EPOXY
COATINGS 101
WHAT KIND TO USE AND WHEN
Epoxy Coatings 101: What Kind to Use and When
1
TABLE OF CONTENTS
Epoxy Coatings 101:
What Kind to Use and When_____________________ 3
Epoxy Curing_____________________________________ 3
Types of Epoxy Resins____________________________ 4
Bisphenol A Epoxies______________________________ 4
Bisphenol F Epoxies______________________________ 5
Novolac Epoxies__________________________________ 6
Curing Agents____________________________________ 8
Evaluating the Various
Types of Epoxy Coating Systems_________________ 10
Alternative Polyaspartic Coating Systems________ 14
Use Applications for Epoxy Systems_______________15
Surface Preparation_____________________________ 18
Conclusion______________________________________ 20
Useful References_______________________________ 20
Epoxy Coatings 101: What Kind to Use and When
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EPOXY COATINGS 101:
WHAT KIND TO USE AND
WHEN
Epoxies are thermoset plastics typically made by the reaction of two
or more chemical compounds that develop a hard and chemically
resistant surface. The cured epoxy is used in a wide array of consumer
and industrial applications due to its material hardness, strong
adhesion, chemical resistance and other specialized properties.
Such cured epoxies make durable coatings and can be used for
a variety of purposes including strong adhesives, paints, primers
and coatings for metals and floors. For example, one of the most
economical approaches for the prevention of material degradation
or corrosion is to use an epoxy coating. Another application is for
high performance, heavy-duty protective flooring. For ambient
temperature applications, epoxy and polyaspartic coating systems
are preferred because of their protective properties and ease of
application on metallic and concrete surfaces. This whitepaper will
discuss the chemistry, properties, applications and examples of use
for these types of coatings.
Epoxy Coatings 101: What Kind to Use and When
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EPOXY CURING
Generally, epoxies are cured as one component (1k) or two
component (2k) systems. The 2k system consists of an epoxy
resin, which is often referred to as Part A, and the epoxy curing
agent or hardener, which is usually referred to as Part B. These
are mixed together prior to application and on curing develop a
highly crosslinked macromolecular structure. The applicator has
a specific amount of time to apply the coating before the system
gels or becomes hard. The 1k system will contain both the epoxy
and the hardener together in the same pot, but will be more
dependent on the evaporative properties in comparison to the 2k
system; therefore, the 1k system is not commonly used for coating
applications.
Figure 1. Epoxide chemical structure.
Epoxy Coatings 101: What Kind to Use and When
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TYPES OF EPOXY RESINS
The most common Part A components are bisphenol A, bisphenol
F or novolac resins.
BISPHENOL A EPOXIES
Bisphenol A epoxies are general purpose and are very cost effective.
This type of epoxy has excellent alkali resistance, good acid resistance
and reasonable solvent resistance.
Bisphenol A is a reaction product of phenol and acetone, which
is then reacted with epichlorohydrin via a condensation reaction
to form diglycidyl ether bisphenol A resin or DGEBA. The DGEBA
has a honey-like viscosity that is often used in solvent-free coatings
and flooring systems. By increasing the concentration of bisphenol
A in liquid DGEBA, a higher molecular weight formulation can be
produced that form semi-solid or solid resins. Such resins require a
solvent to reduce their viscosity to allow their use as maintenance
primers for steel or as corrosion resistant films. The higher molecular
weight formulation allows for longer branching when cured with
the hardener. With more reactive sites per DGEBA molecule, the
greater the three-dimensional crosslink density of the resultant
cured epoxy. The higher the crosslink density, the greater the
hardness and chemical resistance of the cured epoxy. Bisphenol
A epoxy resins are widely used for epoxy coatings for concrete and
steel.
One of the highest volume cycloaliphatic epoxies is hydrogenated
bisphenol A epoxy. It exhibits a lower resin viscosity and lower glass
Epoxy Coatings 101: What Kind to Use and When
5
transition temperature than DGEBA with the same number of repeat
units but also has superior moisture resistance, better UV-stability,
better color and gloss stability, higher impact resistance, improved
dimensional stability and higher thermal stability.
