Epoxied Mat over Polyester Hull

[Clivevon]

See also Don Casey on which resin to use - https://www.boatus.com/boattech/case...ster-epoxy.asp

[rbk]

Originally Posted by Cheechako

Poly Laminating Resin has been used for many decades over poly laminated resin. It's more common than epoxy actually. In fact that's how fiberglass boats are built. Sometimes the hulls sit for weeks or months before more components were laminated into them. Repairs are commonly done that way also. No idea where you got that from.

Many many sources and years of laying poly resin. Here’s one of the first links on a simple google search https://www.boatus.com/boattech/case...ster-epoxy.asp

[rbk]

And another...
https://www.epoxyworks.com/index.php...s-boat-repair/

[Cadence]

Originally Posted by expozen

I epoxied some mat over the inside of my hull in a small 1’ x 2’ area. When I was cleaning up the masking, I inadvertently caught the edge of my knife underneath the new mat (between mat and hull) and it started to delaminate from the hull. I used west with fast hardener, 1.5 oz mat, and peel ply over the top. The area is below the waterline and is probably a consistent 50 degrees. It’s been curing for about two days now. The hull surface was preped by removing paint with a wire brush on a drill, than cleaned with acetone, then brushed with a hand wire brush, then cleaned with acetone, then lightly hand sanded with 80 grid, then vacuumed. I have very little experience performing fiberglass work, but I would think that I wouldn’t be able to pull the newly epoxied mat off the hull by just wedging a knife in there. Boats are hard.

JMHO, You totally eliminated any tooth by using a fine grit sandpaper. You should have disked the area with a course grit. Again, JMHO.

[rbk]

Originally Posted by Cadence

JMHO, You totally eliminated any tooth by using a fine grit sandpaper. You should have disked the area with a course grit. Again, JMHO.

80 grit?

[Michael Pope]

Was the boat in the water? if yes. Then it was just too wet!!! Polyester and glass is just slightly hygroscopic (spelling?) it attracts moisture . Wait til you have been out of the water or Hot dry it with a Hairdryer sirst and just before The epoxy iHeat will help the Epoxy to start cooking and use woven material.
Ahmen! Mike Pope

[Happydrv]

Originally Posted by Island Time O25

Asked my boatbuilder buddy about this. He said his first suspicion, if the lay up was done correctly, would be a stale hardener. As in past it's expiration date or not closed tightly enough from even very recent use.

Another example of bad forum advice. This from West System:

I don't know where you got that quote from but hardener will last for years. If left open a long time, it could absorb some moister that could affect the cure. I have added a link to our webpage about shelf life.

https://nam04.safelinks.protection.o...amp;reserved=0

Terry Monville |
Gougeon Brothers, Inc.

[expozen]

Originally Posted by Michael Pope

Was the boat in the water? if yes. Then it was just too wet!!! Polyester and glass is just slightly hygroscopic (spelling?) it attracts moisture . Wait til you have been out of the water or Hot dry it with a Hairdryer sirst and just before The epoxy iHeat will help the Epoxy to start cooking and use woven material.

Yes. The boat is in the water. I’m aware that poly resin is somewhat water permeable but I didn’t think it was to the extent that it would prevent layup while the boat is in the water. Is this true? I find it hard to believe that fiberglass work below the waterline can only be competed during a hall out.

[sand6000]

There have been a few questions asked about what type of "mat" but I did not see an answer. There are Silane binders used with Chopped Strand Mat that make it unsuited for use with epoxy but excellent with polyester. Epoxy should always be used with glass cloth, woven fabrics, exotics etc. Also don't use resin over the top of peel ply. It defeats the purpose.

[rbk]

Unless it’s noticeably wet or has been wet for a long time epoxy will cure and bond (some can do both completely submerged) If it feels damp/clammy I’d dry it out more. A simple test would be to throw some cornstarch on an area. If it stays a powder and doesn’t ball up or wet out it’s fine (give a good clean when done) Poly won’t even cure if water gets involved.

[expozen]

Originally Posted by sand6000

There have been a few questions asked about what type of "mat" but I did not see an answer. There are Silane binders used with Chopped Strand Mat that make it unsuited for use with epoxy but excellent with polyester. Epoxy should always be used with glass cloth, woven fabrics, exotics etc. Also don't use resin over the top of peel ply. It defeats the purpose.

CSM. I suppose mat could be confused with bi-axial mat (which shouldn’t contain binders because it’s stitched together?). Sorry for the confusion. But elsewhere in this thread I mentioned that I did the same work but used two layers of 5.6 oz cloth instead and had the same result. The CSM was most certainly wetted out throughly. So unless the binders effect the chemical reaction of the epoxy I’m unsure if it would effect the bonding. This isn’t a curing issue. The epoxy has cured hard in the time it’s rated for at the specified temp. The issue is the bonding. I guess the best would be to clean the area again, and then sand with a courser grit (36?). Is there a grit that is too rough? I’m hesitant to get too crazy with the sanding because half of the area is exposed roving, and sanding it means possibly sanding into the glass fibers of the roving. Which seems like a bad idea.

[Happydrv]

Sand 6000 was correct. This too from Gougeon Brothers:

Most chopped strand mat (CSM) is not epoxy compatible. CSM has a binding agent holding the strands together and needs styrene to dissolve the binder to wet out properly. Most epoxies including West System are solvent-free.
I added a link to one of our epoxy works articles that you might enjoy.

https://eur04.safelinks.protection.o...amp;reserved=0

Terry Monville |
Gougeon Brothers, Inc.

[Cadence]

Originally Posted by expozen

CSM. I suppose mat could be confused with bi-axial mat (which shouldn’t contain binders because it’s stitched together?). Sorry for the confusion. But elsewhere in this thread I mentioned that I did the same work but used two layers of 5.6 oz cloth instead and had the same result. The CSM was most certainly wetted out throughly. So unless the binders effect the chemical reaction of the epoxy I’m unsure if it would effect the bonding. This isn’t a curing issue. The epoxy has cured hard in the time it’s rated for at the specified temp. The issue is the bonding. I guess the best would be to clean the area again, and then sand with a courser grit (36?). Is there a grit that is too rough? I’m hesitant to get too crazy with the sanding because half of the area is exposed roving, and sanding it means possibly sanding into the glass fibers of the roving. Which seems like a bad idea.

Make sure to hold the disk relatively flat so you don't gouge anything out. Even if the matt was 2oz it's not very thick. There may be some truth to some matt not wanting to except epoxy? It sounds more like a bonding issue than saturation or curing. What about an issue with the temp. of the hull? Good luck.

[contrail]

Originally Posted by expozen

That’s a good idea. I always feel hesitant to do that because I feel like it’s not the responsibility of a vendor to teach me how to fix my boat, especially whenever they have such a breadth of literature available to teach yourself. But I’m feeling pretty stumped on this one.

I have found that most vendors are more than willing to help and many tech departments can tell you lots that is not in the literature. They make the stuff, after all, and their reputation depends upon your results.


However, these days, most folks shy away from the manufacturers, for some reason (fake news conspiracy?) and would much rather use advice from unknown sources on the internet. CF is no exception.

[Cadence]

I went back and read your original post. I'd give you dollars to donuts that that 50 degree hull temp. is the cause of the bonding problem.