This User Manual is the primary guide to the handling and
basic techniques of epoxy use. It describes how to dispense, mix and modify WEST SYSTEM
epoxy for the basic coating, filling and bonding techniques used in most repair and
These procedures are described in detail in WEST SYSTEM instructional
publications and videos.
For complete descriptions of all WEST SYSTEM products, including selection and coverage
guides, go to the Product Guide.
- To help you identify and prevent potential problems
associated with using epoxy, go to the Problem Solver.
- For complete information on the hazards associated with
epoxy and the precautions you can take to avoid them, go to Health & Safety.
- To see how these techniques have been put to use in a wide
range of repair and construction applications go to the Projects
Epoxy's cure stages
Mixing epoxy resin and hardener 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 (Figure 1).
| As it cures, mixed epoxy passes from a liquid state, through a gel state, to a solid state.
1. Liquid-Open time Open time (also working time or wet
lay-up time) is the portion of the cure time, after mixing, that the resin/hardener
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.
2. Gel-Initial cure The mixture passes into an initial cure
phase (also called the green stage) when it begins to gel or "kick-off." The
epoxy is no longer workable and will no longer feel tacky. During this do not disturb
stage it progresses from a soft gel consistency to the firmness of hard rubber. You will
be able to dent it with your thumbnail.
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 recoated without special preparation. However, this ability diminishes as the
mixture approaches final cure.
3. Solid-Final cure The epoxy mixture has cured to a solid state and can be dry sanded and
shaped. 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 properly prepared and sanded before
recoating to achieve a good mechanical, secondary bond. See Surface Preparation
Understanding cure time
Open time and cure time govern much of the activity of
building and repairing with epoxy. Open time dictates the time available for mixing,
application, smoothing, shaping, assembly and clamping. Cure time dictates how long you
must wait before removing clamps, or before you can sand or go on to the next step in the
project. Two factors determine an epoxy mixture's open time and overall cure time-hardener
cure speed and epoxy temperature.
Each hardener has an ideal temperature cure range. At any
given temperature, each resin/hardener 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. The product
guide and container labels describe hardener pot lives and cure times.
Pot life is a term used to compare the cure speeds of
different hardeners. It is the amount of time a specific mass of mixed resin and hardener
remains a liquid at a specific temperature. (A 100g-mass mixture in a standard container,
at 72°F). 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
The warmer the temperature of curing epoxy, the faster it
cures (Figure 1). The temperature of curing epoxy is determined by the ambient temperature
plus the exothermic heat generated by its 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 the air temperature is warmer.
Exothermic heat is produced by the chemical
reaction that cures epoxy. The amount of heat produced depends on the thickness or exposed
surface area of mixed epoxy. In a thicker mass, more heat is retained, causing a faster
reaction and more heat. The mixing container's shape and the mixed quantity have a great
affect on this exothermic reaction. A contained mass of curing epoxy (8 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
hardener, if possible. Mix smaller batches that can be used up quickly, or pour the epoxy
mixture into a container with greater surface area (a roller 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
hardener, or use supplemental heat to raise the epoxy temperature above the hardener's
minimum recommended application temperature. Use a hot air gun, heat lamp or other heat
source to warm the resin and hardener before mixing or after the epoxy is applied. At room
temperature, supplemental heat is useful when a quicker cure is desired.
For detailed information on working with epoxy
at low temperatures, refer to 002-915 Cold
Temperature Bonding and Coating with Epoxy.
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 (softwood 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 120°F (49°C).
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.
Careful measuring of epoxy resin and hardener and thorough
mixing are essential for a proper cure. Whether the resin/hardener mixture is applied as a
coating or modified with fillers or additives, 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 hardener into a clean
plastic, metal or wax-free paper container (Figure 2). Don't use glass or foam containers
because of the potential danger from exothermic heat build-up.
DO NOT attempt to adjust the epoxy cure time by altering
the mix ratio. An accurate ratio is essential for a proper cure and full development of
- Dispensing with Mini pumps - Most problems
related to curing of the epoxy can be traced to the wrong ratio of resin and hardener. To
simplify metering, we recommend using calibrated WEST SYSTEM Mini Pumps to dispense the
resin and hardener. Mini Pumps are calibrated to deliver the proper working ratio of resin
Pump one full pump stroke of resin for each one full pump stroke of hardener. 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. Re-check the ratio anytime you experience problems
- Dispensing without Mini Pumps
(Weight/volume measure) - To measure 105 Resin and 205 or 206 Hardener by weight or
volume, combine five parts resin with one part hardener. To measure 105 Resin and 207 or
209 Hardener by volume, combine three parts resin with one part hardener (by weight, 3.5
parts resin-1 part hardener).
First time users
If this is the first time you have used WEST SYSTEM epoxy,
begin with a small 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/hardener ratio is metered
properly. Mix small batches until you are confident of the mixture's handling
Stir the two ingredients together thoroughly-at
least 1 minute-longer in cooler temperatures (Figure 3). To assure thorough mixing, scrape
the sides and bottom of the pot as you mix. Use the flat end of the mixing stick to reach
the inside corner of the pot. If you are using a power mixer, occasionally scrape the
sides and corners of the mixing pot while mixing.
If you are going to be using the mixture for coating,
quickly pour it into a roller pan to extend the open time.
WARNING! Curing epoxy generates heat. When contained, a large mass of
curing epoxy has a very short pot life, and can generate enough heat to melt plastic and
foam, burn your skin and ignite combustible materials. 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. Do not fill or cast layers of epoxy thicker than
1/2"-thinner if enclosed by foam or other insulating material. Do not pour into
Throughout this and other WEST SYSTEM manuals, we refer to epoxy,
neat epoxy or resin/hardener mixture, meaning mixed resin and hardener without
fillers added; and thickened mixture or thickened epoxy, meaning mixed resin and
hardener with fillers added. Fillers are used to thicken epoxy for
specific applications such as bonding or fairing.
After selecting an appropriate filler for your job (see Filler Selection Guide), use it
to thicken the epoxy 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 work
best. Figure 5 gives you a general guide to the differences between neat (unthickened)
epoxy and the three consistencies referred to in this manual.
Always add fillers in a two-step process:
1. Mix the desired quantity of resin and hardener
thoroughly before adding fillers. Begin with a small batch-allow room for the filler.
2. Blend in small handfuls or scoops of the appropriate filler until the desired
consistency is reached (Figure 4).
For maximum strength, add only enough filler to completely
bridge gaps between surface without sagging or running out of the joint or gap. A small
amount should squeeze out of joints when clamped. For thick mixtures, don't fill the
mixing cup more than 1/3 full of epoxy before adding filler. When making fairing
compounds, stir in as much 407 or 410 as you can blend in smoothly-for easy sanding, the
thicker the better. Be sure all of the filler is thoroughly blended before the mixture is
applied. Spread the mixture into a thinner layer, either around the inside of the mixing
cup or onto a flat non-porous surface or palette, to extend its working life.
|Epoxy can be
thickened to the ideal consistency needed for a particular job. The procedures in this
manual refer to four common consistencies: syrup, catsup, mayonnaise and peanut butter.
||Drips off vertical surfaces
||Coating; wetting-out before bonding; applying fiberglass, graphite and other
||Sags down vertical surfaces
||Laminating/bonding flat panels with large surface areas, injecting with a syringe
||Clings to vertical surfaces; peaks fall over
||General bonding, filleting, hardware bonding
|| Clings to vertical surfaces; peaks stand up
||Gap filling, filleting, fairing, bonding uneven surfaces