BISPHENOL F EPOXIES
Bisphenol F epoxies have a lower viscosity, excellent alkali resistance
and better acid and solvent resistance compared to Bisphenol A.
The difference between the two is that the bisphenol F is produced
from the reaction of phenol with formaldehyde, which results in a
phenolic chemical lacking the two methyl groups that are present
between the ring structure of bisphenol A resins. Bisphenol F is
then reacted with epichlorohydrin to form the diglycidyl ether
bisphenol F resin or DGEBF. Because of the missing two methyl
groups, the viscosity of DGEBF resins is about one-third of that
of the equivalent DGEBA resins. The lower viscosity results in the
requirement for fewer additives and diluents for ease of application.
With this chemistry there is a higher proportion of trifunctional
epoxy molecules, which can somewhat enhance the strength and
chemical resistance of the cured epoxy.
An advantage of the bisphenol F epoxy resins is they are less likely
to crystallize at low temperatures during curing. Heating the resin
to re-liquefy the crystals is feasible, but heating the resin pot at the
job site is non-trivial.
Epoxy Coatings 101: What Kind to Use and When
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NOVOLAC EPOXIES
Novolac epoxy resins are modifications of bisphenol F formed
by using excess phenol. This results in epoxy resins with a higher
molecular weight and thus higher viscosity. The higher molecular
weight produces a resin that has better chemical resistance and the
aromatic ring structure increases the heat resistance of the cured
epoxy. Novolac resins tend to be more brittle but the brittleness
can be reduced through formulation and curing agent selection.
Note that resin content is often modified by the formulator in order
to impart certain desirable properties such as chemical resistance.
In addition, the formulator can also alter the chemistry to produce
a required surface appearance or specific application properties.
Typical properties for these resins are shown in Table 1.
Table 1
Relative Performance Properties of Epoxy Resins
Typical Performance
Property
Bis A
Epoxy
Bis F
Epoxy
Novolac
Epoxy
Adhesion
H
H
H
UV protection
L
L
L
Abrasion resistance
H
H
H
VOCs
M
H
H
Crystallization
L
H
H
Moisture tolerance
H
H
H
Heat resistance
L
M
H
Chemical resistance
L
M
H
Epoxy Coatings 101: What Kind to Use and When
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Sulfuric acid
L
M
H
Acetone
L
M
H
Methanol
L
M
H
Sodium hydroxide
H
H
H
Organic acids
L
L
H
Performance: H – Highest, M – Medium, L – Lowest
(Source: J.D. Durig, “Comparisons of Epoxy Technology for
Protective Coatings and Linings in Wastewater Facilities”,
Proceedings of the Seminars, SSPC 99-14, p 31-37, 1999)
CURING AGENTS
There are many epoxy curing agents available, some of which are
polyamine based. These promote the crosslinking reaction and fall
into one of four categories:
1. Aliphatic and cycloaliphatic amines and polyamines
2. Amides and polyamides
3. Cycloaliphatic
4. Amine adducts
The type of curing agent determines the properties of the final
cured epoxy, including pot life, dry time, penetration, wetting ability
and hardness.
Aliphatic ethylene amines include aminoethyl piperazine,
diethylene triamine, ethylene diamine and triethylene tetramine.
Epoxy Coatings 101: What Kind to Use and When
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These curing agents have high reactivity and thus the curing is
fairly fast at ambient temperatures.
The amine-based curing agents usually produce more durable and
chemically resistant coatings than amide-based curing agents but
most have a tendency to blush in moist conditions. Blushing is a
reaction between the curing agent and the moisture in the air; this
produces a waxy surface layer on actively curing epoxy. Formulators
may modify these agents with other hardeners to obtain the
desired properties. For example, hexamethylene diamine and
trimethyl hexamethylene diamine are a class of aliphatic ethylene
polyamines that minimize blushing. Because of their structure they
have greater compatibility with the resin but produce less flexible
and higher hardness cured systems. Formulation modifications
can overcome some of these issues.
