Filling Large Knotholes in Alder

Thoughts on dealing with the big knotholes in rustic-looking Knotty Alder wood. February 24, 2008

I'm using cabinet grade alder to build a bedroom set (bed, end tables, closet doors) for a client. It's very knotty at points, and in some places has rather large knot holes which pass clean through the boards. How best to patch these? I'd rather not just fill the holes with putty. Whatever I use needs to accept a stain.

Forum Responses
From contributor G:
If you don't want the look of knotty alder, why not use something else? Soft maple is quite similar. If you do want the look, fill your through and through holes with Bondo - it will accept stain - but why not color them darker so they look like knots?

From contributor A:
It's not that the customer doesn't want to see the knots. The problem is that the knot holes are large, and using putty to fill them does not seem the best way to go. Bondo is reddish-purple when mixed, and I think that some of the color would come through even after a dark stain. Does wood putty bond to dried Bondo? Maybe I could fill the bulk of the hole with Bondo, and putty over it with regular wood putty.

From contributor G:
You are over-thinking the situation. If the customer is okay with knots, just Bondo fill them. When it comes stain time, if they don't look enough like knots, just go over them with a Sharpie and darken them a bit. Bondo will take stain.

From contributor H:
I can understand the client not minding, in fact wanting, knots. But if it's a hole in the board, just cut the thing out or work around it. Is the client or you that penny wise? Consider the extra time it takes to screw around with that hole. That's not a savings. Cabinet grade? Sounds more like pallet grade. The Bondo or whatever you use will fall out, shrink, crack, fade over time.

From contributor W:
I have used T-88 epoxy with a stain added. It dries a translucent brown but there are powdered colors to darken it. The knot hole needs to be fairly clean to bond well. Or how about filling with Bondo, then using your router to cut out a butterfly inlay? There are templates available to cut the hole and the corresponding butterfly.

From contributor J:
Why not use clear lumber and paint in the knots?

From Professor Gene Wengert, forum technical advisor:
If there are not too many holes, why not drill out the holes to make them round and then glue in a wood dowel (epoxy glue)?

From contributor L:
Knotty alder has very large cracks and knot holes. The dealers call it "rustic," and they're not kidding! The first time I built a project with it, I thought the clients would freak out because you could see the inside of the cabinet through the closed door. Everyone I've built rustic cabinetry for has loved it.

I've never filled these cracks and holes before. If they ask for rustic, they get rustic. However, if I was doing this for myself, I would fill the voids with black epoxy, let it dry, then sand flush. I think the knots and cracks would look great leveled and the black epoxy would really highlight these areas. I've tried to sell this a couple of times, but haven't found the client who is willing to pony up for this look.

From contributor U:
I've done a lot of work with knotty alder. It's becoming a very popular wood. I fill my large knot holes with a mixture of clear epoxy and sanding dust. It takes the color of the stain, while not making the knot look patched. Do some samples to get the right mixture.

From contributor W:
If they wanted knots, then they will love alder knots, even if they are see-through. If not, black epoxy is great... and by the way, you can tint your Bondo darker with an ounce or two of color from your local paint store. Big paddle bit like you use to mix Thinset, a drill, and about 15 minutes to mix a gallon. It will look like it's not mixing for about 10 minutes, but during the last 5, it really mixes.