation, and the intended service a while. You have the ultimate responsibility
temperature. Generally, we recommend for your own work.
against making structural metal/metal bonds
with epoxy resins unless they are specifically Sometimes there’s a need for clear gap
formulated for that purpose. Our testing filling thickened epoxy. It’s not possible to
shows that these bonds degrade over time produce such a material using any of the
due to different thermal expansion rates solid thixotropic agents previously discussed.
setting up shear stress and resultant interfacial Our G-1 glue is handy for this since it is
failure. For non-structural applications the clear and thick.
flexible mastic materials appear to hold
better than the more rigid epoxies as they 5-Cure is our 1:1 “five minute” epoxy. Items
allow for thermal expansion. glued with 5-Cure can be stressed in as little
as 10 minutes. It is very handy to have in the
Metal/wood bonding for non-structural shop for this reason. Builders often find that
applications may be done successfully with “missed screw hole” when ready to lay down
Cold Cure epoxy providing that the metal is the fiberglass cloth. Mix a little 5-Cure, add
clean and bright. Structural applications are some Wood Flour or Anti-sag and you’ve got
best when they are mechanically fastened. an instant putty to fill the hole. 5-Cure can
Don’t put stainless bolts in epoxy resin. also be used in combination with Cold Cure
Stainless steel works only in the presence as a “spot welder” where clamping is all but
of sufficient oxygen. The epoxy will deprive impossible.
it of oxygen causing crevice corrosion in
the presence of an electrolyte like seawater. Coat the pieces to be bonded with thickened
Stainless steel fastener failure occurs where Cold Cure epoxy except leave several golf
the bolt emerges from the epoxy resin. ball-sized bare areas. Mix some 5-Cure and
apply to the bare areas. Push the pieces to
Bonding to metal alone such as fairings on be bonded together with enough pressure
lead keels will work well with Cold Cure to cause some “ooze out”. Hold in place for
epoxy so long as the lead is bright and free about five minutes until the 5-Cure hardens.
of oxidation. Now the 5-Cure will hold the pieces together
while the Cold Cure epoxy sets.
Thermoplastic materials like vinyl, PVC
or ABS generally bond poorly with epoxy Unlike our other epoxy systems 5-Cure and
resins. If you need to bond any of these test 30-Cure, like all similar epoxy products, is
them yourself. You will get the best results if water resistant, not waterproof. It is fine for
you first sand the plastic with coarse paper. intermittent water contact but should not
Epoxy will not bond to polyethylene, be constantly immersed.
polypropylene, or Teflon. It bonds well
to neoprene and polyurethane rubbers.