Polyetheramines result in good color retention, good flexibility
and reduced carbonation tendencies but react more slowly.
Metaxylylene diamine has good compatibility with epoxy resins,
and because of the aromatic backbone it has good heat resistance.
Because it also has unhindered primary amines in the structure, the
resin can cure at lower temperatures. However, because potentially
toxic chemicals from the curing agent can also be released, aliphatic
amines tend to be viewed less favorably.
Polyamides and amidoamines are more surface-tolerant and less
troubled by moisture than the aliphatic amines. In addition, this
class of curing agent has lower viscosity, improved adhesion, longer
pot life, less risk for carbonation and fewer health hazards. The
advantage is from the inclusion of a fatty acid into the backbone
of the molecule from the reaction of tall oil fatty acid and ethylene
amine. Typical applications include their use as primers or tie-coats
for steel and concrete.
Epoxy Coatings 101: What Kind to Use and When
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Cycloaliphatic curing agents generally provide better water/
moisture resistance, weatherability, low blush and water spotting,
heat resistance and better chemical resistance. The stretch of
the ring structure imparts better impact resistance, rigidity and
mechanical strength. Most widely used are isophorone diamine
and diaminocyclohexane. High performance epoxy coatings
employ a Part B curing agent that is a blend consisting partially
of cycloaliphatics. Bis-(p-aminocyclohexyl) methane curing agent
produces good low temperature cure properties with good heat
resistance and mechanical strength, which yields a tougher coating
and solvent resistance. Acid resistance is somewhat reduced
depending on the formulation.
Part B curing agents of amine adducts are produced when an amine
such as diethylene triamine is reacted with a small amount of the
epoxy resin where an active hydrogen of the residual amino groups
is formed. This produces a curing agent where there has already
been some initial curing. The pre-reacted amine adduct prior to
application is mixed with the polyamine curing agent to produce
the cured epoxy. The resulting epoxy is much like other epoxies,
but because of the higher molecular weight it has improved overall
physical properties including less volatility with little amine odor,
less toxicity, less exotherm output, better color stability and curing
at slightly cooler temperatures. Curing time may also be faster than
with epoxies using other types of curing agents.
EVALUATING THE VARIOUS TYPES OF EPOXY
COATING SYSTEMS
To obtain the desired optimum cured epoxy properties, the
thermoset resins and hardeners must be mixed. However, it is
Epoxy Coatings 101: What Kind to Use and When
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critical that a specific amount of hardener is used for a certain
weight of resin as specified by the formulator. For specialty epoxy
systems the formulator can vary the epoxy equivalent weight,
which is the weight of material that is considered to have one
reactive site in order to produce cured material with specific
properties.
Solvent-borne epoxy resins have an issue with the release of
volatile organic compounds (VOCs) during application and are no
longer as widely used. Waterborne epoxy systems were developed
to overcome this issue.
There are two basic coating systems, often referred to as Type I and
Type II. The Type I system primarily consists of liquid bisphenol A
and epoxy resins with an epoxy equivalent weight that is less than
250, while Type II is mostly composed of solid epoxy resin with a
higher molecular weight.
For Type I systems, the curing agent both crosslinks the epoxy
resins in the final form and also serves as the emulsifier for the
epoxy resin. Thus, immediately after mixing the emulsion particles
contain both the curing agent and the epoxy resin. There may also
be some amine in the aqueous phase. Waterborne Type I systems
are typically formulated to a zero volatile organic compound and
because of their good handling, flow and film formation properties
do not require a co-solvent. In addition, the low epoxide equivalent
weight of the epoxy resin has a high concentration and close
proximity of epoxide groups within the same dispersed particle
that leads to a rapid reaction within the particle. This can result
in a short working or pot life. After the water evaporates from
the system, the particles will coalesce and produce a relatively
uniform morphology form because of the high rates of diffusion.
