Putting a hold on leaks
By Christopher Perego,
BASF Construction Chemicals-Building Systems
Slamming the water
gate: Proper selection
and use of coatings,
sealants serve a central role
in shoring up the integrity
of the building envelope
Photo courtesy of Kellie L. Folkerts
ince the beginning of human history, people have been building shelter to pro-
tect themselves from the environment. Human intuition would suggest that
nothing beats a warm, dry bed. Intuition would also suggest that rain and
water belong on the outside of a building, not the inside.
Building design and materials have advanced greatly over time.
Construction materials such as concrete allow designers to create more
than just shelter, but buildings that deliver much more in the form of
durable, economic, aesthetically pleasing buildings. As greatly as build-
ing styles have varied over the years, one objective has remained con-
10 Journal of Architectural Coatings / June / July 2008
stant: the objective of keeping water spalls; loose rail posts; peeling paint; can encompass the entire building from
out of buildings. and efflorescence. Depending on the the footing to the roof system. This dis-
Concrete in all its forms (cast in nature of the building design, concrete cussion will focus on three areas.
place, precast, tilt wall) generally per- spalls and loose rail posts on balconies • Common problems related to sealant
forms well in the face of moisture; how- become serious public-safety issues and preparation and installation;
ever, concrete represents only one com- a significant liability for the building • Proper coating selection and applica-
ponent of the building envelope. While owner. tion; and
concrete participates with other materi- There is a saying in the construction • Common design- and construction-
als to provide a protective skin for the industry that goes, “Last on, first related issues that affect a building’s
structure, the concrete itself needs to be called.” This generally refers to the last protection against moisture.
protected from the effects of moisture. contractor to work on the exterior of
A building envelope is comprised of a the building. Often, this is the painting
variety of materials working together as contractor. Concrete buildings can leak Sealant technology has advanced over
a system to protect indoor environ- for many reasons; the wall coating is the years, but its primary purpose
ments from the elements—rain, snow, only one of these reasons. The list of remains the same: to prevent the pas-
and warm or cold air. Unwanted mois- potential issues is expanded by the vari- sage of air and moisture. The sealant
ture in a building can lead to a multi- ous types of building design and mate- plays a vital role in protecting a build-
tude of problems: water damage to the rials. This article will focus on some of ing from the ingress of moisture.
building and its contents; mold; poor the most common issues related to In the construction community, the
indoor air quality; peeling paint; and moisture protection for concrete build- terms “sealant” and “caulk” are used
damaged finishes. The implications for ings. interchangeably. While both types of
the exterior can be just as serious: cor- Moisture protection for concrete materials are used to prevent the pas-
rosion of reinforcing steel; concrete structures constitutes a broad topic and sage of air and moisture, sealants are
generally designed to accommodate materials. Thus, the ability to join dis- common cause of sealant failure is
differential movement greater than similar materials is an important joint preparation.
25%. Caulks are mainly used for aes- attribute of a sealant. Also, substrates Preparation will vary slightly by sub-
thetic and sanitary applications. For low in tensile strength, such as EIFS, strate, but the basic requirements
the purpose of this discussion, sealants require low-modulus sealants, which include the need for a clean, dry, and
will be the focus. reduce bond-line stress, minimizing sound surface. Implicit in this defini-
Sealants are used in numerous loca- failures. tion of “clean” is a condition that is
tions of the building envelope, such as Compatibility with residual free of contaminants. Contaminants
the following. sealant. Residual sealant is a reality in such as dirt, oil, and asphalt can be
• At expansion joints, for control of most restoration projects, so the introduced during the cleaning process.
expansion and contraction replacement sealant should be compat- Care should be taken to avoid these
• Where dissimilar materials meet, ible with any residual sealant. With a contaminants, as they will adversely
such as EIFS and concrete affect the performance of sealants.