14

than sanding the whole fillet down to a
Filleting, Fairing, and common level. Blow or brush off the sanding
Molding with Epoxy Resins dust (wear a dust mask!). Make up some
more filleting compound and use a broad
Cold Cure epoxy is mixed with phenolic putty knife to fill the low spots resting the
microballoons (purple), quartz microspheres blade against the fillet parallel to the long
(white), or wood flour (brown) to make putty- axis of the filet. Allow the putty to cure and
like material that is used for making cosmetic do a final sanding. That’s it! Perfect fillets in
or structural filleting, fairing, or molding two easy steps with little sanding.
compounds. Rather than supply these
compounds in a premixed form, we supply Before microballoons are painted they
the raw materials so that builders are should be sealed with epoxy or else the
allowed the versatility of creating customized paint goes into the tiny hollows in the
compounds to fit a specific need. broken balloons and the finish will appear
ragged. Brush or roll on a coat of epoxy on
Filleting is the process of adding an epoxy the sanded balloons, allow to cure and sand
putty to concave angled corners for cosmetic lightly before painting.
and structural reasons. Cosmetic fillets are
generally “low density” being made by the Structural fillets increase the glue joint
addition of microballoons which “bulk out” surface area relieving stress concentration
the epoxy. Structural fillets are “high density” zones that occur at angled corners. They are
and are thickened with anti-sag mini-fibers usually made at the same time that the piece
or wood flour. These fillets sometimes creating the corner is attached. For example,
contain glass fiber. Thixotropic agents make when sheet plywood is glued onto a stringer
the mix non-sagging when sufficient the excess glue that oozes out can be used
amounts are used. Microballoons and to form a fillet. A gloved finger makes a
microspheres do thicken the epoxy, but good filleting tool, as these fillets don’t
when used in proper loadings do not need to be large.
prevent sagging, and need the addition of
a thixotropic agent. Large structural fillets are generally made in
a separate operation in a manner similar to
Cosmetic fillets are applied by putting an making cosmetic fillets. If they aren’t going
excess of material along the length of the to show there really is no need to make them
corner with a putty knife or caulking tube. pretty. The addition of either milled glass
Be careful not to force big air bubbles into fibers or chopped glass strands improves the
the fillet when putting the putty in the tensile strength of structural fillets.
corner. A rounded tool is used to shape the
putty by drawing it along the fillet. The sides Fillets in stitch-and-glue construction usually
of the tool should touch both sides of the are fiberglassed. The easiest way to do this is
corner and the tool radius is determined to fiberglass the fillet when it is in a semi-stiff
by how rounded the finished fillet will be. state so that it can still be pushed around with
Almost any material can be used to make an epoxy-saturated brush. This saves having
a fillet tool. Plywood paddles work well, to sand the fillet after it is cured.
are easy to make and are inexpensive.
The excess putty will be forced out on Fairing is the operation of filling the low
either side of the tool where it is scraped spots to the level of the high spots, eliminating
off with a putty knife. waviness and hollows. The compound used
is identical to that of the cosmetic fillet and
Once the fillet is cured it may be sanded. the operation is similar except that large flat
A round edged sanding block with coarse areas are involved. Large drywall broad
(50 to 60 grit) paper works best. Knock off knives, stiff boards with tapered edged
the high spots with the sandpaper and then squeegees, and similar tools are useful for
come back and fill in the low spots with an fairing. Once the putty has cured it is sanded
additional batch of putty. This is much easier with large blocks to a level fair with the
surrounding area. On very large areas low

15

spots may appear during sanding that will months of intense tropical sunlight on
need a second fairing. After final sanding the horizontal surfaces. Total breakdown will
fairing compound should be sealed with occur about 15 months under these same
epoxy prior to painting. conditions.

