How to use Epoxy Resins

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Versatile Building and Repair Product
Epoxy resin, used in conjunction with its companion fillers, fabrics and tools, is one of the most versatile materials available for boat repair and construction. Epoxy-based resins owe their broad acceptance, by pros and amateurs alike, to the fact that they allow you to tackle such a wide variety of projects. Whether you want to repair gel coat cracks or a delaminating deck, install a bulkhead or even cold-mold a brand-new hull, you can create an epoxy mixture with the precise characteristics you need.

Key Applications
Epoxy uses fall into a few core categories:

  • Coating, where you apply one or more thin coats of epoxy to seal a surface or to prepare the surface for varnish or reinforcing layers like fiberglass or carbon fiber.
  • Bonding, where you use the epoxy as a glue, generally with some filler to allow it to fill gaps between the surfaces, or to attach hardware to a surface.
  • Laminating, where multiple layers of wood or other materials are laid up to create a thicker solid structure.
  • Fairing, where thickened resin is used to fill holes and depressions so that the surface can be sanded and smoothed.
Note that while many applications involve wood, epoxy resin can be used on fiberglass, carbon fiber, metals, etc.

How They Work
The heart of working with epoxy is the basic epoxy resin, combined with one of several hardeners. The clear amber resin cures to a high-strength plastic solid at room temperatures when mixed with specific proportions of the correct hardener. Hardeners are selected by the ambient temperature (which results in a reasonable “pot life”), or by a desired characteristic of the resulting mixture (like extra clarity for a clear finish in the case of WEST Systems 207 Hardener.)

Mixing the Epoxy
Epoxy resins are mixed with a specific proportion of hardener. We strongly recommend the use of calibrated pumps to deliver the proper mixture. When using these pumps, remember that the proper mixture is achieved when you mix one full pump of resin with one full pump of hardener (the different internal capacities of the pump barrels will measure just the right amount of liquid.)

To make it easier to buy, the right amount of resin and hardeners are packaged in group sizes. For each container size of resin, there is a corresponding container size of hardener like WEST System Group A or Group B.

Modifying the Epoxy Mixture
Because unmodified epoxy is both expensive and has low viscosity, you frequently add fillers or additives to create the right blend of properties for the job. Fillers are designed to thicken the epoxy mixture and are broadly grouped into two categories: High Density and Low Density.

High Density fillers are used to modify the structural properties of the epoxy by adding strength, bulk or both. Examples include WEST Systems #404 and #406. High density filler mixtures cure to a strong, hard-to-sand plastic useful in structural applications like bonding, filleting and laminating.

Low Density fillers cure to a light, easily-sanded material which is often used for cosmetic or surface applications such as shaping or fairing. Examples include WEST Systems #410 and #407.

Additives alter the physical properties when the epoxy mixture is used in coating applications. Barrier coat additive (#422) improves the effectiveness of the basic epoxy/hardener mixture at resisting moisture penetration. Adding graphite powder (#423) makes coated surfaces slick, which can be used on rudders, centerboards or centerboard trunks. Aluminum powder (#420) can be used to prevent UV deterioration.

Unlike additives and fillers, reinforcing materials are not mixed with the epoxy, but are often used in conjunction with the epoxy mixture to provide additional physical properties.

Safety
Like many other boat maintenance materials, epoxy resin products should be applied carefully. Please refer to the wide selection of books, manuals and videos on the uses of epoxy resins, for information on how to use them safely.

In Conclusion
We’ve found that using epoxy resin products has added a whole new dimension to our boat repair skills. We feel empowered to take on projects that we would have formerly delegated to a boat yard or boat maintenance worker. Resin has many additional applications at home when it comes to reinforcing furniture, patching surfaces, and other repairs.

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