Epoxy is a wonderful modern material used as glue and as a building material in kayaks. It is essentially liquid plastic resin. This resin is typically combined with fiberglass to make a composite material FRP.
The chemical name for epoxy resin is the diglycidol ether of bisphenyl A (DGEBA). In general, epoxy comes as a two part system. The two parts are the resin and a hardener. Different companies have different hardeners and the mixtures are in different ratios. Normally there is an equal amount or less of the hardener as compared with the resin. 1:1, 1:2, 1:3, 1:5 mixtures are common.
When mixing epoxy, protective equipment is necessary. Almost all hardeners are skin sensitizers – i.e. they act like the oil on poison ivy leaves. You may not be allergic to the chemical in the beginning, but if you keep exposing your skin, you will become sensitized and even small amounts of exposure will become a problem in the future. ALWAYS wear protective gloves and do not allow either the resin or the hardener to touch your skin. If it does, wipe off with a dry cloth immediately. Avoid use of solvents like acetone which will work the chemical into your skin. If the epoxy is still uncured, vinegar will help remove it from skin.
When working in an enclosed area like the inside of a kayak, use of a respirator (not a painter’s mask) is important. Good ventilation of the work area is a must.
The chemical reaction which begins when the two chemicals are combined is what ends up causing the two liquids to become a solid piece of epoxy plastic. A few details about the chemical reaction are useful:
- The reaction is faster when the materials are warmer
- The reaction creates heat (exothermic)
- The reaction will not work well if the mixing ratio is wrong
- The reaction will not work for the part of the mixture where the ratio is wrong.
Several practical hints on the application of epoxy follow from these facts:
- Choosing a day when the temperature is in the range recommended for the hardener is important.
- In addition, many state that epoxy should usually be applied when the day is cooling, so that any bubbles forming will shrink instead of expanding
- Mixing small batches and quickly applying them into a thin coat allows the heat of reaction to be lost into the air instead of cooking off in the mixing cup. Use a wide mouth, shallow cup rather than a small mouth, deep cup.
- Careful measurement is important. Epoxy measurement methods should be carefully chosen and applied.
- When mixing epoxy, thorough mixing for a full minute, paying close attention to the bottom and sides is very important.
- An additional pouring of the mixed epoxy into a different container before applying comes highly recommended by many
Most people make a mistake sometime with epoxy. If a batch does not harden, it must be removed with a scraper and then with acetone, down to a hard surface. It takes work, but is possible. Since acetone is being used, be especially careful to use vinyl gloves (see Protective gloves) (not latex which is porous to acetone) and lots of ventilation. Acetone vapors are very flamable.
Manufacturer’s recommendations for applying subseqent coats are important to follow. Fresh liquid epoxy will stick very well to partially cured epoxy but does not stick well to cured epoxy. All epoxy formulations are prone to some amine blush, though the best produce little. Amine blush must be removed before recoating and can be removed by washing with warm water or by wet sanding. Almost all epoxy coatings become cured when they have been in the hardened state for more than 24 hours. A new layer of epoxy applied to cured epoxy will not bond well to the existing layer. This can be avoided by sanding the hardened epoxy. Sanding provides more surface for the new epoxy to stick to.
Avoid 5 minute epoxies from hardware stores – they tend to be cheap. If you need a small batch of epoxy, some of the manufacturers below sell mini-repair packs that contain small envelopes of epoxy – sort of like the ketchup or mustard plastic packs offered in fast-food joints.
For repairs, you can also get epoxy putties. Aquamend is one brand and it will cure under water. The epoxy is in the form of two layers of paste that must be kneeded to mix them together. One of the components is coloured, while the other is white or off-white. When mixed correctly, the colour disappears and the mix is completely white or off-white. Wear gloves when kneeding the putty and applying it. Once applied, it can be shaped with a spatula, spreader or mixing stick. Once cured, it can be sanded to finish the surface. A good addition to an emergency repair kit.
