Epoxy to fill knot voids at edge?

[manyirons]

Hi all,

I've been building a captain's bed for my son out of some old reclaimed pine. Due to the limited amount of wood I was not able to avoid having some knots at the edge of a face frame. One of them is big and really shabby, with quite large voids. I'd like to fill it, and I'm thinking epoxy would be the best choice. I really don't like the look of wood filler when it gets any bigger than a BB.

Assuming you agree that epoxy is a good choice, how can I apply it? At the edge of the board it's going to just run out, so I need to block it while it sets. The blocking must not stick to the epoxy. I don't have sheets of teflon, other than teflon plumbing tape. Is there something else (like HDPE or polyethylene, which I didn't try it yet) that will work instead? Alternatively, if I let the expoxy get proud of the surface can I sand it down and hope to apply water based Minwax Varathane and not see the sanding marks? In that case I can block it with a few strips of wood and just plane/sand them away. Actually, I'm inclined to think that's the best approach, so I may try it on some scrap while I await more brilliant feedback from you guys.

If there's no other choice I can cut the offending chunk away and glue in a replacement, but it'll lose a lot of character and just plain won't look as good as I know it can.

I hope all this makes sense. Thanks for your advice.

- Owen -

[basilisk]

take a piece of scrap and rub it with wax and clamp it over void, will pop off easily after the epoxy sets.

basilisk

[Steve Turner]

That should work, but I wonder what the remaining area around the knot hole looks like (perpendicular to the backer board). It's likely that the epoxy will "sink in" to the wood and NOT be proud of the surface by the time it's cured, so what I like to do is build a "dam" around the affected area with simple latex caulk, which allows you to overfill the area with a "lake" of epoxy and plane or sand it down after it's cured. You're going to need some pretty fine sandpaper if you don't want to see sanding marks after you're done; lots of guys here claim that for wood they never go finer than 220 but for epoxy I think you're going to need at least 400 (maybe 600) or you're going to see scratches...

[joeljcarver]

Another suggestion: Cut away around the knot and patch the wood with a scrap of the same stock. Try to match the grain as best you can. I think that would look better than a lump of epoxy.

[Sonny]

If your scrap pieces have knots, use those knots to fill the voids and epoxy them into place. If you don't have knots in some scrap pieces, maybe you could stain some scrap to "make" knots, and insert them into the voids (epoxy into place).

I vote for the waxing suggestion, for your "framing in" of the filler.

Sonny

[Gordon Shumway]

You could remove the offending area and replace it with some scrap material that the grain matches the affected area's grain. Repairs like that are often invisible.

If you're concerned about losing some character why not create a "Dutchman" patch for that area. One that would repair the area but not attempt to conceal it's existence. That way you could have your cake and eat it too.

Gordon Shumway

When you subsidize poverty and failure, you get more of both.

[GROVER]

Another way to approach this is by covering a piece of scrap with kitchen waxed paper. This suggestion is a variation of previously mentioned ideas.

I also like the dutchman technique. Norm has demonstrated this on several shows and it seems to produce a satisfactory solution to the problem.

Joe G

[SonomaProducts.com]

Epoxy sands out really well so you could just build up a dam using tape and sand it all away later.

I like the concept of doing a patch using similar grained material. In a very early job (16-17 years old) at a rustic furniture factory when we had bad knots in Pine we would use a chisel them out and sand a plug to fit and just yellow glue it in place. You would be amazed how well it blends.

Another option is to just break out all the loose material and grind and sand the edges smooth. I actually always like to have some little hidden wild edge on any of the better furniture I build. And when it is for me, I like it to be visible.

[dadiOH]

Add Cab-o-sil (fumed silica) to the epoxy to thicken it. Make the mixture about peanut butter consistency. You can get Cab-o-sil (or Air-o-sil) at most any place that sells epoxy other than HD, Lowes, etc. Marine stores or Surfboard shops may be a good bet. If not, internet.