• On window and door perimeters, The three most common methods of
where they provide a weather seal joint preparation involve the use of
around windows and doors compressed air, the solvent wipe, and
• On parapet caps, where they prevent mechanical preparation. Adhesive fail-
wind-driven rain from entering under ure is often traced back to improper
the cap cleaning of the joint. The following are
• At penetrations created by pipes, some common pitfalls of preparation,
conduit, anchorage, and signage along with recommendations to pre-
Differential movement occurs in vent problems.
areas where materials of different types Compressed air. Air should be free
meet on a wall. Movement also occurs of oil and water; an oil filter and mois-
due to the expansion and contraction ture trap should be used to eliminate
of materials such as concrete. Because contaminants. Oil introduced into the
the primary function of a sealant is to joint will affect adhesion, and moisture
accommodate differential movement, it introduced to the joint will affect cur-
is important to know and understand ing of most sealants.
the potential movement of the joint. Solvent wipe. This process consists
Example of coating that is not compatible with
The Sealant, Waterproofing & elastomeric sealant. Photos courtesy of BASF of wiping the joint with solvent. The
Restoration Institute (SWR Institute) Construction Chemicals-Building Systems. SWR Institute recommends the “two-
provides reference information to help rag method,” with the use of clean sol-
the specifier determine the proper size vent and frequent changing of rags to
and spacing of expansion joints.1 few exceptions, it is best to replace avoid spreading of contaminants in the
Best practice dictates that the width sealant with the same technology. joint. The sealant manufacturer should
of an expansion joint should be four Paintability. Elastomeric sealants be consulted for recommendations on
times the anticipated movement.2,3 move more than most paints and coat- solvents used to clean joints.
This design creates a safety factor for ings. Peeling paint over a sealant can Mechanical methods. These
joint performance and construction lead to further coating delamination, include wire brushing, blasting, grind-
erection tolerances. resulting in damage to the concrete. ing, and sawing, and are often the best
Sealant failure in expansion joints is Selecting a sealant that is paintable way to completely remove sealant
a primary source of moisture infiltra- minimizes the risk of failure. residue. Again, care should be taken to
tion in concrete structures. When avoid spreading contaminants through-
selecting a sealant, attention should be out the joint. Mechanical preparation,
given to movement capability and the however, is not appropriate for all sub-
following factors. It is widely accepted in the waterproof- strates and can void manufacturers’
Type of substrate. Building ing industry that the most critical fac- warranties on window and door frames
envelopes are composed of multiple tor in sealant application and the most and coated metal panels.
12 Journal of Architectural Coatings / June / July 2008
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Primers should be applied to joints as Protective wall coatings waterproof while still allowing our bod-
recommended by the sealant manufac- The building envelope of most concrete ies to perspire.
turer. Priming maximizes adhesion to buildings is considered a barrier wall. The ability of a coating to allow mois-
help keep the building watertight, and The exterior face of the building, ture vapor to pass is called permeability.
ensures adhesion to special substrates including seals, sealants, and wall coat- Vapor permeability is an important
such as coated metal panels. Primer ings, is designed to prevent the ingress issue that deserves and receives consid-
application might be viewed as inex- of moisture. We have discussed the role erable attention, but we will leave that
pensive insurance when weighed of the sealant in a barrier wall system. A discussion for another forum.
against the cost of a call-back. protective wall coating also plays an Permeability is only one of several
important role in preventing moisture important properties to consider when
Sealant installation selecting a coating.
The following steps should be followed The most common
when applying sealants. source of coating fail-
• The appropriate size backer rod (25% ure on concrete build-
larger than joint) is installed to the pre- ings can be traced to
scribed uniform depth. erroneous material
• A joint dimension twice as wide as selection—selecting a
deep, to a maximum ½-inch depth, is material that is not
recommended. alkali tolerant, or using
• The sealant is installed in a continu- a decorative paint in
ous bead, then tooled into the joint. place of a higher-per-
Tooling ensures a strong bond and elim- formance concrete
inates trapped air within the sealant. coating. While a num-
The SWR Institute recommends dry ber of differences exist
tooling, as tooling agents such as sol- between paint and
vents or soapy water can interfere with coatings, it is generally
the proper curing of a sealant or cause acknowledged that film
discoloration. build is one of the
Sealant inspection Thin-mil materials
Building construction is an imperfect (paints) typically range
science. As hard was we try, mistakes in dry-mil thickness
can be made, buildings can settle, and from 3 to 5 mils. High-
acts of God can prevail against the build materials (coat-
finest engineering. After all that can be ings) range in dry-film
done has been done, it is important to thickness from 10 to 20
inspect the façade, and particularly the mils. The difference in
sealants, on a regular basis. film build is primarily
Elastomeric sealants and high-build coatings play an imp ortant role
Minor issues related to sealants are related to the polymer
in p rotecting buildings from the elements.