Epoxy Coatings 101: What Kind to Use and When
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This results in a coating with good adhesion.
Originally Type II solid epoxy at about 50 to 55% solids content is
pre-dispersed in water and co-solvent with an emulsifier. Because
of the potential for poor flow and coalescence of solid epoxy
particles, about 5-10% glycol ether is added to the dispersions. To
react with the epoxy resin, curing agents are needed to migrate
from the water phase to the dispersed epoxy particles. As the water
evaporates a heterogeneous film forms as the coating coalesces.
Although the properties of the resulting coating are good, they
still produced some VOCs and have thus been primarily replaced
by the development of the 100% solids-based epoxy systems.
A 100% solids-based epoxy system was developed to eliminate
any VOC and water. Basically, it is simply resin that is mixed with
some hardener or reactive diluent. No water or co-solvents are
used. Thus, rather than drying by evaporation, it is cured. This
type of epoxy system creates the thickest coating, about 10 mils or
more, and results in the strongest coating in a single application.
They tend to be more abrasion, stain and chemical resistant and
have a high gloss finish. These epoxy systems provide excellent
durability, and depending on formulation and installation
technique, can protect concrete from chemical exposure, impact
and other abuse. The biggest issue is the short pot life for these
epoxy systems.
There are many benefits for the 100% solids-based epoxy
polymeric system. Because there is no solvent the coating
thickness remains almost identical before and after curing.
The lack of solvent also renders these systems almost odorless.
Since there is little shrinkage, a single coating can achieve
thicknesses of about 10 mils. Curing time and return to service
Epoxy Coatings 101: What Kind to Use and When
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is shorter because the curing is via an exothermic reaction.
Because crosslinking density is higher compared to waterborne
formulations, their mechanical properties are better. Table 2
compares generic waterborne to 100% solid epoxy systems.
Table 2
Comparison of Epoxy Systems
Attribute
Waterborne
100% Solids
Volatile organic compounds
Low to zero
Low to zero
Coating thickness per
application
Less
More
Requirement for multiple
applications
Yes
None
Typical single coating
thickness
3 mils
10 mils
Cost for 10 mil thickness
coating
Greater
Less
Cure time
Longer
Less
Pot life
Longer
Shorter
Industrial applications
Light
Heavy
Durability
Good
Longer
Chemical resistance
Good
Better
Abrasion resistance
Good
Better
UV stability
Poor
Poor
Epoxy Coatings 101: What Kind to Use and When
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ALTERNATIVE POLYASPARTIC COATING SYSTEMS
Polyaspartic systems are a hybrid material that is similar to
polyurethane and is based on an aliphatic polyisocyanate that is
reacted with an aliphatic diamine. This makes up a special class of
hindered secondary amines that have been specially designed for
certain properties for specific coating applications. The reactivity
of these amines is influenced by steric hinderance and the intramolecular hydrogen bonding. Modifications of the polyaspartic
ester resin and polyisocyanate allow the formulator to optimize the
pot life and dry time of the coating, and forgo the use of tin catalysis.
The elimination of the tin catalyst permits thicker film application
than is possible with traditional polyurethane coatings as well as
the microblistering from the release of carbon dioxide because of
the tin catalyzed reaction of isocyanate with water.
For these systems, atmospheric moisture vapor catalyzes the
polyaspartic curing reaction. Thus, the coating cures quickly but
maintains a workable pot life. Curing time is faster than the epoxy
resin systems and depending on the formulation can be applied
and cured at below freezing temperatures. The result is a hard,
durable surface with excellent abrasion, chemical resistance and
UV-stability, with the UV-stability being better than available from
epoxy systems.
These types of coatings have low or zero VOC. However, solvent
based polyaspartic systems release VOCs and require good
ventilation during installation.
Surface preparation is critical for proper coating adhesion.
Polyaspartic coatings, such as the Performance Industries Poly
200, can be used as a top coat over an epoxy coating, resulting
Epoxy Coatings 101: What Kind to Use and When
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in a complete flooring system with better UV-stability and more
comfortable walking because of its flexibility.
