[pianotech] Epoxy Filler

[Ron Nossaman]

To whom it may concern, or anyone interested,

Yesterday, I filled a set of rib mortises out in the shop, preparatory 
to routing new mortises for a new and considerably different rib set, 
and installed a cutoff bar, fish, and further belly rail bracing. I used 
thickened West System epoxy. In the past, I'd used maple floor (band saw 
and sander sweepings) for a filler and thickener. It works nicely to 
increase the volume of the epoxy, but I don't like how the epoxy drains 
out of it as it sits. Adding something of a smaller particulate, like 
high density filler or colloidal silica tends to keep the epoxy in the 
wood flour, but it seems like a waste of materials when all I want is a 
cheap filler and volume increase that doesn't separate and doesn't kill 
the strength  and toughness of the epoxy altogether. So yesterday I 
tried good old non-exotic general purpose wheat flour. I used my wood 
flour for bulk, and enough wheat flour to make a peanut butter viscosity 
mix for bedding the cutoff bars and bracing, and more like yogurt to 
pour into the mortises and plate lag holes with my highly sophisticated 
duct tape dams. It handled beautifully, and the epoxy stayed suspended 
in the filler with no indication of it settling out.

When I leveled everything this morning, I was very pleased with the 
texture of the cured mix. It's less brittle than straight epoxy, but 
still quite tough, and works as well as anything I've tried, better than 
most, and cheaper than almost anything.

If you have a need, I recommend you give it a try. Self rising? You're 
on your own.

Ron N