Repairing Defects in Solid Walnut Slabs

If you can't make your patches disappear, do 'em up in style and make 'em look good. January 26, 2008

We are doing a large wine tasting bar and the owner bought several 2” thick slabs of walnut for the tops. The problem is there are large cracks throughout and a few places (near the root ball) with some pretty large voids. What would be the best way to fill these areas so they look nice with a natural finish? I am thinking some kind of tinted resin or epoxy. Am I on the right track?

Forum Responses
(Architectural Woodworking Forum)
From contributor L:
If you use the bar top pouring resins for the whole project, then all you will have to do is fill the voids first with the resin and then do your final pour. If you are using some other topcoat, then you will need to do a test of compatibility before you proceed.

From the original questioner:
Thanks. Actually, he wants a very natural, flat looking finish, so I don't think we will be pouring the top. He would like the defects to be as unnoticeable as possible (actually he would probably like them to disappear completely, given what he paid for the slabs). Is it possible to tint the pouring resin? I've never had any experience with that stuff.

From contributor R:
What I've done before for cracks in walnut is to cut slivers of walnut aligned (more or less) with the grain to fill the bulk of the crack and bed them in tinted glue, then plane or sand flush. Kind of like intarsia. I don't know how large the cracks are, so that might be a little fussy for your situation. It's a great color match, though. The voids you mention would be tougher, but the darker woods are more forgiving.

From contributor V:
Use a decent epoxy and add some walnut dust to it for color and volume, and fill the cracks with it, then level, sand and finish. Cured epoxy is inert, so is compatible with any finish you will use. You can even add color to the epoxy (search WOODWEB in the upper right corner) and turn it black if you like that look. Of course, try this in some scrap first so you know what to expect on the real thing.

From contributor W:
If you want them to look as good as possible, inlay them with solid wood from the same batch of lumber. You never mentioned the moisture content of this lumber. If you fill these voids with epoxy, the lumber could continue to move and your repair will be obvious.

From contributor V:
My feeling is that to try to match wood into these defects will be a bad scene. It absolutely will not match, and will look like so much bad workmanship - so it will be an obvious "miss." It is far better to have a dedicated difference - sort of saying "it's a patch" and be done with it. Let it sag below the surface a bit, tint it black, and it will blend and age well. Movement won't affect it unless your wood is too wet to use anyway. Nakashimas, previous and current, solved this one a long time ago, even calling attention to things with their butterfly keys.

From contributor Y:
I vote for the butterfly keys and black epoxy fill. Adds interest!

From contributor U:
Don't try to hide defects and voids in slabs. If he wanted a clean, no void, no crack look, he should have chosen a different material. Let them add interest.

From contributor T:
Use the butterfly keys. They not only look good, but they help prevent future splitting. I think future splitting is likely in a 2" thick piece of solid walnut.

From the original questioner:
All right, you talked me into it, butterfly keys and black epoxy it is. Now all I have to do is talk the client into it. I agree he should have purchased a different material for the look he wants, lord knows I tried to tell him. It would have been less expensive as well ($25 bdft, 6 slabs approximately 2’x14’). But the (paying) customer is always right. Thanks for all of the suggestions.

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

Comment from contributor H:
I believe that butterfly's are the best solution for this issue. However you may want to consider a natural filler such as crushed stone. I have used everything from coal to turquoise, depending on the look you are trying to achieve, clients’ tastes, surrounding finishes. Crush the stone and add epoxy. I would stress to use the butterfly's, they help to keep the joint from spreading further.