This section explains the basic fundamentals of epoxy curing and the
proper dispensing, mixing, and adding fillers to assure that every batch of
epoxy cures to a useful high-strength solid.
Understanding cure stages
Mixing epoxy resin and curing, agent begins a chemical reaction that
transforms the combined liquid ingredients to a solid. The time it takes for this
transformation is the cure time. As it cures the epoxy passes from the liquid
state, through a gel state, before it reaches a solid state. Liquid-Open time
(also "working time" or "wet lay-up time") is the portion of the cure time, after
mixing, that the resin/curing agent mixture remains a liquid and is workable
and suitable for application. All assembly and clamping should take place
during the open time to assure a dependable bond.
The mixture passes into an initial cure phase (also called the green
it begins to gel, or "kick-off. The epoxy is no longer workable and will no
longer feel tacky. During this stage it progresses from a soft gel consistency to
the firmness of hard rubber, You will be able to dent it with your thumb nail.
Because the mixture is only partially cured, a new application of epoxy will
still chemically link with it, so the surface may still be bonded to or re-coated
without special preparation. However, this ability diminishes as the mixture
approaches final cure.
The epoxy mixture has cured to a solid state and can be dry sanded and
You should not be able to dent it with your thumbnail. At this point the epoxy
has reached about 90% of its ultimate strength, so clamps can be removed. It
will continue to cure over the next several days at room temperature. A new
application of epoxy will no longer chemically link to it, so the surface of the
epoxy must be sanded before re-coating to achieve a good mechanical,
Understanding and controlling cure time
Curing Agent speed
Each curing agent has an ideal temperature cure range. At any given
temperature, each resin/curing agent combination will go through the same
cure stages, but at different rates. Select the hardener that gives you adequate
working time for the job you are doing at the temperature and conditions you
are working under. Pot life is a term used to compare the usable life of different
hardeners. It is the amount of time 100 grams at 72 F remains a liquid. Because
pot life is a measure of the cure speed of a specific contained mass (volume) of
epoxy rather than a thin film, a hardener's pot life is much shorter than its open
The warmer the temperature, the faster the epoxy will cure. The
temperature is determined by the ambient temperature plus the exothermic heat
generated during cure. Ambient temperature is the temperature of the air or
material in contact with the epoxy. Air temperature is most often the ambient
temperature unless the epoxy is applied to a surface with a different
temperature. Generally, epoxy cures faster when it is warmer. Exothermic heat
is produced by the chemical reaction during cure. The amount of heat produced
depends on the thickness and surface area of mixed epoxy. In a thicker mass,
more heat is retained, causing a faster reaction and more heat. The mixing
container shape and mixed quantity have a great affect on this exothermic
reaction. A contained mass of curing epoxy (1 fl. oz. or more) in a plastic
mixing cup can quickly generate enough heat to melt the cup and burn your
skin. However, if the same quantity is-spread into a thin layer, exothermic heat
is dissipated, and the epoxy's cure time is determined by the ambient
temperature. The thinner the layer of curing epoxy, the less it is affected by
exothermic heat, and the slower it cures.
Controlling cure time
In warm conditions use a slower curing agent, or mix smaller batches
be used up quickly, or quickly pour the epoxy mixture into a container with
greater surface area (a flat pan, for example), thereby allowing exothermic heat
to dissipate and extending open time. The sooner the mixture is transferred or
applied (after thorough mixing), the more of the mixture's useful open time
will be available for coating, lay-up or assembly.
In cool conditions use a faster curing agent, or use supplemental heat to raise
the epoxy temperature above the curing agents minimum recommended
application temperature. Use a hot air gun, heat lamp or other heat source to
warm the resin and curing agent before mixing or after the epoxy is applied. At
room temperature, supplemental heat is useful when a quicker cure is desired.
