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(Backyard Renegade) wrote:

I guess I was more trying to make a point with my simple terms. That
point being, I always take an extra minute to rough the surfaces up
too, especially in structural areas. For areas that will be hidden in
a joint or filled later I use two tools for roughing. One is a heavy
grit offset grinder and when I can't get that in there or for more
precice work I take an old jigsaw blade, add a little bend and draw
the blade over the surface in a cross hatch pattern. And just to take
it one step further, I always mix up a small batch and throughly wet
each surface then add filler to the rest of the batch and paint or
spread it on the wetted surfaces then fasten or clamp.

I have always reccomended using as little filler as necessary to hold
the goo in place. A lot of my construction calls for epoxy to act as
as adhesive (glue?, simple terms again) as opposed to just filler for
glass... I have always explained it as "let the epoxy do what epoxy
does"... anyway simple terms again, but now I have a better
understanding as to how it works.
Thanks, Scotty

I read all these sort of things years ago when I started using epoxy
and so I did some tests. I made a series of lap joints where the lap
was four times the thickness of the wood. I used mahogany, red oak,
and fir. I made pieces planed smooth, fine sanded, rough sanded, and
rough sawn. Finally, I tried tight clamping, and loose clamping. I
did coat the pieces with unthickened epoxy and allowed them to soak up
for 10 minutes before adding thickened epoxy and clamping. I was
surprised and pleased to find that in all cases the joints were
stronger than the wood.

After having accidently left a block of wood next to a puddle of
penetrating epoxy (Syatem Three Clear Coat) one day, I found the next
day that it was bonded to my work bench. So I experimented and found
that I could even make a good joint by clamping pieces of smooth and
flat wood together dry and dribbling Clear Coat on the edge of the
joint, letting it suck in by surface tension.

So, using clean wood and good epoxy, well mixed, I don't worry about
how smooth the surface is as long as I have full contact in the joint.
With glass over pre cured epoxy, it generally has to be washed to
insure you don't have an amine blush which will interfere with
bonding. Sanding won't remove the blush, only spread it around unless
you remove the whole surface. The same care should be taken with any
epoxy joint over pre cured epoxy.

Al