USE APPLICATIONS FOR EPOXY SYSTEMS
Epoxy systems applications include coatings, molded parts and
electronic packaging. For this whitepaper we will focus on the
flooring application and in particular coating concrete floors.
An epoxy coating on a concrete floor will provide a durable,
long lasting solution for a variety of commercial and industrial
applications, such as in manufacturing and industrial plants,
commercial and retail stores, hospitals, garages, warehouses, and
aircraft hangars to mention just a few. Such coatings can produce
a decorative, high gloss finish that is easy to clean, chemically
resistant and can eliminate potential safety hazards by improving
traction.
Figure 2. Epoxy systems provide an attractive and functional coating for
aircraft hangars and garages.
Both waterborne and 100% solid-based epoxy systems are widely
used for coating concrete flooring because of the broad range
of benefits they provide. These include long-term durability and
Epoxy Coatings 101: What Kind to Use and When
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life span, customizable color and appearance, moisture vapor
transmission mitigation, chemical resistance, slip resistance, ease
of cleaning, static control, thermal shock resistance and flexible
installation.
The solid-based epoxy system produces a thicker single application
heavy-duty coating that is hard, resilient and highly durable, while
the waterborne epoxy system may require additional coating
applications. The pot life is less for a 100% solid-based epoxy system,
but dries more rapidly and the floor will be back in operation more
quickly. Both systems require similar surface preparations.
Some formulators modify the resin and curing agent to enhance
properties such as abrasion or chemical resistance. A premium
100% solid-based epoxy system that has been specially modified
to optimize properties for flooring is Epoxy-Coat, a cycloaliphatic
product from Certified Performance Coatings. Certified
Performance Coatings is a world-class, high performance coating
systems formulator that specializes in industrial and commercial
floor coatings designed for high impact and abrasion and corrosion
resistance. Certified Performance Coatings formulations are unique
and have been developed based on customer input, testing and
applicator feedback and are available in an easy-to-use kit. All of
their resins must meet strict quality control standards.
Nearly one billion square feet of coated installations have used
products from Certified Performance Coatings. Epoxy-Coat is their
flagship product line for commercial and residential uses and can
be applied over concrete or asphalt, wood, and metal surfaces.
Pave-Patch is an epoxy product used to repair cement and asphalt
surfaces. Deck-Coat is perfect for outdoor use on cement, asphalt
and wood surfaces, and Counter-Coat is perfect for interior counter
Epoxy Coatings 101: What Kind to Use and When
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tops for bars, kitchens bathrooms. It is available in out rejection flake
colors from epoxy-coat and all of the metallic colors in Metallic Coat.
Metallic Coat is another epoxy-based product with primary uses
being interior floors from bars, restaurants and offices to kitchen
floors, garage floors and basements.
Because Epoxy-Coat can be applied in a single coat with a
thickness of 10 mils (five times the thickness of single application
waterborne epoxy coatings), the coating is long lasting. When
compared to a waterborne epoxy system, the coating can be ten
times more durable but at only 1.5 times the cost. It is self-leveling
with no odors. Aluminum oxide can be added to make a non-skid
surface. The product is available for both large-scale industrial and
commercial applications as well as for the do-it-yourselfer. It is the
same formulation as used by NASA.
Performance Industries provides a lifetime warranty for its EpoxyCoat product when used with a Poly 200 top coat. The Poly 200
is a UV stable, abrasion resistant, single component top coat
that outperforms polyurethane because it is polyaspartic based.
The Epoxy-Coat product data sheet provides the properties and
installation requirements. Performance Industries can provide
experienced, professional applicators for large commercial or
industrial projects, and tutorials for the do-it-yourselfer that wants
to obtain a professional coating for a home project.
Epoxy Coatings 101: What Kind to Use and When
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Figure 3. Layers of a coating system.
SURFACE PREPARATION
Surface preparation is critical for an acceptable application. The
concrete floor must be swept clean of debris, and any oils, grease
or sealant on the floor must be removed. With new concrete,
contaminants are released during curing and thus waiting about
28 days is usually recommended.
