Filling knot holes

If you plan to finish clear, epoxy would be a good choice.

Place a piece of duct tape on the back side to cover each knot so epoxy can't leak thru, then lay flat, back side down, and fill void a little proud with unthickened epoxy.

Wait 24 hours, flip over, remove duct, use some acetone on a rag to remove any remaining tape adhesive, then fill any remaining voids with more epoxy.

Wait 48 hours, sand flush on both sides, then finish of choice.

Lew

I saw a show home with all the woodwork done up in nicely stained knotty wood (Alder?) including kitchen cabinets. Any filler used was on the back side. Any cracked knots on the 'show' side were left alone and actually celebrated. It's like they wanted only knotty wood for every piece used and the cracks were part of the look.

Looked very nice without being messed with.

Pete

Black epoxy fills loose knots very nicely. Simply mix some black pigment or artist's oil color into the epoxy.

It looks remarkably natural. I've used it in cherry, white oak, and walnut, with equally excellent results.

I forgot to mention, plane or scrape the epoxy smooth once it cures. Epoxy doesn't always sand well.

Fill the knot slightly proud, scrape or plane smooth, apply almost any clear finish.

When I have knots in turned wood, I am worried about them working loose in the future. I use thin CA glue on them to bond the pieces together in a whole.

If there are larger gaps, I rub dark sawdust,(say walnut) into the voids, add some thin CA glue and sand smooth.

Be sure to put a coat of finish on the wood before using CA glue, any slops soaked up by the open grain will show after finishing.

I've also used colored epoxy, and it looks good too.

Old Guy

I like the other poster's recommendation to fill with epoxy. You can also use Bondo (for auto body repair). But, if you don't paint, you have the issue of matching the color of the filler with the wood. Any knot that has a black ring around it is probably loose, or about to become loose and fall out.