CAUTION! Heating epoxy that has not gelled will lower its viscosity, allowing
the epoxy to run or sag more easily on vertical surfaces. In addition, heating
epoxy applied to a porous substrate (soft wood or low density core material)
may cause the substrate to "out-gas" and form bubbles in the epoxy coating. To
avoid out-gassing, wait until the epoxy coating has gelled before warming it.
Never heat mixed epoxy in a liquid state over 120F(49C).
Regardless of what steps are taken to control the cure time, thorough planning
of the application and assembly will allow you to make maximum use of
epoxy's open time and cure time.
Dispensing and mixing
Careful measuring of epoxy resin and curing agent and thorough
essential for a proper cure. Whether the resin/curing agent mixture is applied as
a coating or modified with fillers, observing the following procedures will
assure a controlled and thorough chemical transition to a high-strength epoxy
solid. Dispense the proper proportions of resin and curing agent into a clean
plastic, metal or wax-free paper container. Don't use glass or foam containers
because of the potential danger from exothermic heat build-up. DO NOT
attempt to alter the cure time by altering the ratio. An accurate ratio is
essential for a proper cure and full development of physical properties.
Dispensing with Mini pumps or Dual Syringes
Most problems related to curing of the epoxy can be traced to the wrong
of resin and hardener. To simplify metering, we recommend using calibrated
Anchor Bond Mini Pumps or Dual Syringes to dispense the resin and curing
agent. Mini Pumps are calibrated to deliver the proper working ratio of resin to
curing agent. Pump one full pump stroke of resin for each one full pump stroke
of curing agent. Depress each pump head fully and allow the head to come
completely back to the top before beginning the next stroke. Partial strokes will
give the wrong ratio. Read the pump instructions before using pumps. Before
you use the first mixture on a project, verify the proper ratio according to the
instructions that come with the pumps.
First Time Users
If this is the first time you have used Anchor Bond epoxy, begin with
test batch to get the feel for the mixing and curing process, before applying the
mixture to your project. This will demonstrate the hardener's open time for the
temperature you are working in and assure you that the resin/curing agent ratio
is metered properly. Mix small batches until you are confident of the mixture's
Stir the two ingredients together thoroughly. To assure thorough mixing,
the sides and bottom of the cup as you mix. Use the flat end of the mixing stick
to reach the inside corner of the cup. If you are going to be using the mixture
for coating, quickly pour it into a wide dish or pan to extend the open time.
Warning! Curing epoxy generates heat. Do not fill or cast layers of epoxy
thicker than 1/4", thinner if enclosed by foam or other insulated material. One
inch of mixed epoxy in a plastic mixing cup will generate enough heat to melt
the cup if left to stand for its full pot life. For this reason do not use foam or
glass mixing containers. if a pot of mixed epoxy begins to exotherm (heat up),
quickly move, it outdoors. Avoid breathing the fumes. Do not dispose of the
mixture until the reaction is complete and has cooled, as it might cause a fire.
After selecting an appropriate filler for your job, use it to modify
mixture to the desired consistency. The thickness of a mixture required for a
particular job is controlled by the amount of filler added. There is no strict
formula or measuring involved-use your eye to judge what consistency will
Always add fillers in a two-step process:
1. Mix the desired quantity of resin and curing agent thoroughly
fillers. Begin with a small batch to allow room for the filler.
2. Blend in small amounts of the appropriate filler until the
consistency is reached.
3. For thick mixtures, don't fill the mixing cup more than 1/3
full of epoxy
before adding filler.
Anchor Balloons are intended as a fairing and cosmetic filler.
They sand and
shape very easily. For fairing add as many Anchor Balloons as you can blend
in smoothly for easy sanding, usually the thicker the better.
Anchor Fibers are intended for use in high strength reinforcing
where fiberglass cloth is inappropriate or impractical to use.