To minimize pinholes from air release from the concrete into the
coating, any temperature difference between the concrete and air
Epoxy Coatings 101: What Kind to Use and When
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should be minimal or the application should be performed in the
evening to allow for natural cooling. Many formulators recommend
application should be between 40-80°F (4-27°C).
For new and old concrete too much moisture being released can
affect the bond between the floor and the coating. Professional
instruments such as a non-invasive depth electronic moisture
meter can be used to check the conditions. For the do-it-yourselfer,
a reasonable trick is to completely tape down a plastic bag and
check on it after a day has passed. If there is any moisture present
when the plastic is peeled away then a moisture barrier coating will
be required before the epoxy coating can be applied.
Surface roughness can impact adhesion and should be examined
prior to installation. This is particularly critical for coating metal
surfaces. The do-it-yourselfer should follow the formulator’s
instructions such as provided by the Performance Industries EpoxyCoat video tutorial in order to obtain optimum results. Note that
most failures are not because of the coating but because of issues
associated with an inadequate or improper installation.
Preparation
Epoxy Coatings 101: What Kind to Use and When
Mixing
19
Application
After curing
Figure 4. Steps to installing an epoxy coating system.
To ensure proper surface preparation, one can also consider using an
installation company. Performance Floors and Performance Roads
both utilize Certified Performance Coatings for installation services.
Performance Roads handles larger projects, such as repairing
roads, bridge decks, curbs, highways and more. Performance
Floors specializes in epoxy coating installations on commercial and
residential floors.
CONCLUSION
Epoxy and polyaspartic systems have a wide range of commercial
applications. In this whitepaper we have focused on floor coating
applications, described the chemistry of the various commercially
available formulations and their strengths and weaknesses.
Formulators, such as Epoxy-Coat, modify the resins and curing
agents in order to optimize the properties of the resulting coating.
For this reason, there is no standard epoxy and not all epoxy systems
behave the same or have the same cured properties.
Epoxy Coatings 101: What Kind to Use and When
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USEFUL REFERENCES
1. K.B. Tator ed, ASM Handbook volume 5B: Protective Organic
Coatings (2015).
2. J.D. Durig, “Comparisons of Epoxy Technology for Protective
Coatings and Linings in Wastewater Facilities”, Proceedings of
the Seminars, SSPC 99-14, pp 31-37 (1999).
3. Three Bond Technical News, Curing Agents for Epoxy Resin
(1990).
4. Q.Xiang and F. Xiao, “Applications of epoxy materials in pavement
engineering”, Construction and Building Materials, 235 (2020).
5. M.J. Watkins, D.J. Weinmann and J.D. Elmore, Formulating HighPerformance Waterborne Epoxy Coatings (2006).
6. NACE No.6/SSPC-SP 13-2018, Surface Preparation of Concrete-2018
(2018).
7. J.R. Cavallo, “A Systematic Approach to Coating Failure Analysis”,
CoatingsPro, January 2021, pp 64-66.
8. Performance Epoxy Curing Agent Part B. Material Safety Data
Sheet.
9. Epoxy-Coat Floor Coating Kit. Product Data Sheet.
10. Epoxy-Coat Epoxy Flooring Installation Instructions.
Epoxy Coatings 101: What Kind to Use and When
21
169 N. Gratiot • Mt. Clemens, MI 48043
Office: 800-841-5580
Fax:
586-468-8440
Tech Support: support@epoxy-coat.com
CertifiedPerformanceCoatings.com
A family of professional high performance coating kits and installation
Epoxy-Coat
Metallic-Coat
Deck-Coat
Counter-Coat
Pave Patch
Do-It-Yourself Kits:
epoxy-coat.com
metallic-coat.com
counter-coat.com
deck-coat.com
PerformancePavePatch.com
Installation Services:
PerformanceFloor.com
PerformanceRoads.com
Expert Services Provided to:
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