Common concrete problems include surface scaling, cracking, dusting, popouts, efflorescence, crazing, blistering, plastic shrinkage, and issues specific to stamped concrete. Most problems stem from errors in finishing, using low-quality materials, inadequate curing, and improper placement. While unavoidable in some cases, most concrete issues can be prevented or reduced through best practices in mixing, placing, finishing, and curing concrete.

1. CONCRETE PROBLEM AND CAUSES
Concrete is an excellent material, but it is not perfect. You don’t have to look very far
to identify the real life concrete problems listed below. However, most of these
problems are avoidable, or fixable. There are way to many variables in the
production, mixing, placing, and finishing of concrete for me to discuss in detail.
Unfortunately, most concrete problems are the result of error with the finisher you or
the builder chooses. And builders, to maximize profit, take the lowest bidder. And in
my experience, so do many homeowners. The lowest bidder uses the least amount of
manpower to get the job done, and uses cheaper, lower quality concrete with low
compressive strengths and inexpensive admixture fillers (fly-ash). Most problems
associated with concrete arises from the inability of the finisher to finish the concrete
slab correctly, because of production rates and low manpower. I have examined
warranties offered by many homebuilders, and short of the concrete self-destructing,
most concrete defects are not covered. Therefore, builders get away with their
practices, and you are left dealing with concrete problems long after your home has
been built.
These are the most common problems associated with concrete. Every one of these
problems is either corrected, prevented, or reduced with the installation of our
polymer modified cement overlay.
Surface Scaling/Spalling
Surface scaling is when the surface of hardened concrete breaks off to a depth of
1.5mm to 5mm, generally during the first year of placement. This occurs because of
application of calcium or sodium chloride deicing salts on concrete with inadequate
strength, air entrainment, or curing. Unfortunately, as an end user, you may have no
control over these factors. Concrete that is subjected to use of deicing salts combined
with freeze-thaw conditions are prone to scaling. The National Research Council’s
Strategic Highway Research Program tested deicing salts to see how they would etch
and destroy concrete. The tests were interesting. It appears that magnesium chloride
did the least amount of damage. Calcium chloride caused 26 times more damage to
the concrete than magnesium chloride. Regular rock salt, sodium chloride, caused an
astonishing 63 times more damage. If the tests were accurate, it appears that it may be
worth the extra money to purchase and use magnesium chloride. Even still, your
driveway will track rock salt from the roads, and it will concentrate in your garage
where the snow/salt slurry collects and evaporates. Chemicals such as ammonium
nitrate and ammonium sulfate, which are components of most fertilizers can cause
scaling as well. Scaling is most common in concrete with poor surface strength,
caused by finishing a slab while bleed water is on the surface, or overworking the
surface resulting in a lower air content. Air entrainment is vital for concrete slabs
placed where freeze/thaw conditions exist. When scaling occurs, so does the blame
game. The homeowner blames the concrete finisher, the finisher blames the
homeowner or the redi-mix company. The mix company blames the finisher

2. Cracking
This one needs little explanation. Cracking is breaks that occur in areas other than
those placed intentionally. Almost everyone has cracks in their concrete, and because
there are so many reasons why concrete cracks, it is often impossible to know the
exact cause. The good news is, cracks seldom result in structural problems. Some of
the many reasons concrete cracks include:
Excess water in the mix.
A lot of water is not needed to allow concrete to cure. However, builders add extra
water to make it easier to finish out the concrete before it dries, because there are not
enough people available to do the job correctly. As concrete dries the slab will shrink
as excess water evaporates. This shrinkage literally pulls the slab apart.
Rapid drying of the concrete
The chemical reaction, which causes concrete to go from the liquid or plastic state to a
solid state, requires water. This chemical reaction, or hydration, continues to occur for
days and weeks after you pour the concrete. You can make sure that the necessary
water is available for this reaction by adequately curing the slab.
Improper strength of concrete for the job.
Unknown to many people is that concrete comes in different strengths, and can have
fiber mixed with the concrete to add to its strength. The Roman Coliseum was built
with fiber reinforced concrete and is still standing today. A pueblo house built in 1540
with straw reinforced adobe brick is believed to be the oldest house in the US.
Improperly placed tension control joints.
Plain and simple, concrete cracks because there is a stress on the concrete that
exceeds the tensile strength of concrete at any given point in time. The use of tension
control joints are placed to help alleviate those stresses. Many finishers have a lack of
understanding about where control joints should be placed. Improperly placed, or too
few control joints will mean the slab will crack to alleviate those stresses. The saw
cut, or tooled control joints are placed to provide an area for a controlled crack,
because once they are in place, the concrete will eventually crack in those places.
This prevents unsightly cracks elsewhere.
There is a popular misconception that the use of steel reinforcement bar (rebar) will
prevent cracks. It will not. However, rebar will hold a slab together that has cracked
and reduce shifting and heaving.
There isn’t a single concrete contractor that has never had to deal with their concrete
cracking. Sometimes, no matter what you do, problems will arise that were not seen
before the job started.

