Filling Deep Knotholes

Techniques for filling knotholes before applying clear finish to a rustic Walnut table top. May 27, 2008

I'm making a walnut dining table for my clients. It is a somewhat rustic look. There are several knots (knot holes) that they want left in it, but that are too deep to leave the way they are. I have tried fiberglass resin, but could not get clear, and I have tried clear casting resin made by Castin' Craft and I can't get it to harden all the way on the wood. I have tried different amounts of catalyst, and it still stays soft. Any suggestions? The table is done except for these knots and finishing. I need to get it out of the shop.

Forum Responses
(Furniture Making Forum)
From contributor G:
Try (1) shellac stick or (2) tootsie roll epoxy (not clear, but can be blended to match the color in the knotholes).

From contributor J:
Personally I would highlight the knots by filling them with rock powder mixed with CA glue. You can get this from turning supply places in a variety of interesting colors and I think it looks great. You fill up larger knots with a combination of small rock pieces and the powder, then you can saturate that with the glue. You can also mix in some gold flecks and such if you like. Once it dries you just sand it down flush with the surface and it polishes up like a gem stone. Try it out on some scrap and I think you will love it. I first saw this done with jewelry boxes and I thought it was spectacular.

From contributor D:
We fill them with a 50\50 resin. Hardens crystal clear.

From the original questioner:
Thanks for the ideas guys. The rocks sound like something to try on a table with bigger holes.

Contributor D, is the 50/50 you're talking about the bar top stuff? I called the casting resin company and talked to their technician. She said the best product (their brand) was Envirotex, a 50/50 bar top resin. She told me to do the deep knots in two steps.

From contributor D:
Yes that's fine. West Systems is good also. Yes, on deep knots, do in two pours. Don't stir too fast and you won't have as many bubbles to worry about. Read the directions.

From contributor B:
Occasionally we have to make a radius moulding that looks like knotty pine. Since that presents a whole bunch of negative potential problems with running a curved moulding, we will insert knots after making a clear pine moulding. We'll drill or chop various shaped holes in the finished moulding and insert knots taken from other boards. You could do something similar here by drilling out the holes or just inserting chunks of dark knots into the existing holes. Most any standard adhesive will work.

From contributor C:
Have you ever used epoxy burn in sticks? It is more related to furniture restoration, but you can basically fill a ding in a finish, or in your case a knot hole, with relatively little dry time. The fill sticks are available in all colors including clear, and they dry rock hard. They are not the same as the wax fill sticks.

From the original questioner:
That sounds like a great idea. I've got them filled now on this project, but I'll put it on the back burner.

I've used shellac burn in sticks, but never the epoxy ones. On a knot this size I was afraid it would really make it stick out visually unless maybe it was black. Thanks for the thought.

From contributor K:
I toured a mesquite operation, and to fill voids, they mix copy machine toner with epoxy. They pour it into the void. Then they sand the surface flush and do the finish work. Simple, effective and attractive results. I was impressed.

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor W:
For knot holes use walnut sawdust, or a color of wood that matches up, and then we glue it. Mix it into a paste then push it into the hole and then take a wet (damp) sponge and wipe over the top surface to get excess glue off and to level off your knot hole. Then put your finish right over the top. This will work every time.

If you cannot find sawdust real fine like flour then look for a product called Famo wood. It is around $3.99 a quart and is a premixed sawdust and epoxy. It comes in different shades and is stainable also.