A slick way to fair a large area and avoid a Bright finished boats should be finished with
lot of tedious sanding is to use a serrated a clear coating that contains a UV inhibitor.
trowel like the metal one floor tilers use to This inhibitor is sacrificial so the coating
spread mastic. Apply the fairing putty using must be periodically renewed if the epoxy
this tool leaving a series of parallel ridges is to be protected. When the clear coating
that stand proud of the surface. Allow the starts to look dull it’s time to refinish. Old
putty to cure, then sand the area. Notice that coatings are removed by sanding or are
all you are sanding is the tops of the ridges – chemically stripped with strong solvents.
about one fourth of the total surface is being Test patch an inconspicuous area to make
faired. Sanding dust falls into the valleys. sure that the solvent used does not attack
Once the ridge tops are fair, the area is the epoxy base. Solvents and removers
cleaned of sanding dust and the valleys are containing methylene chloride will etch
filled with fairing compound using a broad epoxy surfaces. Don’t use these. Be sure
knife with a straight edge. Only a light to observe the usual precautions when
sanding is then required for final fairing working with these solvents.
following cure. Seal with epoxy before
painting. Opaque paints do not allow the passage of
UV light, offering the best protection of the
epoxy coating. A primer coat prior to painting
Painting and Finishing over Industrial Formulators epoxy with these
paints is quite helpful for several reasons.
Over the years nearly half of the technical
service questions we’re asked involve Besides bottom paint, three broad classes of
painting and varnishing. More than anything coatings are commonly used as boat paints.
else this has been the area that has caused These are the “one part” alkyd and modified
most people trouble. We have solved these alkyd enamels commonly called “oil base
problems by developing our own painting paints”, the “two part” epoxy and the two part
system for epoxy resin surfaces – more on linear polyurethane (LPU) paints. Since all
this later. epoxy based materials eventually chalk in
sunlight be careful to consider exposure
Industrial Formulators epoxy surfaces may when using the two-part epoxy paints for
be coated either with opaque paints or exterior finish coats. Two part epoxy primers
finished with clear varnishes. The epoxy are recommended as high build sanding
surface accepts finishes like any other non- base primers for LPU paints.
porous surface except that it is chemically
active to certain materials because of Be sure that you are getting what you expect
unreacted amines on the surface and when purchasing a marine paint. Paints sold
throughout the epoxy matrix. in marine stores today are a triumph of
marketing over technology. Remember the
All outside epoxy surfaces exposed to adage: “The big print giveth while the small
sunlight must be protected from degradation print taketh away.” It is not uncommon to see
by ultraviolet (UV) light. This is the invisible the pretty face of a paint can staring back at
short wave length portion of sunlight that you screaming “Buy me! I am a one part
causes sunburn. The long-term effect of UV polyurethane”. Yet, when you read the back of
on unprotected epoxy is a dulling of the the can you find that the ingredients state that
clear film, followed by chalking and, finally, it contains polyurethane safflower alkyd resin
film cracking and delamination. The initial or some other modified alkyd. If it says alkyd
effects of UV degradation on Industrial anywhere on the can then it is an alkyd NOT
Formulators epoxy start after about six a polyurethane. True polyurethanes often

16

referred to as LPU paints are two parts and “Test patches” are advisable prior to paint-
cost about two to three times what an alkyd ing or varnishing over an epoxy coating.
costs. If the ingredients are not specified on These test patches will give you a feel for
the can, then ask for a MSDS on the paint. how the various coating materials handle
and point out any possible incompatibility
Alkyd enamels and related one part solvent- problems to their becoming a disaster all
based paints and varnishes are easy to work over your boat.
with but may not properly dry on epoxy
resins. They may be brushed, rolled or To do a test patch, coat a small area with the
sprayed and dry to a glossy film that is easy painting system selected to make sure that
to refinish. Their main drawback as a finish each paint layer dries properly and adheres
is that they are softer than LPU paints and well to its substrate. One reason for doing
chalk slowly over a period of time. this is that epoxy resins, despite sanding and
long cure time remain chemically active to
LPU paints dry very hard with excellent certain components of alkyd paint and
gloss, are not degraded by sunlight and varnish systems. Generally, epoxy primers
wear very well. Their main drawback is that and LPU paints are compatible with epoxy
they require immaculate surface preparation. resin coatings and may even chemically
The solvent based LPU paints contain some bond. However, some of the alkyd enamels
very hazardous materials and are difficult to and other one part paints and varnishes may
apply. They can turn dull when curing if the not properly dry on epoxy resin coatings.
humidity is too high. Our experience is that The free unreacted amine in the epoxy resin
the application of solvent based LPU paints coating interferes with the action of the
is beyond the skill of most amateur mettallic driers in some of these paints.
boatbuilders. If this happens the paint may surface dry
but remain soft and tacky next to the epoxy
Because of the ultra high gloss and thin resin surface.
film of LPU paints any imperfection in the
substrate will show in the finished coating. A similar chemical phenomenon occurs
Thus, the tendency of the alkyd paints to between the amines in epoxy hardeners and
dull to a semi-gloss finish over time can hide the peroxide catalyst used in polyester and
some of the flaws that might otherwise mar vinyl ester resins and primers. The amines
an LPU finish. However, if the boat is perfect inhibit the action of the peroxide catalyst
and you are willing to spend the time and preventing cure at the interface. For this
care required to use LPU paints, she’ll even reason, it is not possible to “gel coat” cured
be more beautiful. epoxy without specialty barrier coats and it
is very risky to use peroxide cured polymers
Use any color you want so long as it is light. directly over cured epoxy resins. Besides,
If you paint with a dark color and the boat is gel coats don’t look all that good when
in the summer sun you are going to experi- applied to a male form. Their best use is
ence a number of problems especially if it is against a polished female mold.
a wood boat. First, you’ll get “print through”.
This is the telegraphing of the cloth weave Be sure to follow the paint manufacturer’s
pattern to the glossy painted surface. Second, instructions when doing the test patch. With
you’ll see what appears to be shrinkage of the exception of the high build two part
the epoxy resin (microballoon putty over epoxy primers, all finish paint systems
screw holes, for example). This is caused by should be applied thinly. Thick coats will
the expansion and contraction of the wood not dry properly and may take weeks to
fiber due to changing moisture content “through dry”. Temperature and humidity
rapidly aggravated by excess heat soaked play an important role in the speed of alkyd
up by your darkly painted boat. Finally, the paint drying. The higher the temperature
useful life of the boat will be shorter. and lower the humidity, the faster drying.

