Epoxy to fill knot voids at edge?

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"Steve Turner" wrote:

Same trick,using black epoxy to fill voids, as the people who work with mesquite.
A little tip, you can thin the mixed black epoxy with denatured alcohol (About 5% max) to get better penetration without weakening the bond.
Lew
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On 7/11/2010 6:44 PM, Lew Hodgett wrote:

I think whether or not you can do that must depend on what brand of epoxy you're using. I've tried that with Bondo brand marine epoxy (which I really like) and wound up with a rubbery result that would never cure hard. I may have used more than 5% though; not sure. I've never tried it with System Three, which is the other brand I use most often, but it's already sufficiently thin that I haven't felt the need to cut it any thinner.
And I too have done the black epoxy on mesquite thing; I do live in Texas after all. :-)
--
"Our beer goes through thousands of quality Czechs every day."
(From a Shiner Bock billboard I saw in Austin some years ago)
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"Steve Turner" wrote:

My choices of "Good Epoxy" never included Bondo so can't comment.
System 3 has good stuff, have used thousands of gallons of it.
The alcohol add can be tricky, a little goes a long way. ------------------------------

Strictly for special applications. ----------------------

Black epoxy works well with several woods, not jut mesquite.
Lew
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On 7/11/2010 10:51 PM, Lew Hodgett wrote:

Yeah, with a name like "Bondo" one might conjure up the idea that it's low-quality automotive body putty crap, but it's really quite good compared to most locally available junk called "epoxy". This is the stuff I'm talking about:
http://www.jamestowndistributors.com/userportal/show_product.do?pida47
It has nice nice working qualities and excellent strength (and a nice caramel color too, which blends very nicely with wood without the need for additional colorants), and I was planning on buying some more when this batch ran out, but it looks it's been discontinued...

Since you've already tested alcohol with System Three I might try it sometime if the need arises. I'm not sure it would work with their T-88 product though; that stuff is a bit of a different animal.

Yep. You see it a LOT with Mesquite though because it's so hard to find any decent quantity of wood that isn't full of checks and voids.
--
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Add On:
"Steve Turner" wrote:

If your alcohol had any water in it all bets off.
Rubbing alcohol won't cut (Too much water).
Lew
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Or hit it with a heat gun. The heat makes epoxy very runny and it soaks right in.
-Steve
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Decent epoxy, filled with phenolic microballoons to the consistency of peanut butter. For paler wood, silica microballoons with a dye. You can apply this with a popsicle stick, you don't need a mould. Microballoon filler is useful because it's easy to sand afterwards.
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manyirons wrote:

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.
--

dadiOH
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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
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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 -
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