Some people ask me about this subject. Here is something's to think about.
Thinning EpoxyThinning Epoxy Thinning epoxy means lowering its viscosity. Low viscosity epoxy flows better, is easier to roll or brush, and saturates fiberglass fabric quickly. There are two methods of temporarily thinning epoxy. One is to heat the mixture and the other is to add solvent to the mix. The goal of both methods is to reduce the epoxy's viscosity. Laboratory showed that adhesion to lower density wood species like Sitka spruce or Douglas fir, the weak link is the cross grain strength of the wood. It does not matter if the epoxy penetrates 1/4" into the wood or 5/1000". The strength of the wood, the amount of surface area and the adhesive ability of the glue determine the strength of a glue joint. Thinning epoxy with heat Heating the resin/ hardener components and then mixing them together results in a thinned epoxy mixture that, when cured, retains all the characteristics of epoxy cured at room temperature. The viscosity of epoxy is very sensitive to changes in temperature, and warming the components (resin and hardener) and/or the substrate substantially lowers its viscosity. Potential Problems Thinning epoxy with heat can create problems, warm epoxy cures much more quickly than you may be accustomed to. Have things organized before you mix the resin and hardener and move quickly. Use one of the slower hardeners to increase the working time. How warm is warm? You should be able to comfortably touch the substrate or the component containers when they are appropriately warmed, about 115°F maximum. Excessive heat will cause the epoxy to harden too fast, especially in thick applications. Thinning epoxy with solvent Adding solvent is a simple method of thinning epoxy, but unlike heat, the strength and moisture resistance of the cured epoxy are drastically affected. There are a large number of chemicals available to thin epoxy - acetone, lacquer thinner and denatured alcohol are the most commonly available and do a good job of reducing viscosity. For a variety of reasons, "fast evaporating" lacquer thinner appears to be more appropriate for thinning purposes than acetone or alcohol. · Adding 5% lacquer thinner makes about a 60% reduction in viscosity. · Adding 5% lacquer thinner to epoxy reduces the epoxy's compressive strength by 35%. · The addition of more than 5% solvent results in an excessively flexible cured material. · Solvent thinned epoxy cannot be used as structural adhesive. · Adding solvent extends the pot life and cure time and jeopardizes the reliability and predictability of cure. · Adding volatile solvent may cause shrinkage of the cured epoxy. · Applying thinned epoxy in large, confined areas is likely to trap some of the solvent. · Adding solvents alters the color of the cured epoxy. · The solvent used to thin epoxy may damage the substrate. · Solvents may be hazardous to your health and proper ventilation is mandatory. · Adding solvent to epoxy to enhance fiberglass wet-out will result in more "drain out" of the resin on a vertical surface. The fabric will wet-out quickly but it may become resin starved when too much epoxy runs out of the fabric. Does thinning epoxy make sense? In some situations, thinning is appropriate. In most circumstances using heat to thin epoxy is preferred to using solvents. As long as the epoxy does not overheat during cure, the full physical characteristics of the cured epoxy remain. Adding solvent is a quick, simple method of thinning epoxy, but the strength and moisture resistance of the cured epoxy are significantly reduced. So use this method on non-structural applications[such a epoxy microbloon fill] © Gougeon Brothers, Inc.