You can use clear packaging tape to help shape the fill. Best to apply it to another piece of wood, clamp that to what you are filling. ______________

Epoxy doesn't sand real easy. A cabinet scraper works pretty well. As far as seeing marks, depends on how finely you sand. Just like wood. ________________

IMO, a large epoxy fill isn't going to look good...it will look like a yellowish chunk of glass. Or dark glass, depending on how deep the fill is.

My own preference is to use wood...chips (as from a planer), coarse dust (saw dust) and fine dust (sanding dust) mixed with glue to build up a surface that is flat but shows irregularity because of the mix of particle size. It may or may not be acceptable "as is"; if not use an artist's brush with paint - any kind of paint - in varying colors to draw in a pattern and colors that matches the surrounding wood. Then top coat. Do it right and you'll never know the knot was there.

BTW, if the knot has a dark edge, cut that away before filling and coloring.

[manyirons]

I actually have most of the original knots still in place, but some of them are loose and there's wild grained gaps up to half a centimetre across near the centre plug.

I like the wax idea. I'm going to try it on some scrap and see just how easily it pops off. I already have a few dutchmans replacing the ugly man-made tears the contractors made when they ripped this stuff off the walls. The natural "defect" seems more appropriate to preserve. But I think I'll pre-seal the wood so it takes the finish before I embed wax into the pores.

epoxy I think you're going to need at least 400 (maybe 600) or you're going to see scratches...

I'm hoping to avoid all that by applying finish on top of the epoxy, letting it fill in the scratches, but I've never tried that before. Won't it work? I've seen how smooth you can make it using finer and finer grits, but I'm hoping it's not necessary. I've got the fine grits I need, and given the small area it's not really such a big deal if I have to go that route. I'm also hoping to avoid a lot of experimentation just by asking you guys for your experience, but I'll do what I must, and learn what I will.

Thanks for the great suggestions so far. It's exactly the kind of feedback I was hoping for!

- Owen -

[Lew Hodgett]

------------------------------------------ Since the knot is "shabby" anyway, knock it out so you can get back to some structurally sound wood.

You then cover the sides of the knot hole with duct tape to form a temporary dam.

Mix up some decent epoxy and thicken it with some micro_balloons to the consistency of mayo.

(Using Cab_O_Sil to thicken epoxy is like getting a sentence to wear a hairshirt while sanding. You don't want to go there.)

I might add some carbon black an make the patch an accent, but that's just me.

If the knot is much larger than about an 1-1/2" in diameter, I make two pours to keep the heat down.

Allow to cure for 2-3 days, then remove tape and sand.

You now have a structurally sound timber.

If you want to cover the patch with a "Dutchman, go for it.

C Groh, want to jump in on this?

Lew

[manyirons]

I did a test on a scrap mortise with a peg hole in one side where I poured in the 5-minute epoxy, and the waxed board pretty much did the job. A little shred of it was left behind, but it was quickly sanded away, to 320 grit. Scraper didn't seem to make any difference over sanding, but it sure is hard to remove significant material. I applied finish over top and it cleared right up so I'll probably stop at 220 next time. It's drying now, and I'll see in the morning whether it bonds and takes another coat. The only thing I think I must watch out for is over sanding, since the epoxy is much harder than the pine and it ends up a bit proud. In this case it won't matter, but someday it might.

- Owen -

[dadiOH]

I've used Cab-o-sil for 40 years, sanded a lot, nary an itch. Fiberglass, yes, fumed silica, no. Nothing wrong with micro baloons if you don't mind the color. Ditto wood dust. Ditto talc (but it's heavy, no big deal for a knot).

[Jay Pique]

With the 5-minute epoxy there's a window of time after it has set up firm during which you can slice it off with a sharp plane blade flush with the surrounding wood. It's one of two uses I've found for the Lee Valley flush-trimming plane, the other being to slice off polyurethane glue squeeze out.

JP

[Steve Turner]

That's true of pretty much any epoxy, not just the 5-minute variety. BTW, most

5-minute varieties yield pretty crappy results in terms of strength and holding power; you're better off using the slower-curing epoxies if you want the best quality. Most commercial grade epoxies I've used that yield these kinds of results take at least a half hour to "kick" (get thick and gooey), and about 4 to 6 hours before they can be sliced and planed (like you mentioned), and at least 6 to 8 hours before they can be sanded, preferably overnight. Good epoxy can't be rushed.