easily and economically solved if they types employed in
are addressed early. If allowed to go thick-film coatings,
unchecked, however, they can allow ingress and protecting the integrity of which allow higher solids content with-
penetration of significant amounts of the concrete structure. out cracking of the cured coating.
water into wall systems, which can lead At the same time it prevents moisture The benefits that properly applied
to much more costly repairs in the from getting into the substrate, a pro- high-build coatings can deliver are
future. The old adage of “an ounce of tective wall coating must also allow numerous:
prevention is worth a pound of cure” is moisture within the substrate to • waterproof protection to concrete
no more true than in the case of façade escape.4 A coating functions much in structures;
inspection. the same way our skin functions: it is • protection from carbonation of con-
Journal of Architectural Coatings / June / July 2008 15
crete and ingress of chloride ions; ing reinforcing steel from corrosion. As costs often go unrewarded when struc-
• the ability of elastomeric types of long as the pH of concrete remains tures need to be recoated because an
these coatings to bridge moving cracks above 9, corrosion of the reinforcing inexpensive paint was used in place of a
of up to 1/16th inch wide; steel will not occur. Corrosion can occur protective coating, and the paint subse-
• encapsulation of aggregate for aes- prematurely when steel reinforcing is quently fails. Additionally, protecting
thetics and masking of surface imper- placed too close to the surface of the concrete from corrosion, carbonation,
fections; concrete. As carbonation passes through and chloride-ion ingress goes beyond
• toleration of the naturally higher pH the concrete, the steel becomes suscep- aesthetics to the heart of building life-
of concrete substrates; tible to corrosion at an earlier stage.5 cycle, and ultimately public safety.
• aesthetic appeal and color range Studies have shown that the applica-
equal to or greater than paints; and tion of high-build coatings can combat Surface preparation
• long-term service life. the carbonation of concrete.6 This abili- As is the case with sealants, proper
One of the most important benefits a ty to protect concrete from carbonation preparation is 90% of the battle in
high-build coating provides to a con- is dependent on the coating’s intrinsic ensuring the successful performance of
crete structure is protection from car- capacity to diffuse CO2, along with the exterior wall coatings. As most high-
bonation of the concrete and ingress of dry film thickness. Together, these two build coatings bond by means of
soluble chloride ions. Dilute carbon characteristics present a barrier that acts mechanical adhesion, surface prepara-
dioxide carried in rain, in addition to as simulated concrete cover over the tion is critical.
atmospheric moisture, lowers the nat- reinforcing steel. Frequently encountered surface-
ural alkalinity of concrete. This natural Concrete is a unique substrate with preparation issues involving concrete
alkalinity is actually beneficial, protect- unique requirements. Efforts to reduce buildings can be divided into two cate-
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gories: contaminants and surface the bond of wall coatings. It can often the concrete was cast in a form, steel-
imperfections. Common contaminants be removed by simple power washing, troweled, or broom-finished. A com-
include curing compounds, efflores- although stubborn stains may require mon misconception is that a broom
cence, form-release agents, and con- chemical cleaners. finish always provides a surface that is
crete laitance. Surface contaminants Form-release agents are used to aid in sound enough to receive a coating.
may act as bond breakers and inhibit the removal of concrete forms follow- Laitance should be removed through
the proper bonding of coatings.7 ing pouring of concrete. These agents abrasive blasting or water blasting.
Curing compounds are film-forming are often petroleum-based materials, Some common surface imperfections
acrylic membranes, wax-based emul- and leave a light, oily film on the con- include bug holes, tie holes, honey-
sions, or dissipating hydrocarbons that crete surface. This film must be combs, mortar fins, and cement
are used to aid in the curing of concrete removed before applying a wall coat- slurry.7
to facilitate the development of needed ing. Bug holes are small holes that devel-
properties. These compounds should be Concrete laitance is a thin layer of op on the concrete surface due to a
removed before high-build coatings are weak concrete paste on the surface of lack of consolidation of the concrete.
applied. Removal methods vary, the concrete, and is composed of High-build protective coatings are
depending on the type of curing com- Portland cement and “fines” carried to designed to be applied in a continuous
pound. the surface by bleed water. This layer film layer, but these holes create breaks
Efflorescence is a soluble salt pro- typically is characterized by a high in the coating. They should be proper-
duced as a byproduct of cement hydra- water-to-cement ratio, lacks cohesive ly prepared and patched in accordance
tion in concrete. Generally, laitance is strength, and is very friable. Laitance with ACI 301.
