Fiberglass vs. Fabric

Ron Webb wrote:
Probably coating the entire plywood covered wing, inside and out with
cladding epoxy would eliminate the changes brought on by humidity
variations.

In furniture making it is considered important to finish both sides
of a piece of wood the same to maximize dimentional stability.
Otherwise the rate at which moisture enters or leaves one side
of the board is different from the other so that whenever there
is a rapid change in humidity one side swells more than the other.

IOW, I tend to agree with the statement above, but the same
would be true for varnish, shellac, paint etc, so long as it was
the same inside and out, and the wing was vented so that the
humidity inside the wing was the same as outside.

Of course the sun only shines on (and dries) the outside.



You may be familiar with "Wood/Epoxy Saturation Technique"
That has been used in boat building for decades?

How about "WEST systems" epoxy?

Yep - that's where the "WEST" in WEST systems comes from.

The wood gets soaked all the way through, so the wood is just there for
support, and it seems to last forever.

Hve you tried cutting through a sample? My understanding is that the
epoxy will not penetrate any deeper than 1/16" through side grain,
and it would be VERY unlikely to penetrate past the glue beneath
the surface veneer in plywood. It woudl penetrate farther up the
endgrain, but since epoxy hardens pretty fast I doubt it would get
very fat that way either. You can saturate a board with linseed oil,
or mos taly oil, by leaving one end in a bowl of oil overnight.

I BOILED some samples for 24 hours with no degradation other than a bit of
color change. Add light fiberglass over that...

Did you compare bending strength before and after? What is the
glass transition temperature for WEST system epoxy?

No question that it's good stuff, but it's not magic.

---

FF

I BOILED some samples for 24 hours with no degradation other than a bit
of
color change. Add light fiberglass over that...

Did you compare bending strength before and after? What is the
glass transition temperature for WEST system epoxy?


Well, actually I made up a long sample with 2 1" wide strips glued (with
fillet) together at a 90 degree angle. Then
I cut this into samples, each about 1" long. Then I took these little "T"
shaped samples, and subjected them to all sorts of things.

They were made of Finnish Birch 3 ply (3mm thick, but quite dense.) It
looked like it had penetrated to me - and they sure stayed together fine. I
boiled several of them, and broke them afterward. The wood gave before the
glue in all cases.

I've also tried this with 1/8" Okume. Same result, but that stuff is porous
enough that I'm pretty sure it soaks all the way through. I've been meaning
to try it with that unfinished mahogany indoor plywood. If that "soaks all
the way through" stuff works, it would be usable as a core, so I could use
much cheaper material (for boats at least).

As for the glass transition temperature, I think most epoxies are in the
140F range. After they cool they will return to much the same condition they
were before though. The extra cure may even be beneficial. That's just a
dull memory though. Correct me if I need it, but the boiled samples really
did stand up fine (I'm looking at one now).