[Tom Dacon]

I'd suggest mixing up some epoxy in a cup and adding sawdust from the same kind of wood until the mixture is pretty stiff - it should stand up in peaks and droop slowly if at all.

It'll still sag some while it's curing, so all you need to do to keep it in shape is to make some of what used to called "dams": take a couple pieces of scrap wood, cover them with a strip of smooth tape, and then wipe a thin film of white grease on the tape so it'll release after the cure.

Do the knots one at a time. Fill the voids with a spatula, tool it until it's a bit proud all around. Clamp a piece to the underside face and another to the vertical edge to keep the stuff from drooping out of the patch. Finally wipe off the squeezed-out mixture and tool the upper face until it's just very slightly proud (epoxy doesn't shrink to any appreciable extent). Work reasonably quickly.

After a while, while it's still just a bit green (not yet cured rock-hard), pop off the dams, give the edge and the underside face a wipe with a small bit of paint thinner to remove any trace of the grease, and block-sand as necessary with a coarse paper like 60 or 80 grit to make it flush. Let it finish curing, and then go over the faces and the edge with finer grits until you like the look.

The filler will come out darker than you expect, so do a test on a piece of scrap to see if it's to your taste. If not, there are other special-purpose fillers for epoxy which come out white or gray, and then you can take a brown sharpie and just draw over the patches to try to match the grain, or stain it to suit yourself.

For something like this, I use West Epoxy. You can get different catalysts which cure at different speeds. For this I'd use slow catalyst so that I'd have plenty of time to work the patch before it started to stiffen up. Hardware store epoxy might not give you that flexibility.

Tom

[manyirons]

Well I've filled all the knots now, and to my eyes they turned out great. I pre-finished around the sites to seal the pores, and after a few hours of drying I made dams out of small strips of wood into which I rubbed paraffin. The epoxy was too thick to flow into every single crevasse, but it didn't have to. It just had to hold the biggest chunks in place. So now that's done, and the dams came off easily, leaving behind perfectly flat and flush epoxy surfaces. I've got a couple more dutchmans to do, and then the whole face frame will be ready for finishing and installation. Yeehaa!

Thanks again, everyone, for all the tips!

- Owen -

[Lew Hodgett]

----------------------------------------- After sending a few thousand hours on the business end of a fairing board, to fair out a boat hull, get back to me.

Some where along the fairing process, someone is bound to mix up some fairing putty using Cab_O_Sil.

Once you have had to fair out Cab_O_Sil.with a fairing board, you will NEVER want to do it again.

DAMHIKT.

MIcro-ballons are white unless you are referring to pheonlic balloons used by the race boat builders because of their very light weight.

Those are brown and VERY expensive.

Wood dust and talc for fillers?

OH FUCK.

Why waste good epoxy by using garbage fillers?

A 30# bag of Dic_A_Perl (HP-500) which is 8 cubic feet is about $25.00.

Unless you are a boat builder, that's probably a lifetime supply.

Lew

[Nemo]

Lots of excellent advice in this thread about epoxy, but here's another approach: I don't know if it's because I know it's there, but I find that my eye is always drawn to an artificially-filled knothole. It never quite matches up to the grain around it. So -

If the knots are loose or ugly, knock them out. Walk the woods and find a branch of a similar wood. Whittle it down to a fair fit, spot on some glue, and hammer it into place. Trim and sand - it'll be just like Nature intended

- a knot, but a nice-looking one.

Nemo

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[Steve Turner]

There have been many cases where I've worked with knotty wood and chose to leave the knots in place because I felt that removing them or plugging them would take away from the natural look. What's worked well for me is to saturate them with a good slow cure epoxy (like System Three, perhaps with some black pigment mixed in), to lock them in place and fill in all the voids that would compromise the structural integrity. This can actually wind up looking very nice, depending on the type of wood and what kind of finish you apply to it.