What do you need to know about epoxy resins before using them for the first time?
Q. What do you need to know about epoxy resins before using them for the first time?
A. Epoxy is wonderful stuff, but before you set off on your first project you should be aware of safety procedures and safe working practices. All epoxy manufacturers produce safety data to be read, understood and followed. In short, avoid skin contact with uncured epoxy resins and hardeners, and always wear disposable gloves — medical examination gloves are my choice. Wear a long-sleeve shirt to protect forearms, or use an epoxy barrier cream if the weather is warm. When sanding epoxy use a suitable dust mask or respirator, and keep your work area clean.
When epoxy resin is mixed with a hardener in the correct ratio, a chemical reaction begins that makes the mixture turn hard. Both slow and fast hardeners are available. Which you use determines the amount of working time — or pot life — that you get. Epoxy can be mixed with filler powders to produce an
adhesive with gap-filling pro-parties. It is in this role that it has been used successfully in wood-composite construction.
Before using epoxy for the first time, I suggest making a small project — a toolbox for the boat — as a trial run. No fancy joints are necessary; simply cut the parts for the box, and glue them together with epoxy thickened with colloidal silica.
Basically, to make a joint proceed as follows:
In a plastic cup mix epoxy and hardener using a wooden mixing stick — a tongue depressor or ice cream stick with a rounded end is ideal. Coat the two parts to be joined with unthickened epoxy (this is called wetting out), but don’t bring them together yet. Thicken the remainder of the epoxy in the cup by stirring in silica powder until it has the consistency of ketchup. Spread a little of this onto each of the mating surfaces and bring them together. Do not overclamp. Pressure isn’t needed and may starve the glued area of adhesive. Where the adhesive mix has squeezed out of the inside corners use the rounded end of the mixing stick to form a fillet. Add more epoxy mix if insufficient glue squeezed out to form the fillet. Be as neat as possible to avoid sanding later. Without disturbing the fillet or the joint, scrape off any surplus or drips of adhesive. It is far easier to do this now than to think you can sand later — a mistake you’ll make only once.
When the fillet has partially cured, smooth over it with denatured alcohol. This could be any time between one to four hours after forming the joint, when the epoxy has taken on the consistency of hard toffee. This step isn’t essential, but it produces a smoother completed joint.
One of the best pieces of advice I can offer is to read up on the subject. “Gougeon Brothers on Boat Construction” (www.westsystem.com) contains a wealth of information from two people who have worked extensively with epoxy.