a crystalline substance that will inhibit can be present regardless of whether Tie holes are holes where anchors
once held the concrete forms together. lead to the formation of efflorescence ing on the type of structure, crack loca-
These need to be repaired, and should and, eventually, delamination of the tion, and aesthetic requirements.
be prepared and patched in accor- coating, exposing more of the sub- Window openings. Windows rep-
dance with ACI 301. strate. resent a common entry point for mois-
Honeycombs result from improper ture. Window sills are typically sloped
vibration and consolidation of the to allow moisture to be deflected away
concrete, and can also form below As long as humans continue to design from the window. A condition often
obstructions in concrete forms. They and build buildings, human error is observed on concrete buildings (cast in
often are irregular in shape and may inevitable. In many ways, concrete is place, precast, and tilt wall) is the pres-
be obscured by a thin cover of mortar an ideal construction material—it is ence of flat window sills. This allows
over voids. These voids need to be versatile, economical, and durable. It water to collect and potentially find its
opened up and repaired per ACI 301. can, however, present some challenges way to the building interior. Horizontal
Left untreated, they can crack beneath that affect the building envelope’s surfaces require different coating mate-
the coating, causing delamination. capacity to resist moisture. These chal- rials in order to perform properly. This
Mortar fins occur when cement paste lenges can affect the performance of adds cost and complications to the pro-
finds its way into gaps between con- the wall system as well as the wall ject.
crete forms. Fins or ridges cause high coating and sealant. Sealant width-to-depth ratio.
spots in an applied coating, and can Moisture resistance in the building While this concept is simple, it remains
result in the application of a too-thin exterior can be compromised in a common to find the wrong-sized
coating film over these ridges. Fins number of ways and at various parts of backer rod doubled up to fill a larger
should be ground flush with the sur- the exterior. These are reviewed in the joint. This configuration leads to
rounding concrete, per ACI 303. following discussion. restraint within the sealant, almost
Placement of reinforcement. always resulting in cohesive failure. It
Application considerations Steel reinforcement placed too close to is also common to find sealant
The most common application issue the finished surface can result in pre- installed too deep. This can lead to
related to high-build coatings is film mature corrosion of the steel reinforce- cohesive or even adhesive failure, as
uniformity. When properly applied, a ment, leading to spalling of the con- the deep-set sealant bead places so
high-build coating provides a continu- crete. ACI 301 requires that steel be much stress on the bondline that the
ous layer of protection over the exteri- covered with at least two inches of bonding forces are overwhelmed.
or of the building. As is the case with concrete. If an insufficient concrete Parapet details. On precast or
fluid-applied waterproofing for below- cover is recognized before the building cast-in-place buildings, parapet caps are
grade applications, high-build protec- is put into service, a high-performance often eliminated. The expansion joint
tive coatings for above-grade settings coating may be applied to the concrete is carried up the wall and over the top.
should be applied at a uniform thick- to protect it from early carbonation This is an area that often is prone to
ness, with assurance that pinholes and and steel corrosion. leaks. Best practice would dictate
other coating defects do not occur. Cracking. The concrete industry installing a parapet cap at the top of
High-build coatings work together has made great strides in the formula- walls. Parapet caps, however, also can
with the other elements of the wall tion and installation of concrete to serve as a common point of entry for
system to provide a barrier of protec- minimize cracking; however, cracking wind-driven rain. Caulking on the
tion for the building. The presence of still occurs in both precast and cast-in- underside of the hemmed edge of the
pinholes, holidays, and skips in the place concrete. Cracks provide an parapet cap, though a good practice, is
applied coating can be likened to holes avenue for moisture, oxygen, and chlo- often overlooked or omitted. Lastly, the
in the bottom of a boat. These voids rides to reach the reinforcing steel. back of the parapet wall should be
not only allow moisture to penetrate This can accelerate corrosion of steel coated. A good practice is to bring the
the wall system, but also provide an reinforcement, induce concrete roofing material up the back of the
avenue to carbonation and chloride- spalling, and lead to premature deteri- parapet wall and terminate it under the
ion ingress. Additionally, pinholes and oration of wall components, including parapet cap. More often than not, it’s
holidays allow moisture to migrate anchors, drywall, and interior finishes. what you don’t see that causes most of
behind the wall coating, and often Treatment of cracks will vary depend- the problems.