3. Dusting
Dusting is the presence of a powdery material at the surface of a hardened slab. A
concrete floor dusts under traffic because the wearing surface is weak. This weakness
can be caused by the finishing operation performed over bleed water on the surface.
Finishing or working this bleed water back into the top of the slab produces a low
strength layer right at the surface. Placement of concrete over poly or some non
absorbent surface, increases bleeding and as a result the risk of surface dusting.
It is caused by insufficient or no curing of the surface. This omission of curing often
results in a soft concrete surface, which will easily dust under traffic. In cold weather
the concrete sets slowly, particularly cold concrete in below grade placements. If
relative humidity is high, water will condense on the freshly placed concrete. This
water condensation, if troweled into the surface, will cause dusting.
Popouts
A popout is a conical shaped fragment that breaks out of the surface of concrete.
Popouts are usually caused by the expansion of porous aggregate particles having a
high rate of absorption. As the offending aggregate absorbs moisture or freezes under
moist conditions, its swelling creates internal pressures sufficient to scale the concrete
surface. Ironstone, coal, shale and soft fine grained limestones are the commonly
observed causes of popouts.
Most popouts occur within the first year of concrete placement. Moisture induced
swelling may occur shortly after placement due to moisture absorption from the
plastic concrete, or they may not occur until after prolonged rainy weather or the first
winter. Popouts are generally considered a cosmetic flaw primarily affecting the
concrete appearance and usually do not affect the service life of the concrete.
Efflorescence
Efflorescence is a crystaline deposit on surfaces of concrete. It is whitish in
appearance, and is sometimes referred to as “whiskers”. Efflorescence has been a
problem for many years, and is a topic of much controversy. The formation of these
salt deposits are not mysteries. They are, for the most part, water-soluble salts that
come from many possible sources to mar and detract from an otherwise beautiful and
serviceable structure. First of all, there must be water present to dissolve and transport
the salts. Groundwater is often a source of efflorescence. For water to carry or move
the salts to the surface there must be channels through which to move and migrate.
The more dense the material, whether it be brick, stone, stucco or concrete, the more
difficult for the water to transport salts to the surface. Conversely, the more porous the
material, the greater the ease with which salts are transported and deposited. Salt-bearing
water, on reaching the surface of a structure, air evaporates to deposit the salt.

4. Crazing
Crazing is the development of a fine network of random cracks on the surface of
concrete caused by the shrinkage of the surface layer. Generally, these cracks develop
at an early stage and are evident the day after placement or within the first week.
Crazing does not affect the structural integrity of the concrete and rarely affect the
durability or wear resistance.
Crazing is caused by poor or inadequate curing, an excessive concentration of cement
paste and fines at the surface caused by an overly wet mix, which allows coarse
aggregate to settle, bullfloating or finishing while there is bleed water on the surface
or the use of a steel trowel sealing the surface and diluting the cement paste.
Sprinkling cement on the surface to dry up the bleed water is a frequent cause of
crazing surfaces. This concentrates fines on the surface.
Blistering
Blisters are hollow, low profile bumps on the concrete surface typically ranging from
the size of a dime up to an inch, but occasionally 2 or 3 inches in diameter. The most
common cause is when a dense troweled skin of mortar about 1/8 inch thick covers an
underlying void which moves around under the surface during troweling. Blistering
can also be caused by troweling too soon; resulting in the surface being sealed too
early while the underlying concrete is plastic and bleeding or able to release entrapped
air.
Plastic Shrinkage
Plastic shrinkage cracks appear on the surface of a freshly placed concrete slab during
finishing operations or soon after. Plastic cracks are usually parallel to each other,
between 1 and 3 feet apart, and do not cross the perimeter. High slump concrete
increases shrinkage. Excess water can be expected to increase shrinkage
approximately in proportion to its percentage of the total mix water. Vapor barriers
are a key contributor to plastic shrinkage cracking. All bleed water must migrate to
the surface, which seriously affects timing, and surface set control methods.
Stamped Concrete Issues
There are additional problems conventional stamped concrete contractors must have
knowledge of in order to avoid failure of their finishes. These problems are non-issues
with polymer modified cement overlays. They are:
* Air entrainment–Low air entrainment that results in spalling and scaling of the
surface destroys decorative finishes. When dry-shake color is used, scales typically
have color on one side and plain concrete bonded to the colored layer on the back side