Anchor Thickening is a fumed silica, intended for use in adjusting the
viscosity (thickness). It produces a stronger finished product than Anchor
Balloons, but is also much harder to sand. Be sure all of the fillers are
thoroughly blended before the mixture is applied. For maximum strength, add
only enough filler to completely bridge gaps between surfaces without sagging
or running out of the joint or gap. A small amount should squeeze out of joints
when clamped. All Anchor Bond fillers can be combined with each other to
suit specific applications and construction techniques.
The following basic techniques are common to most repair and building
projects, regardless of the type of structure or material you are working with.
Whether you are bonding, fairing or applying fabrics, the success of
application depends not only on the strength of the epoxy, but also on how well
the epoxy, adheres to the surface to which it is being applied. Unless you are
bonding to partially cured epoxy, the strength of the bond relies on the epoxy's
ability to mechanically "key" into the surface. That is why the following three
steps of surface preparation are a critical part of any secondary bonding
operation. For good adhesion, bonding surfaces should be:
Bonding surfaces must be free of any contaminants such as grease, oil,
mold release. Clean contaminated surfaces with lacquer thinner, alcohol,
acetone, MEK or brake cleaner. Be sure to read, understand and follow the
precautions on the container. Wipe the surface with paper towels before the
solvent dries. Clean surfaces before sanding to avoid sanding the contaminant
into the surface.
All bonding surfaces must be as dry as possible for good adhesion. If
necessary, accelerate drying by warning the bonding surface with hot air guns,
hair dryers or heat lamps. Use fans to move the air in confined or enclosed
Sand smooth non-porous surfaces thoroughly. 80-grit aluminum oxide paper
will provide a good texture for the epoxy to "key" into. Be sure the surface to
be bonded is solid. Remove any flaking, chalking, blistering, or old coating
before sanding. Remove all dust after sanding, by using a air gun, or tack cloth.
Epoxy surfaces that have not fully cured may be bonded to or coated with
epoxy, without washing or sanding. Before applying coatings other than epoxy,
allow epoxy surfaces to cure fully.
Wipe with acetone 15 minutes before coating. Solvent dries the oil at
surface and allows epoxy to penetrate. Be sure solvent has evaporated before
No special preparation needed. If surface is burnished, sand with 80-grit
to open pores.
Remove contamination, sand or grind to bright metal, coat with epoxy.
coat or bond after first coat gels, if desired.
Clean with a silicone and wax remover. Sand with 80-grit paper to a dull finish.
Adhesion varies. If a plastic is impervious to solvents such as acetone,
generally will not bond to it. Plastics such as: polyethylene, polypropylene,
nylon, Teflon, Plexiglas and polycarbonate fall into this category.
Hard, rigid plastics
Plastics such as PVC, ABS and polystyrene provide better adhesion with
surface preparation and adequate bonding area. After sanding, flame oxidizing
(by quickly passing propane torch over the surface without melting the plastic)
can improve bonding in some plastics. Its a good idea to conduct an adhesion
test on a plastic that you are uncertain about.
This section refers to two types of bonding. Two-step bonding is the
method for most situations because it promotes maximum epoxy penetration
into the bonding surface and prevents resin-starved joints. Single-step bonding
can be used when joints have minimal loads and excess absorption into porous
surfaces is not a problem. Before mixing epoxy, check all parts to be bonded
for proper fit and surface preparation. Gather all the clamps and tools necessary
for the operation, and cover any areas that need protection from spills.
1. Wet-out bonding surfaces by applying a straight resin/curing
(without fillers) to the surfaces to be joined. Wet-out small or tight areas
with a disposable brush. Wet-out larger areas with a foam roller or by
spreading the resin/curing agent mixture evenly over the surface with a
plastic squeegee. You may proceed with step two immediately or any time
before the wet-out coat reaches the final cure stage.
