There are two primary ways to thin two-part epoxy. The first involves simply heating it, which improves its flow. The other is to add a solvent, and if you do this there are several options. A question to ask prior to thinning with a solvent is if you really need to. Often an epoxy, when used as a coating, will penetrate wood or concrete sufficiently without any dilution, but people often have the impression that reduced viscosity is needed for the best results. The other potential problem is losing the benefits you want from epoxy for in the first place.
Thinning Two-Part Epoxy
To thin the epoxy by heating, use a hairdryer. You can also put tubes of epoxy in the microwave. Ten seconds should be enough; take the tops off first so they don't overflow.
If you choose to thin the two-part epoxy with a solvent, think about whether it is necessary first. Often, an epoxy is easier to apply than you might anticipate, so test it prior to thinning. Also, even though it might not seem that you are getting the penetration into the surface that you want, it is likely that the product is working fine and might not work if it is thinned. For certain, the epoxy will be weakened if thinned, whether you are using a special coating or glue. Strength and impermeability are the desired qualities in two-part epoxy, and these will be degraded since the solids in the resulting mixture will be sparser.
To thin the epoxy, once the components have been mixed, usually either lacquer thinner or acetone are recommended, and sometimes denatured alcohol can be used. Check the labeling to see whether any of these substances are specified. It is important that the solvent you use to thin the epoxy will evaporate completely and fast, so that it does not remain in the epoxy when it dries, potentially weakening the bond further. The rule of thumb when thinning is that a little goes a long way. Add the thinner just a drop or two at a time to check how the viscosity changes. Don't add more than you absolutely need to get the right consistency, so the mixture remains as strong as possible.