Filling Knots with Epoxy

I picked up this beautiful piece of walnut recently. I just couldn't not buy it. I don't know what I'm gonna use it for yet. Some kind of a tabletop. But one of the problems it has is that bark is just a little bit loose, and I want to make sure that that bark stays in place because that's such a nice feature of it.

The other thing is it's got some knotholes, it's got some cracks, and I want to take care of those. I don't want to just leave 'em as cracks. So we're gonna fix this. We're gonna take care of this with epoxy, more specifically, this is what's called casting resin. If you go to a hardware store, if you go to a home center, and you get two-part epoxy in the syringe, you squeeze it out, you mix it, it's really thick compared to this stuff.

You'll see that in just a second. With this, benefit is I can pour it over the top of this, and it's really gonna flow down into that void, and it's gonna do a much better job on this than trying to pack the regular two-part epoxy in there. So casting resin, it's available online from a variety of sources. Follow the manufacturer's directions about mixing it. There are some pretty persnickety directions here about what you do to get it mixed.

Now, this goes all the way through. When I pour the resin, I don't want it to go all the way through. So we're gonna build a dam in the form of masking tape. And what I'm doing here is I'm choosing my good face, bad face. Actually my kid, Jenny, chose good face, bad face.

So this, by putting the masking tape on this side, is becoming the bottom of this board. All right. A little mixin'. And this stuff, when I pour the hardener in here, you'll see it's got a little bit of a yellow tone to it, but it doesn't when it's cured. When it's cured, it'll be perfectly clear.

50/50 mix. The other thing that's different between what I'm working with here, this casting resin, and a syringe of most two-part epoxies is that the cure time, the tack time, is really long. This is gonna sit overnight to be completely dry. So as a result, we don't have to be in quite a foot race here with the glue in order to make this work, where if you were working with five-minute epoxy right now, you'd have to be working really, really, really, really fast. All right, here's the easy part.

I'm just gonna pour , and let it settle down in there. We're gonna fill that void right up. And this is where the fact that it'll flow on its own is a good thing. So one of the things you probably notice is there are a lot of bubbles in there, and that is a natural byproduct, of course, of stirring this epoxy around. We're gonna fix that, and the form of fix, I'm gonna do it with a propane torch, but you can also do it with a hairdryer or a heat gun.

We need heat is what makes this work. What I'll do is I'll light this up and then, brrp, pass it over the top. Watch closely. It's gonna just take all the bubbles right out of there. This is gonna be so beautiful when it's done.

Now here's a qualifier. On a pour, especially where all this bark is right here, watch that, oop, see a bubble just come up? Watch this over time because it's gonna continue to bubble. That bark is a really rough, irregular surface. So we've got air trapped down in there, and you just want to come back and look every few minutes.

If there are new bubbles, hit it with heat again; new bubbles, hit it with heat again. Eventually, as this stuff cures, that'll stop 'cause the bubbles can't come up anymore, or all the bubbles that are gonna come up will have come up. So look at it every once in a while. We're gonna let this cure, and then, once it's dried, come back and look at leveling the surface out so that we get rid of the excess epoxy and just what that's gonna look like. When you're using epoxy or casting resin to do this kind of stuff, do make sure you let it dry, dry, dry, dry, dry.

This stuff has actually been sittin' almost two days since I cast it. One of the things that's really nice to do is to keep the mixing pot, and there'll be a little bit of epoxy left in that. And you can watch that to see how hard it's getting 'cause, of course, we don't know what's happening down inside here, layers and layers and layers below the surface we can touch. So best bet, if you're not sure, give it more cure time. Does take a while to completely cure out.

Now, we've got epoxy that's standing proud of the surface. This is where we have to introduce the S-word. We have to do a little bit of sanding. I've also used cabinet scrapers on this, and it works pretty well. Cabinet scrapers work pretty well.

Downside to sanding the epoxy, you do tend to go through abrasive fairly quickly 'cause the epoxy clogs it just a little bit. So I'm gonna start with a belt sander. Then we'll move to a random orbit sander, and we'll just kind of talk through the steps it takes to get this lookin' really good. You can really start to see the dust on my glasses. You can really start to see the gain that we're gettin' from this epoxy because what we had here before was a bunch of bark that was really ready to fall right out of the slab.

Now it's been stabilized with the epoxy. What needs to happen is this is 120 grit on the random orbit right now. I'll keep taking that up to progressively finer grits. We want to sand that up to about 400 or so. Then when we get finish over the top of this, that epoxy is gonna really look great inside that bark inclusion.

So epoxy, casting resin, is a great way to save a beautiful board like this that otherwise would have a huge hole in it and wouldn't look that good. Give it a try the next time you run into these kind of inclusions in the wood for your projects.