2. Apply thickened epoxy to one bonding surface. Modify the resin/curing
agent mixture by stirring in the appropriate filler until it becomes thick
enough to bridge any gaps between the mating surfaces and to prevent
"resin-starved" joints. Apply enough of the mixture to one of the surfaces so
that a small amount will squeeze out when the surfaces are joined together
with a force equivalent to, a firm hand grip. Thickened epoxy can be applied
immediately over the wet-out surface or, any time before the wet-out reaches
its final cure. For most small bonding operations, add the filler to the
resin/curing agent mixture remaining in the batch that was used for the wet-
out. Mix enough resin/curing agent for both steps. Add the filler quickly
after the surface is wet out and allow for a shorter working, life of the
3. Clamp components. Attach clamps as necessary to hold the components
place. Use just enough clamping pressure to squeeze a small amount Of the
epoxy mixture from the joint, indicating that the epoxy is making good
contact with both mating surfaces. Avoid using too much clamping
pressure, which can squeeze all of the epoxy mixture out of the joint.
4. Remove or shape excess adhesive that squeezes out of the joint as
the joint is secured with clamps. A wooden mixing stick with one end
sanded to a chisel edge is an ideal tool for removing the excess.
In single-step bonding, apply the thickened epoxy directly to the component
without first wetting out with resin/curing agent. We recommend that you
thicken the epoxy no more than is necessary to bridge gaps in the joint (the
thinner the mixture, the more it can penetrate the surface) and that you do not
use this method for highly-loaded joints or for bonding end-grain or other
The term "laminating" refers to the process of bonding numbers
thin sheets, like plywood, veneers, fabrics or core material to create a
composite. A composite may be any number of layers of the same material or
combinations of different materials. Methods of epoxy application and
clamping will differ depending on what you are laminating.
Because of large surface areas and limitations of wet lay-up time, roller
application is the most common method for applying epoxy. A faster method
for large surfaces is to simply pour the resin/curing agent mixture onto the
middle of the panel and spread the mixture evenly over the surface with a
plastic spreader. An even distribution of weights will work when you are
laminating a solid material to a base that will not hold staples, such as a foam
or honeycomb core material. Vacuum bagging is also a method for laminating
a wide range of materials. Through the use of a vacuum pump and plastic
sheeting, the atmosphere is used to apply even clamping pressure over all areas
of a panel regardless of the size, shape or number of layers.
Any method of clamping is suitable as long as the parts to be joined
are held so
that movement will not occur. Methods of clamping include spring clamps,
"C" clamps, heavy rubber bands, nylon-reinforced packaging tape, applying
weights, and vacuum bagging. When placing clamps near epoxy-covered areas,
use polyethylene sheeting or wax paper under the clamps so they don't
inadvertently bond to the surface. In some cases the thickened epoxy or gravity
will hold parts in position without clamps.
Bonding with fillets
A fillet is a cove-shaped application of thickened epoxy that bridges
corner joint. It is excellent for bonding parts because it increases the surface
area of the bond and serves as a structural brace. All joints that will be covered
with fiberglass cloth will require a fillet to support the cloth at the inside corner
of the joint. The procedure for bonding with fillets is the same as normal
bonding except that instead of removing the squeezed-out thickened epoxy
after the components are clamped in position, you shape it into a fillet. For
larger fillets, add thickened mixture to the joint as soon as the bonding
operation is complete, before the bonding mixture is fully cured, or any time
after the final cure and sanding of exposed epoxy in the fillet area.
1.Bond parts as described above.
2. Shape and smooth the squeezed-out thick epoxy into a fillet by drawing
rounded filleting tool (mixing stick) along the joint, dragging excess
material ahead of the tool and leaving a smooth cove-shaped fillet bordered
on each side by a clean margin. Some excess filleting material will remain
outside of the margin. Use the excess material to re-fill any voids. Smooth
the fillet until you are satisfied with its appearance. A mixing stick will
leave a fillet with about a 3/8" radius.
3. Clean up the remaining excess material outside of the margin by using
sharpened mixing stick or a putty knife. Fiberglass cloth or tape may be
applied over the fillet area before the fillet has cured (or after the fillet is
cured and sanded).
