I’m thinking of using a long-setting (30 minute) epoxy to make up some glue joints, and I want to tint the epoxy to match an existing finish so that the glue joint is less obvious. I would like to use an oil-based, pigmented stain as the coloring agent. Will adding this stain to the mixed epoxy in any way compromise the bonding strength of the cured product? – John Cusimano
Tim Inman: You can tint epoxy with dry rare-earth powdered colors. Do NOT tint with anything like oil paint pigments or acrylics. Do NOT use stains or solvents either. Do NOT add aniline dyes! They will turn the epoxy into rubber sometimes. Epoxy mixtures are critical. Do it right and you get what you want: a strong bond and an excellent hardness. If you mix solvents or other oily, gooey things into the epoxy, you might very well get something you do not want.
Personally, I usually default to a little very fine sanding dust from the wood I’m using as my source of color. It doesn’t take much to do the trick. Compare epoxy to glass. When you view through the glass the ordinary way — as if looking through a window — the glass seems clear. But, when you view through the glass the ‘’edge” way, the glass appears to be green. The color of the glass concentrates in the deep cross-section view. Guess which view will be the “ordinary” view with an epoxy repair? Right! You’ll usually be looking into the deep cross-section of the adhesive just like the glass — and whatever color you added will compound in its intensity. Go easy and always do a test before launching on your project. Epoxy, once in and hardened, will have to be sawed or cut out to be corrected.
Chris Marshall: I’ve have good luck using Homestead Transfast® powdered dye mixed with 5-minute epoxy as a wood filler/colorant. It’s cured hard enough for that application and seems to stand the test of time pretty well. But, I’ve never used that mixture as adhesive to bond wood together—just as a filler—so I can’t attest to its bond strength. Fellow readers, any advice for John you’d like to share? I bet the boat builders/restorers among us could add to this conversation! Please chime in.