Epoxies are structural repair polymers offering permanent repair of concrete. This brief discussion focuses on tips for success with epoxies including handling, safety, applying, mixing, surface preparation, environmental factors and other considerations for successful repair. It is oriented towards the professional concrete repair specialist contractor.

1. 25 INCREDIBLE TIPS
FOR CONCRETE REPAIR
WITH EPOXY
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2. 1. Surface prep is vital
As in many other construction activities, taking proper steps
to properly clean and prepare surfaces prior to the use of
repair materials is critical to the time efficiency and long term
success of your repair. Surface preparation methods include
(from gentle to aggressive) detergent scrubbing, acid etching,
grinding, abrasive blasting, steel shotblasting, scarifying, needle
scaling, high pressure water blast, scabbling, flame blasting,
bush hammering and milling/ rotomilling.
Note that some abrasive methods may leave a thin film of
dust on the surface which should be flushed with a high
pressure water blast. For protective coatings, often a
shotblast is the best first step with
the goals of removing all
contaminants, opening pores and
light cracks and providing a
roughened surface profile resembling
40 grit sand paper (such as ICRI CSP
3). For spalls and crack repair, it is
essential to remove all concrete
laitance, surface contaminants and
traces of form or release oils and
curing compounds using some form
of abrasive removal.
If you are considering pressure
washing, 5000 psi has been
From Concrete Intl, v 84, No. 6, 2012
determined as the minimum pressure
to provide acceptable levels of
cleaning of concrete surfaces. In cases where the cementitious surface was overworked
when placed or excess water was used, it is highly recommended that the paste layer be
partially or completely removed for the optimum performance of the repair. Applicable
specifications include: ACI 503R, ASTM 4263, ASTM 4260, ICRI 03732 and ICRI 310.2.
2. Elcometer tab pulls
Even with the best surface preparation (and a small
mock-up), unexpected issues can interfere with good
surface bonding. For a small investment, you can test the
bond of any repair material or coating in suspect areas
relatively quickly using small circular metal tabs. The
whole process is explained in ASTM D4541, a test
handled by an Elcometer 106 portable pull tester.
Consider that this test has been known to have
reproducibility issues, so use plenty of dollies in your evaluation. You can also make a
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3. home-built version that uses 2” diameter pipe caps (ground flat) and an Enerpac®
hydraulic cylinder (if you elect this option, have a third party check the calibration).
3. Provide a mockup when feasible
This preconstruction step demonstrates that you are willing to take the extra care to
ensure a quality project. This tactic is especially useful if you are planning to use a new
material. Disagreements should be minimal when the actual appearance is presented
before the project starts. Sometimes, you can be compensated for your time and
materials.
4. Save $ with local aggregates
For polymer repair mortar or grouts, many (if not
most) manufacturers package their aggregate filled
systems in a 3 package system which includes bags
or pails of graded sands. Unfortunately, shipping a
low cost and dense product such as sand around
the country or overseas is very costly and we don’t
think that it is necessary. So call us when you
develop a requirement for this type of a system and
we’ll provide recommendations to locally source a
gap graded aggregate system that can provide
significant savings for you and your customer. Use
only dried sand (less than 0.2% moisture) in
polymer mixes.
5. Estimate with a waste factor margin
For most of the repair jobs (not counting coatings) where epoxies and other polymeric
products are used, the material cost is typically within a range of 5-10% of the total job
costs which include other materials, equipment, mobilization and labor. So if you
estimate conservatively and your guys run short, there may be several negative
consequences.
First, the guys might shortcut the application rate which might undermine the
performance of the areas that were short. Second, they might run out and call you on
late Friday afternoon looking for a very costly delivery by air on Saturday, or your crew
might have to re-mobilize because the owner needs the area back in service while
awaiting the replacement material. There isn’t much cost risk in buying a little extra as
epoxies are very long-lived materials so you can use them on future projects or return
them in unused condition (we charge a 15% return fee). Plus, if you elect to buy a little
extra material, you likely just saved a lot more on your most expensive cost item which
is labor. Finally, if your guys discover a bit of extra work not originally noticed, you have
an option for a change order without excessive costs.
6. Operate safely
Maintain copies of all MSDS (now called SDS in the new global
harmonized system) to be easily accessible on site. Don’t
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4. assume that because you’ve worked in the industry for 30 years that the content of the
MSDS is the same as in 1982—they are frequently updated and the contents are subject
to change. For example, in the case of accidental ingestion, syrup of ipecac is no longer
routinely suggested.
Make sure that your guys wear the proper PPE even in hot/humid weather. The
minimum level of protection for handling chemical polymers for concrete repair typically
includes long sleeves, long pants, rubber gloves and safety glasses (with side shields).
