West System User Manual

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 construction procedures.

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.

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

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 open time.

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.

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.

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.

Dispensing

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 physical properties.

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 characteristics.

Mixing

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 confined spaces.

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.

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.

	SYRUP
	CONSISTENCY:	Unthickened mixture
	CHARACTERISTICS:	Drips off vertical surfaces
	USES:	Coating; wetting-out before bonding; applying fiberglass, graphite and other fabrics
	CATSUP
	CONSISTENCY:	Slightly thickened
	CHARACTERISTICS:	Sags down vertical surfaces
	USES:	Laminating/bonding flat panels with large surface areas, injecting with a syringe
	MAYONNAISE
	CONSISTENCY:	Moderately thickened
	CHARACTERISTICS:	Clings to vertical surfaces; peaks fall over
	USES:	General bonding, filleting, hardware bonding
	PEANUT BUTTER
	CONSISTENCY:	Maximum thickness
	CHARACTERISTICS:	Clings to vertical surfaces; peaks stand up
	USES:	Gap filling, filleting, fairing, bonding uneven surfaces