5. of the scale. This is because dry shake color hardeners provide a densified layer that
effectively protects the colored layer from freeze-thaw damage. When air entrainment
is excessively high, strength goes down, and there is virtually no bleed. It can also be
difficult to properly “wet out” dry shake color hardeners.
* High water-cement ratios–Because of the more porous surfaces that result from too
much water, colored finishes, including chemical stains, diffract more light, giving the
impression of weaker coloration. Due to the weaker surface, traffic wear patterns can
develop. In the case of chemical staining, wear can remove the colored layer.
* Lack of curing–These symptoms can be similar to high w/c ratio conditions. Un-hydrated
cement does not develop calcium hydroxide, so there is less of it for some
decorative products to react with. Colored surfaces will appear less intense than well-cured
concrete with the same amount of color. Stained surfaces also appear less
intense. Dusting and traffic wearing patterns problems can also result. However, most
decorative finishes can’t tolerate the same curing methods used for plain concrete.
* Low strength–When there isn’t enough cement paste in a mix, integral color isn’t
properly restrained in the paste, and color can be lost from the surface. Chemical
stains may not have enough calcium hydroxide to react with, resulting in less
coloration. Low strength in decorative finishes can cause traffic to wear into the
finishes.
* High moisture levels in concrete–Chemical stains react differently in areas of a slab
that have higher relative humidity. Decorative treatments, which do not have good
moisture vapor transmission properties, can peel off the surface, blemish, turn cloudy
white, or cause blisters to develop.
* Cold weather conditions–Long initial set times and excessive bleed water mean that
more calcium hydroxide comes to the surface where it reacts with carbon dioxide
from the air to form efflorescence. More laitance also comes to the surface from silica
in the aggregates, causing hard white silicates to form. Also, slab finishes are often
wet in appearance. In cold weather, concrete is usually covered with curing blankets
or plastic, causing unsightly efflorescence markings.
* Hot weather conditions–When conditions are really hot, there is less time to perform
all the added steps needed for some decorative finishes. In the case of stamped
concrete it is more likely that impressions will be “mushy” at the beginning of the
stamping process and too light, with little texture, at the end.

6. of the scale. This is because dry shake color hardeners provide a densified layer that
effectively protects the colored layer from freeze-thaw damage. When air entrainment
is excessively high, strength goes down, and there is virtually no bleed. It can also be
difficult to properly “wet out” dry shake color hardeners.
* High water-cement ratios–Because of the more porous surfaces that result from too
much water, colored finishes, including chemical stains, diffract more light, giving the
impression of weaker coloration. Due to the weaker surface, traffic wear patterns can
develop. In the case of chemical staining, wear can remove the colored layer.
* Lack of curing–These symptoms can be similar to high w/c ratio conditions. Un-hydrated
cement does not develop calcium hydroxide, so there is less of it for some
decorative products to react with. Colored surfaces will appear less intense than well-cured
concrete with the same amount of color. Stained surfaces also appear less
intense. Dusting and traffic wearing patterns problems can also result. However, most
decorative finishes can’t tolerate the same curing methods used for plain concrete.
* Low strength–When there isn’t enough cement paste in a mix, integral color isn’t
properly restrained in the paste, and color can be lost from the surface. Chemical
stains may not have enough calcium hydroxide to react with, resulting in less
coloration. Low strength in decorative finishes can cause traffic to wear into the
finishes.
* High moisture levels in concrete–Chemical stains react differently in areas of a slab
that have higher relative humidity. Decorative treatments, which do not have good
moisture vapor transmission properties, can peel off the surface, blemish, turn cloudy
white, or cause blisters to develop.
* Cold weather conditions–Long initial set times and excessive bleed water mean that
more calcium hydroxide comes to the surface where it reacts with carbon dioxide
from the air to form efflorescence. More laitance also comes to the surface from silica
in the aggregates, causing hard white silicates to form. Also, slab finishes are often
wet in appearance. In cold weather, concrete is usually covered with curing blankets
or plastic, causing unsightly efflorescence markings.
* Hot weather conditions–When conditions are really hot, there is less time to perform
all the added steps needed for some decorative finishes. In the case of stamped
concrete it is more likely that impressions will be “mushy” at the beginning of the
stamping process and too light, with little texture, at the end.