18 Journal of Architectural Coatings / June / July 2008
The role of mock-ups advantage of also showing the full pro- In addition to mock-ups, job-site vis-
It is important to verify compatibility of file of the sealant and is commonly its from qualified manufacturers repre-
materials before work commences. used to evaluate mockups, the non- sentatives can help prevent problems
While previous experience is a good destructive test may be more practical before they occur. Manufacturers work-
indicator, it is best to install a mock-up for ongoing inspection during the pro- ing with the contractor to address
on the job site with the actual materials ject.8 preparation and application questions
that will be used on the project. Paint Coatings mock-ups provide a repre- can help ensure that what is specified is
formulations for coated window frames sentative example to the owner and what is used on the project.
Melding the parts
can change over time. Where a sealant specifier of the final aesthetic of the
to create the whole
once adhered well, it may now require coating. It also helps the contractor
additional surface preparation or a dif- determine the application method
ferent primer. needed to achieve a pinhole-free film. This article has sought to identify and
A field mock-up for sealant adhesion Wall-coating mock-ups protect all par- discuss some of the more common
involves preparing the joint, installing ties involved. Memories quickly fade, issues related to moisture protection of
the backer rod and sealant, and then but mock-ups can serve as the ultimate concrete buildings. Specifically, the dis-
allowing the sealant to cure. ASTM arbiter in any questions or conflicts cussion has focused on issues related to
C1521 provides both destructive and involving failures. Mock-ups should be selecting and installing elastomeric
non-destructive procedures for evaluat- applied on an inconspicuous area of the sealants and selecting and applying pro-
ing the adhesion of sealants in the field. building and remain there until coating tective wall coatings.
While the destructive test has the application has been completed. Together, sealants and wall coatings
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Journal of Architectural Coatings / June / July 2008 19
combine to form a barrier of protection providing waterproofing protection for a system to protect occupants from the
around concrete buildings. They protect building exteriors, high-build coatings forces of nature: wind, rain, heat, and
buildings from the negative affects of protect concrete buildings from the cold. These components are designed by
moisture ingress, including water dam- detrimental effects of carbonation and professionals and installed by skilled
age to building elements and its con- chloride-ion ingress. trades.
tents; mold; poor indoor air quality; Building envelopes are composed of a While many common problems that
and damaged finishes. In addition to variety of materials working together as can compromise the performance of a
building envelope have been observed
in the field, these problems and failures
are not inevitable. Proper material selec-
COAT tion, surface preparation, and material
installation, along with the use of job-
SG SERIES ANTI-SLIP COATINGS
site mock-ups and post-installation
inspections, can ensure that the build-
ing meets the primary objective that
has remained constant over the cen-
turies: keeping water out of the struc-
3. ACI 504 R90 Guide to Sealing Joints
in Concrete Structures.
when the going gets tough... 4. ACI 515.1R-29 A Guide to the Use of
we get tougher. Protective, and Decorative Barrier
Systems for Concrete.
5. ACI 224 Causes, Evaluation and
Foot trafﬁc, vehicle trafﬁc, heat, cold, the relentless effects of Repair of Cracks in Concrete
weather... With these kinds of forces stacked against you, it’s Structures.
essential to have a coating that can rise to the challenge - one
6. Hurley, Shaun A., “The Long-Term
that you can have conﬁdence in to remain strong and effective
Durability and Performance
no matter how hard you use or abuse it.
Assessment of Coated Concrete,”
Wearcoat ﬂoor coatings deﬁne durability. Easy to apply, easy to
ings durability. apply,
ply Journal of Protective Coatings and
clean, non-slip and incredibly tough, Wearcoat® will give you the
cr Wearcoat ve Linings, September 2000.
edge you need to get the job done - safely and efﬁciently. Call us
ntly 7. Holl, Charles H, O’Connor, Scott A,
today or check us out on the web. Our expert staff is ready to
t expert staff ready “Cleaning and Preparing Concrete
help with any coating needs you have... before Repair,” Concrete
International, March 1997.
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8. ASTM C1521-02a, “Standard Practice
COATINGS FOR INDUSTRY, INC.
TR for Evaluating Adhesion of Installed
Call us today – 215-723-0919 Fax 215-723-0911
y 9 215-723-0911
15-723-091 Weatherproofing Sealant Joints”,
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Serving the concrete ﬂooring, structural steel,
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transportation and aerospace industries for over 35 years.
20 Journal of Architectural Coatings / June / July 2008