Other levels of PPE can include face shields, goggles, Tyvex® or other synthetic outer
clothing, dust and organic vapor masks and hearing protection. PPE training should
ensure the technician knows how to remove it without contaminating himself so a trip
to the washroom or food trailer doesn’t mean more exposure. In some individuals,
certain chemicals can cause an allergic sensitivity that can be triggered over repeated
exposures and make working in the field impossible. Encourage your employees to clean
their work clothing regularly rather than allowing contaminants to build up. Finally, don’t
assume your guys will think about drinking sufficient water on the hottest days—you will
have to keep reminding them.
7. Soap and water vs. solvents
For cleaning epoxies and other polymers from tools, many field
techs use acetone or MEK. If there are only minor amounts of
product to be cleaned and the bulk material is uncured, you can
squirt a bead of liquid dishwashing soap right on the tool surface
and rinse off the blade or surface with hot running water. Many of
the polymers will emulsify and rinse off if you use a little extra
concentrated soap which is far less costly (and never flammable) than solvents. The
same technique works on cleaning any exposed skin—liquid detergent is better for your
skin than acetone. Some contractors swear by film forming liquid skin protectant creams
for the times when the gloves are off.
8. Save cardboard
Instead of disposing of large cardboard shipping cartons, have your warehouse guy save
them and cut them into 12”x12” (or some other favorite size) squares to use as mixing
platforms for small quantities of 2 component polymers or for making small paste mixes.
When the project is over, you can toss the cardboard as the epoxy scraps should be in
the hardened form of a cured plastic.
9. Always take pictures
Your project site pictures could have a value far in excess of 1000
words. It should be an absolute requirement that your foreman
takes shots before and after every job. These can help in many
ways: establish baseline conditions, provide visual backing for change
order situations, assist in accident investigations, provide evidence of quality work and
project completion, are valuable for marketing and establishing credibility and to help
educate new employees.
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5. 10. Timing an industrial floor or concrete deck
Plan your projects so the prepatory steps take place in the
morning. Avoid placing impermeable coatings (includes most high
solids epoxies and polyurethanes) during periods of rapidly rising
temperatures which is usually morning to early afternoon
(especially in situations without climate controlled environments).
In most areas, the daily temperature cycle has reached its
maximum around 3-4 pm (15-1600 hours) so this is a great time to
start the coating. This late day timing minimizes the potential for high rates of vapor
transmission to interfere with the success of the coating. If the building has a functional
heating/cooling system, the air conditioner should be run for at least 2 days prior to the
coating to minimize the same issues.
11. Don’t wait 30 days
We offer several primer solutions for bonding, repairing or coating green concrete
including QuikPrime which even works underwater. You can generally use CCS Coating,
QuikPrime 24 hours after concrete placement.
12. Hammer your concrete
Don’t attempt to fix delaminated concrete without
confirming the extent of the problem. Bring a sounding
hammer and test the area to be repaired. A heavy steel
chain can also be used. Cracks and spalls will sometimes
be caused by poorly bonded topping slabs or old repairs
which have disbonded or never bonded over the original
damaged substrate. Concrete can debond from steel in
elevated slab on pan installations. If the concrete is
delaminated in areas, fixing the cracks without repairing
the underlying delamination is a waste of time. Be
prepared to consider the cause(s) and offer a fix for the
delamination as first steps in the repair.
13. Heat is speedier
Most ambient temperature cure epoxies exhibit reaction rates that increase or decrease
by a factor of 2 for every 18°F or 10°C change in temperature. So if your epoxy repair
material is curing too slowly, gently add heat to speed cure times. There are many
techniques for heating which include: heat guns, warming blankets, pre-heating the cans
of epoxy before use, warming the substrate with local baseboard heaters contained with
temporary walls of plastic sheeting, etc. It’s best to use temperatures below 300°F
(150°C) for speed curing (this includes heat guns). Also since epoxies react by giving off
heat (in an exothermic reaction), the thicker you apply an epoxy, generally, the faster it
cures. Conversely, if your summer temperatures are very hot, the amount of useful life
of epoxy mixes may be too short for practical use. In this case, cooling the separate
components before use in an ice bath or air conditioned area will help extend the mixed
life.
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6. 14. Get thinner with heat
If your epoxy is too thick, preheat the components before mixing. Store them overnight
in a closet with a portable heater or put them in the cab of the truck with the heater
turned up when it’s cold outside. Some field technicians mount a light bulb inside their
epoxy injection pump to warm the epoxy in the reservoirs. An epoxy with a viscosity of
1000 cPs at 50°F might have a viscosity of only 150 cPs at 80°F. Don’t forget that useful
(mixed) lives and cure times are also affected by temperature.
15. Polymers shrink
Epoxies and other polymers have a secret property that is rarely discussed. When A +
B components are mixed in proper proportions, most polymers exhibit both linear and
volume shrinkage upon cure. This is because the newly formed cross linked polymer
takes up less space than the separate unreacted components. Shrinkage is factor that
must be considered when the use of repair polymers might involve a thick cross-section
of cured material.