4. Sand smooth with 80-grit sandpaper after the fillet has fully cured.
surface clean of any dust.
1. Fairing refers to the filling and shaping of low areas so they blend
surrounding surfaces and appear "fair" to the eye and touch. After major
structural assembly has been completed, final fairing can be easily
accomplished with Anchor Bond epoxy and low-density fillers.
2. Prepare the surface as you would for bonding. Sand smooth any bumps
ridges on the surface and remove all dust from the area to be faired.
3. Wet out porous surfaces with un-thickened epoxy.
4. Mix resin/curing agent and Anchor Balloons to a peanut butter consistency.
5. Trowel on the thickened epoxy mixture with a plastic squeegee, working
into all voids and depressions. Smooth the mixture to the desired shape,
leaving the mixture slightly higher than the surrounding area. Remove any
excess thickened epoxy before it cures.
6. Allow the final thickened epoxy application to cure thoroughly.
7. Sand the fairing material to blend with the surrounding contour.
50-grit sandpaper if you have a lot of fairing material to remove. Use 80-
grit paper on the appropriate sanding block when you are close to the final
contour. CAUTION! Don't forget your dust mask. Remove the sanding dust
and fill any remaining voids following the same procedure.
Applying woven cloth & tape
Fiberglass cloth is usually applied after fairing and shaping
are completed, and
before the final coating operation. it is also applied in multiple layers
(laminated) and in combination with other materials to build composite parts.
Fiberglass cloth may be applied to surfaces by either of two methods. The
"dry" method refers to applying the cloth over a dry surface. The "wet" method
refers to applying the cloth to an epoxy-coated surface often after the wet-out
coat becomes tacky, which helps it cling to vertical or overhead surfaces. Since
this method makes it more difficult to position the cloth, the dry method is the
preferred method especially with thinner cloth.
1. Prepare the surface as you would for bonding.
2. Position the cloth over the surface and cut it several inches
larger on all
sides. If the surface area you are covering is larger than the cloth size, allow
multiple pieces to overlap. On sloped or vertical surfaces, hold the cloth in
place with masking or duct tape, or with CA.
3. Mix a small quantity of epoxy.
4. Pour a small pool of resin/curing agent near the center of the cloth.
5. Spread the epoxy over the cloth surface with a plastic spreader,
epoxy gently from the pool into the dry areas. Use a foam roller or brush to
wet out fabric on vertical surfaces. Properly wet out fabric is transparent.
White areas indicate dry fabric. If you are applying the cloth over a porous
surface, be sure to leave enough epoxy to be absorbed by both the cloth and
the surface below it. Try to limit the amount of squeegeeing you do. The
more you "work" the wet surface, the more minute air bubbles are placed in
suspension in the epoxy. This is especially important if you plan to use a
clear finish (see below). You may use a roller or brush to apply epoxy to
horizontal as well as vertical surfaces.
6. Smooth wrinkles and position the cloth as you work your way
to the edges.
Check for dry areas (especially over porous surfaces) and re-wet them as
necessary before proceeding to the next step. If you have to cut a pleat or
notch in the cloth to lay it flat on a compound curve or corner, make the cut
with a pair of sharp scissors and overlap the edges.
7. Note: For clear wood finishes, an alternative wet out
method is to lay the
epoxy onto the fabric with a short-bristled brush. Dip the brush in the epoxy
and lay the epoxy on the surface in a light even stroke. Don't force the
epoxy into the cloth, which may trap air in the fabric and show through the
clear finish. Apply enough epoxy to saturate the fabric and the wood below.
After several minutes, lay on additional epoxy to dry (white) areas.
8. Squeegee away excess epoxy before the first batch begins to
gel. Drag the
squeegee over the fabric, using even-pressured, overlapping strokes. Use
enough pressure to remove excess epoxy that would allow the cloth to float
off the surface, but not enough pressure to create dry spots. Excess epoxy
appears as a shiny area, while a properly wet-out surface appears evenly
transparent, with a smooth, cloth texture. Later coats of epoxy will fill the
weave of the cloth.
