Epoxy as a void filler

[Prashun Patel]

A couple of the joints on a chair I'm making have tiny gaps that I'd like to fill with tinted epoxy.

I don't want to inhibit the area around the joint from absorbing finish.

Material: walnut
Finish: Oil/varnish blend. I'm not dying or staining.

1) Should I tint the epoxy with dye or sanding dust?
2) Should I wait until the first coat or two of finish has been applied so's to seal the surrounding grain from absorbing the epoxy?
3) Is shellac or wood glue a better choice than epoxy?
4) Is there a good way to thin epoxy to make it easier to get into the joints?

Any help appreciated.

Shawn

[Jamie Buxton]

I use epoxy from West Systems for this. It is intended for fiberglassing, so it is thin enough that it easily flows into cracks. In fact, the usual issue with it is that you think you've filled the crack, and then it flows further into the crack, leaving a void at the surface. I've learned to leave a puddle on the surface to be a reservoir to avoid this issue. However, this does mean that after the epoxy cures I need to scrap and sand the puddle off.

I tint the epoxy with pigment. The place that sells you the epoxy will probably have the pigment in little tubes.

The result is monochromatic. That is, it doesn't really look like wood. That's okay in some spots. For instance, it looks like the dark streaks that are sometimes present in cherry, and nobody notices. But for some other woods -- oak, for instance, the match isn't as good. Sometimes sanding dust in wood glue works better. And, of course, sometimes you're better off putting in a dutchman of real wood.

[Prashun Patel]

Thanks, Jamie. The joints are in awkward positions, and if my epoxy is on the thick side, I'm not sure I'll be able to aim it in the hole - and JUST in the hole. I'm picturing having to apply it with a toothpick and having it glob over onto the surrounding wood.

The big q is how to protect that surrounding wood from getting stained - or will it just sand off easy in those spots without tinting the underlying wood?

So, to fill before or after finishing; that's the question.

[Jim McFarland]

I've used Waxilit from Lee Valley to protect surrounding wood from epoxy and it worked very well. I used Heet (auto fuel treatment) to clean the Waxilit and then finished as usual. As with any finishing, recommend you test the process on scrap 1st!

http://www.leevalley.com/wood/page.aspx?c=2&p=32092&cat=1,43415,43440

Woops, seems LV doesn't ship this Oct-Apr because of freezing issues.

[Jim Terrill]

When I was building boats, we would use slow set 2-part epoxy and the sanding dust of whatever wood we were working at the time. This way there was no color to leach into the surrounding wood, make it a little bit higher and sand to level.

[Prashun Patel]

Thanks, Jim and Jim-
Jim, when you used the epoxy+sanding dust, even though the color does not leech into the surrounding area, did that area appear lighter or darker once finished?

[Jim Terrill]

slightly darker, almost like the wood had been wet down, which makes sense, you basically have dust that you wet with epoxy and it dries in that "wet" state.

[Scott Holmes]

Give your project a couple of finish coats then clean the hole/crack with acetone and apply the slightly darker epoxy no sawdust. It will look like sawdust in the crack.

[Prashun Patel]

Muchas Thanksias.