Filling holes/cracks in walnut

[Guy Dotan]

I'd love some advice about the best way to fill large cracks/knots in Walnut. I've been using system 3 epoxy + medium harder + black dye. While I like the look of the black filling, the issue I've been having is small air bubbles. Some of the bubbles are on the very top of the surface, and some are exposed after light planing, leaving tiny holes on the surface.

Any suggestions?

[John C Bush]

SOP for filling voids with epoxy. I learned from the knowledgeable ones here that fanning a propane torch flame or heat gun lightly over the epoxy surface "pops" the bubbles and flattens the surface. Overfilling a little helps. More bubbles tend to migrate up so you will likely need to watch and repeat.

[Prashun Patel]

Small voids: over-fill, then scrape/plane/chisel flush
Large voids: Under-fill slightly. Let dry. Overfill next day. Scrape flush

[Roger Bull]

To add to what John and Prashun said, there is a tip that I'm going to try soon. I have a bunch of walnut voids to fill. Heating the wood prior to filling with epoxy supposedly reduces bubbles that come from the wood as it heats up from the epoxy. Pre-heated wood will be cooling when in contact with the epoxy (exothermic reaction) instead of heating and in theory won't push bubbles into the epoxy. Of course if you do multiple pours this is a non issue because the first pour should seal all the wood it comes in contact with.

I use West System epoxy and have not used System 3. I use a slow hardener which gives lots time for the bubbles to rise to the top. I always leave the leftover in the mixing container to verify hardening and it is always bubble free. Does the medium hardener make yours faster setting?

[Dylan Wyatt]

I have done a couple epoxy inlays, all cut with a router, never filling knots. However, the best process i found was to clean the area well then I taped around the perimeter of the area to be filled and sprayed the area with two light coats of polyurethane from a rattle can. This seals the grain to avoid having the air from within the wood coming up through the epoxy during the curing process. I used System Three MirrorCoat epoxy with glow in the dark dye for my piece. Once I poured the epoxy into the area to be filled, like John I used a propane torch to draw the bubbles to the surface and they will pop. Trust me, it was one of the coolest things I have seen watching all of the bubble rise out of nowhere. You will get a feel for how far away to keep the torch and you just fan it back and forth over the void. I did an unbelievable amount of research before completing the pour because I had one shot to get it right this left me with a bubble free surface. Here's a picture of the main pour I did with the glow in the dark powder in the resin.380275Hope my experience helps! It was a painstaking process for me because I'm not so patient but it is well worth it! I look forward to hearing other people's solutions.

[Terry Therneau]

An old time method is to use a shellac stick. I found it in Tage Frid's book and have used it on walnut, very successfully. You melt the shellac into/onto the fault, then sand when done. You can buy the sticks, I made mine.

[Neil Gaskin]

I’ve had good luck using a light coat of abatron wood epox after west system to fill small voids/air bubbles. It has a Pladough consistency. I’ve used the same powder dye in both. The color match has been excellent. If you really get right up on the filled area you might be able to see the difference but you have to be inches away. From normal viewing distance I’ve not been able to tell a difference btw the two products.

The real advantage I have found is that it’s only a two-step process. Fill with West systems, Sand flush, then the abatron wood epox. Because of the consistency of the abatron I’ve not had to do repeated fills. When I just use west systems that can sometimes be three or four or more pours to get rid of all the air bubbles. There always seems to be that one last tiny air bubble that pops in final sanding

Maybe I could mix the west systems better to eliminate Bubbles from occurring but some of it I think it’s just The nature of liquid epoxy versus the thicker consistency of wood epox.

I’ve also found a heat gun better and more controllable then a torch For heat application.

[Guy Dotan]

Many thanks to all. I think I’ll try the epoxy + wood epox method.