FR wrote:
He said.........

I am using West system epoxy. The material is about 6 mos. old. I am
bonding over fairing putty that was used to level the surface prior to
putting the fiberglass down. It was a clean and course surface. The part
I don't get is that it didn't even stick to itself. I did some repair
work using this epoxy and DB1808 and it is solid as a rock.



You have discovered that the 6 oz finely woven fiber glass that is commonly
sold by "fiberglass supply houses" is terrible when it comes to adhesion
properties. I have found this to be true regardless of the resin type
Epoxy, Vinylester or Polyester.

I think it is attributable to the tightly packed and twisted tows used to
make the material. It does not allow for good saturation.

Next time use a DB1208 and you will get the same results as the DB1808 and
save a bit of weight. The glass mat sewn to the double bias strands offer
good saturation and great adhesion and a superior water proofing layer.

I know of very few "pros" who use this stuff in fiberglass work but for
some reason it seems very popular with do it yourselfers.

In 28 years of fiberglass boat building with five different companies I have
never used this product in a commercially built boat.

My advice is to stay away from it unless your are building model boats.

That's interesting, as I know literally hundreds of people that have
covered wood (S&G or strip) kayaks and canoes with 6 oz. fabric and
epoxy of various brands with zero problems. I've used it in multilayer
kayak repairs with zero problems. I suspect that there's more to this story.

Likewise, however, I did a test with the 6 oz cloth and 17 oz biax. I
laminated two pieces to a piece of plywood side by side using the exact
same epoxy. After 24 hr. curing in the house, I was able to rip the 6 oz
off the wood, but not the biax. I suspect something was wrong with the 6
oz material. I bought new material (10 oz) and I'll try that.


That's interesting, as I know literally hundreds of people that have
covered wood (S&G or strip) kayaks and canoes with 6 oz. fabric and
epoxy of various brands with zero problems. I've used it in multilayer
kayak repairs with zero problems. I suspect that there's more to this
story.

Dan wrote:
Likewise, however, I did a test with the 6 oz cloth and 17 oz biax. I
laminated two pieces to a piece of plywood side by side using the exact
same epoxy. After 24 hr. curing in the house, I was able to rip the 6 oz
off the wood, but not the biax. I suspect something was wrong with the 6
oz material. I bought new material (10 oz) and I'll try that.

Unfortunately, 17 oz. biaxial fabric is WAY too heavy for a lot of
applications.

Also, 24 hours is not adequate cure time for most epoxies before you
torture test them. It's enough to allow you to shape/fair them, but full
curing takes several days at a minimum, unless you're working in
unusually high temps. At low temps, a full cure can take weeks.

Perhaps there was something wrong with the fabric you had, but it's
certainly not a universal problem.

That's interesting, as I know literally hundreds of people that have
covered wood (S&G or strip) kayaks and canoes with 6 oz. fabric and
epoxy of various brands with zero problems. I've used it in multilayer
kayak repairs with zero problems. I suspect that there's more to this
story.