So, how thick is too thick before you will develop a problem such as internal stresses in
the repair? The answer is that it depends on the specifics. There are some tactics which
include the use of installing multiple lifts, low exotherm and/or low modulus resins and
aggregate filled systems which help alleviate problems when thicker cross-sections of
repair materials are needed. Please call us for advice.
16. Polymers move more
In addition to shrinkage, remember that most concrete repair polymers including
epoxies have a thermal coefficient of expansion that is greater than that of other
substrates such as concrete or steel. How much different varies with the polymer but it
would be fair to say that the polymers expand or contract with heat about 5-10 times
more than concrete or steel over the same temperature change. This is another factor
to consider when placing large cross-sections of polymer repair materials. Call us for
specific advice.
17. Moisture vapor can drive you crazy
Standard practice for concrete floor construction today is
to install a vapor barrier between the structural slab and
underlying compacted earth or engineered fill. This
practice is relatively new, so what can be done with older
concrete floors which don’t have a vapor barrier? Today,
if your moisture test shows 3 lbs/1000 sq. ft/24 hrs or
more (ASTM F18690), don’t even think about installing an
impermeable coating or flooring material without first using an epoxy vapor barrier.
We make a great product for this purpose called MVR Coating. When properly used, it
will reduce the vapor drive to a safe level and can be recoated in about 12 hours.
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7. 18. Width matters
Before embarking on an epoxy crack
injection repair, get a good idea of the
average width and depth of the cracks. How?
You can start with using a plastic crack card
and graduate to a lighted portable crack
scope. Remember that for smaller projects,
you will consume more epoxy by flushing the
gun and cleaning that probably will be used in
the cracks. So on smaller projects, your
waste factor can be over 50%. Don’t be
caught short on materials.
19. Roll your ports
Surface ports have become a popular tool to use with epoxy
injection. Yet, they can also lead to poor performance on
these projects if they are plugged or fall off in use. When
placing ports with a paste adhesive, it is critical that the
adhesive doesn’t plug the barrel of the port over the crack.
Some contractors have found that mixing their paste adhesive
on a piece of cardboard and then rolling the flange of the port
through the adhesive (rather than using a trowel to apply
paste) works best. Others insert a cocktail straw or
toothpick into the port to hold it in place and ensure
continuity into the crack.
20. Epoxies last longer
When your project is complete, don’t automatically react off your leftover A and B
components to dispose of partial containers of epoxy. Most epoxy products are
relatively stable and can be used for extended periods if kept within a reasonable
temperature range and sealed. We say that most of our epoxy products can be safely
used within 3 years of manufacture. There may be some settling (particularly for
coatings) but the products will still perform if the separate components are mixed well
before use. Caution: moisture sensitive materials such as polyureas or polyurethanes
have a much shorter shelf life.
21. Cosmetic surgery for concrete
Say you have a sound substrate with a myriad of different tones or slight cracks or chips
that disturb the smooth face. What can be done? Consider sacking, a repair technique
that involves pre-wetting the substrate and then hitting the surface a burlap sack
containing fine aggregate of the same color as the concrete along with some Portland
cement. A fine wet cement based slurry can also be applied by heavy brush. This trick
can also rid the substrate of the dark crack “shadow” following epoxy crack injection on
architecturally sensitive surfaces such as light precast panels—call us for more
information.
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8. 22. Bulk loaders work for epoxy too
Contractors who specialize in caulking and waterproofing
may use bulk loaders to shoot single component
elastomeric caulks. For delivering both liquid and paste
viscosity epoxies, bulk loaders come in a wide variety of
gun types and applicator tips including battery and
pneumatic operated. They can be used with two
component epoxies as long as the mixed material has an extended potlife. The biggest
reasons to consider a bulk loader are time and material savings—they can easily loaded
from a bulk mix in a 5 gallon bucket, placed just where needed and products sold in bulk
are less costly. For larger projects, air-driven two-way bulk loaders might offer
additional efficiency. Albion Engineering is a great place to look for a wide selection.
23. Use a scale
On all of our data sheets, we include the separate weights of
parts A and B. Why? We have noticed many other
manufacturers require that all of the materials in multiple
containers be used to make a mix. Yet, we know that not
every project needs all of the materials in our containers and
we hate wasting good materials. Of course, you can also judge
proper quantities by filling clear plastic measuring cups or pails,
but the safest way to reproducibly get accuracy is to pre-weigh
both components since the weight is not affected if the
container becomes too dirty or colored to read the volumes on the sides. Just
remember that a material which is 2:1 by volume is not likely to have the same ratio by
weight.
24. Join up
ACI and ICRI are international members-driven
organizations where you can meet in local chapters or
attend regional or national conventions twice a year to
learn more about concrete and its repair. Many of the attendee members have been
performing the same specialized concrete repair specialities and are happy to share
success stories.
25. Come to our class
We organize free training sessions in structural concrete repair
and epoxy injection at least two or three times a year—they take
a day and a half. Call or email us if you’re interested.
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