Epoxy vs Polyester or Vinylester Resin

[roverhi]

I"ve removed/changed the location of bulkheads that were bonded to the hull with Polyester Resin. On one boat that had been molded less than 6 months before, the bonded area had been ground with a grinder and wiped down thoroughly with Acetone before the bulkhead was tabbed on. In short, know it was done right in the first place to relatively fresh laminate. When I ripped out the bulkhead(s), found the best way to do it was just to muscle it back and forth till the the tabbing with the hull broke loose. Some bonds did have to be cut/ground off but it was a very low percentage of the bonds. On my current boat with bonds that were done by the factory 40 years ago. It was pretty much the same thing, just rip the tabbing off the hull. Doesn't give me a lot of faith in repairs made with polyester resin.

I don't see where using epoxy resin vice polyester is going to create a stress riser. The strength in FRP construction comes from the fiberglass strands in the matt, cloth, and roving. The resin basically just keeps the strands in place. A bond that doesn't hold well is a hell of a lot more of a problem than a join that may or may not be stronger than the surrounding structure.

[capttman]

Originally Posted by ssanzone

where does your question come from?

do you have an objection?

is there some other element to your post?

personally, i use epoxy when the surface is not as pristine as i might otherwise like it, for structural (tabbing in bulkheads / chain plates beds) items and if i cant tell what the original resin was because epoxy just bonds with everything and is bullet proof.

if i am laying up multiple layers of new cloth on a well prepared surface, i use laminating resin mostly because it is a lot cheaper.

-steve

My question comes out of curiosity. After building several boats including my current one I have formed an opinion. It's based in fact and experience and differs from many here who have done small repairs. So my intellectual curiosity wants to know how others think and why!

[captain58sailin]

Epoxy has a much better resilience than polyester, I cannot speak to vinyl ester, if I had the resources, I would use systems 3 epoxy to built a vessel. Or go with epoxy encapsulated wood. Done right it is hard to beat, on the weight / strength ratio.

[minaret]

[donradcliffe]

I was messing around with the Merlin this week, and have a new data point. Bill Lee had the same question, so he had 6 2x3 in L-shaped pieces of fiberglass fabricated, prepped the inside of the 40 year old hull, and bonded 3 of the pieces with West system and 3 with vinylester.

He drilled a hole in the perpendicular side of the L hooked up a come-along with a load cell, and ripped them off perpendicular to the hull (kind of a peeling process).

Bottom line? The vinylester bond was about 50% stronger than the epoxy.

[Jim Cate]

Originally Posted by donradcliffe

I was messing around with the Merlin this week, and have a new data point. Bill Lee had the same question, so he had 6 2x3 in L-shaped pieces of fiberglass fabricated, prepped the inside of the 40 year old hull, and bonded 3 of the pieces with West system and 3 with vinylester.

He drilled a hole in the perpendicular side of the L hooked up a come-along with a load cell, and ripped them off perpendicular to the hull (kind of a peeling process).

Bottom line? The vinylester bond was about 50% stronger than the epoxy.

Now that is practical engineering! Bill Lee has always been a hero of mine, and I was so happy when he bought Merlin back. I'm envious if you are involved with his new program.

And I have no idea why he got the results that he did, but I'm fascinated!

Jim