Thread: Glass strength

Assuming a good wet-out (which often takes at least two coats laid on hot), then fill-coats are cosmetic, from what I'm aware. Neat epoxy doesn't add much in strength in this application, it's really there to bond the glass.

That said, a decent thickness of epoxy helps to form a moisture barrier, and a smooth glass surface is less likely to trap dirt. Up to you.

I know of a few people who recommend letting the cloth weave stand proud, and paint it as a form of non-skid on decks, so it can't be too bad of a thing to leave the weave open!

The glass gives the mechanical strength and the epoxy the chemical bonding, more resin will not add any strength , unless more glass is added at the same time.


Jeff

G'day Chris
Might be a bit late for you if it has already cured...
The tensile strength in glass is unbroken strands. Sanding through the outer pox
into the actual glass cuts those strands, weakening it, and admitting water into
the glass matrix.
If you want a glossy smooth paintable surface, you add extra layers of pox
before it fully cures to build safe sanding thickness above the glass.

On the other hand, if all you are after is abrasion resistance, cut strands only
reduces the thickness of glass working for you. Well sanded & another 2-3
layers of pox applied over it to re-seal it will retain much of that property.

Remind us again - what's the boat?
regards
Alan

Alan,
It's never too late. It's a SOT kayak. Jem Watercraft Sabalo. I'm in a constant weight versus strength argument. I want to keep the weight down as I will be transporting it on top of the 4x4, but I want to make sure it is strong enough to use in the surf. My gut feel is to put the extra epoxy on just to be confident that I've made it as strong as I can. I guess I have to weigh up the extra effort in man handling it, or the extra effort of taking it apart to fix something.
Cheers,
Chris

Epoxy = weight rather than strength.
MIK has done the numbers &, from memory, thicker plywood comes out better in
strength vs. weight, rather than adding glass. Glass = strength on the outside
of the ply where it is needed, but more glass requires more epoxy = more weight.
I think he put the data up in his web-site.

If the boat was designed for flat water, & will cop a caning in surf, maybe
need to be thinking in terms of internal girder/s to maintain overall shape &
rigidity? If top & bottom can be crushed together, the boat will tear apart at
that point, glass or no glass.
cheers
AJ