17

You can gauge drying by digging your
fingernail into your test patch and scratching. Troubleshooting
If the paint film is still soft below its surface
then it has not finished drying. A dry film is Following are questions we are commonly
hard all the way through. A simple test asked when something goes wrong. We
called the cross hatch adhesion test will show hope that you will read them because if you
how the new layer bonds to he substrates. Do have a problem the answer may appear
this test only on paint that has dried thoroughly. below. If it doesn’t then call us on our
To do this test, take an industrial razor blade technical line and we’ll go over it with you.
and score the surface with a set of 8 parallel
lines about an eighth of an inch apart. Score Problem: The epoxy has turned hazy and has
a similar set at 90° degrees from and crossing white material in the bottom of the jug.
the first set. The finished lines should look Cause and Solution: The epoxy is crystallizing
like a giant tic tac toe grid. Take some tan due to storage at too low a temperature. Heat
masking tape and press the sticky side into resin to 60°C until crystallization clears. You
the grid leaving a tail. Press the tape with the can do this by placing the material (enclosed
back of your fingernail. Grab the tail and jerk in its original container) in a hot water bath
the tape off the grid. Examine both the tape or in a black plastic bag in the sun.
and the grid for paint adhesion failures.
Except for the grid lines on the tape, no paint
should come off on the tape. If it does then Problem: The epoxy isn’t curing.
you have an adhesion problem and it WILL
Cause and Solution: It was mixed at the wrong
show up on your boat most likely in the form
ratio. Resin was mixed with resin or vice versa.
of paint blisters. Resand with a coarser grit
Remove the uncured material thoroughly by
or better, select a different substrate/top coat
scraping and solvent washing. Mix at proper
combination and test it.
ratio and reapply.
Once you are satisfied that there are no
system compatibility or adhesion problems Problem: The epoxy keeps going off in the pot.
then you can paint your boat with confidence.
Cause and Solution: The batch is too big or left
By this time you are probably wondering too long in the pot. The hardener is too fast for
why we don’t just give you a list of what the conditions. Use a smaller batch and get it
paint brands you can use. We would if we out of the pot sooner. Change hardeners.
could but because paint makers are free to
modify their formulations without notifying
Problem: The epoxy is still gummy.
Industrial Formulators we will not recom-
mend a specific brand of paint. The batch Cause and Solution: The ratio was wrong. It was
we test might have changed by the time inadequately mixed. Not enough time has
information about our results gets to you. elapsed at the curing temperature. Make sure
It is not possible for us to keep up with all that the gumminess is not just the amine
the different brands and lot numbers. blush. Wait and see if the cure proceeds.
Apply some heat if possible. If it is still gummy
then remove the uncured material thoroughly
by scraping and solvent washing. Mix at
proper ratio and reapply.

18

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Burnaby, BC
Canada, V5C 3H9

Technical Support: (604) 294-5723
FAX: (604) 294-8052
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