Trim the excess and overlapped cloth after the epoxy has reached its initial
cure. The cloth will cut easily with a sharp utility knife. Coat the surface to
fill the weave before the wet-out reaches its final cure stage. Follow the
procedures for final coating below. It could take two or three coats to
completely fill the weave of the cloth and to allow for a final sanding that
will not affect the cloth.
An alternative is to apply the fabric or tape to a surface coated with
As mentioned, this is not the preferred method, especially with large pieces of
cloth, because of the difficulty removing wrinkles or adjusting the position of
the cloth as it is being wet out. However, you may come across situations when
this method may be useful or necessary,
1. Prepare the surface for bonding.
2. Pre-fit and trim the cloth to size. Roll the cloth neatly so that it may be conveniently rolled back into position later.
3. Roll a heavy coat of epoxy on the surface
4. Unroll the glass cloth over the
wet epoxy and position it. Surface tension will hold most cloth in position.
If you are applying the cloth vertically or overhead,
you may: want to wait until the epoxy becomes tacky. Work out wrinkles by lifting the edge of the cloth and smoothing from the center with your gloved hand
or a squeegee.
5. Apply a second coat of epoxy with a foam roller, or brush. Apply enough epoxy to thoroughly wet out the cloth.
6. Follow steps 6, 7, and 8 under the dry method to finish the procedure.
7. Any remaining irregularities or transitions between cloth and substrate can be faired by using an epoxy/filler fairing compound.
8. Note: A third alternative, a
variation of both methods, is to apply the fabric after a wet out coat
has reached an initial cure. Follow the first three steps of the
Wet Method, but wait until the epoxy cures tacky to the touch before positioning the fabric and continuing with Step 3 of the Dry Method. Apply the fabric
before the first coat reaches its final cure phase.
Final surface preparation
Proper finishing techniques will not only add beauty to your efforts,
also protect your work from ultraviolet light which will- break down the epoxy
over time. The most common methods of finishing are painting or film coating.
These coating systems protect the epoxy from ultraviolet light and require
proper preparation of the surface before application. Preparation of the final
finish is just as important as it is for re-coating with epoxy. The surface must
first be clean, dry and sanded.
Allow the final epoxy coat to cure thoroughly.
1. Sand to a smooth finish. If there are runs or sags,
begin sanding with 80 grit
paper to remove the highest areas. Sand until the surface feels and looks
fair. Complete sanding with the appropriate grit for the type of coating to be
applied. Paint adhesion relies on the mechanical grip of the paint keying
into the sanding scratches in the epoxy's surface. If a high-build or filling
primer is to be applied, 100 grit is usually sufficient. 120-180 grit may be
inadequate for primers and high-solids coatings. Finishing with 220-400 grit
paper will result in a high-gloss finish for most paints. Grits finer than this
may not provide enough tooth for good adhesion. Wet sanding is preferred
by many people because it reduces sanding dust.
2. After you are satisfied with the texture and fairness
of the surface, rinse the
surface with fresh water. Rinse water should sheet evenly without beading
or fish-eyeing. If rinse water beads up (a sign of contamination), wipe the
area with solvent and dry with a paper towel, then wet sand again until
beading is eliminated. Proceed with your final coating after the surface has
dried thoroughly. To reduce the possibility of contamination, it is a good
idea to begin coating within 24 hours of the final sanding. Follow all of the
instructions from the coating system's manufacturer. It may be a good idea
to make a test panel to evaluate the degree of surface preparation required
and the compatibility of the finish system.
ANCHOR SEAL, INC.
16 Riverside Avenue
Danvers, MA 01323-3281
Phone (800) 669-5217
Fax (978) 774-0638
Email: [email protected]