Polyester over epoxy primer pin holes.

[EX Wanabe]

I am trying to repair the damage done by a painting crew who used grinders to remove the gel coat on a catamaran creating extensive damage to the hull. It is an older catamaran made with polyester.

I filled the ground through areas with polyester mat. I then reglassed the bottom with cloth to strengthen the hull seams with polyester. I did not apply cloth to the sides. I then sprayed it with Comex Epoxy Primer for a barrier coat.

The bottom is fine where I applied the cloth, but on the sides of the bottom where there is no cloth, small pin holes appeared that can not be filled with epoxy primer by spraying. They could be filled/covered with a roller, but my friend wants it sprayed as Comex suggests.

I know that you can not put polyester resin over epoxy resin. My question is;
Can I apply polyester resin mixed with talc to fill these pin holes.

[tronic72]

There's a guy on YouTube whose business is Boat Works Today. He does lots of really handy HowTo videos.

In one of his videos he tests the "myth" or rule that poly won't go over epoxy. The results are surprising and he found that contrary to popular wisdom, poly does stick to epoxy.

Here's the link. https://youtu.be/kHAbyglpp3M

Hope this proves useful.

[Zach]

If it isn't a gel coat blister job, you ought to be OK.

If it was a gel coat blister job... I'll throw out a comment that nobody with a blister job wants to hear... Namely fiberglass boats dissolve in water.

Until you have the full build of whatever product you are applying, over the top of the last coat that had pin holes, you don't have a barrier coat. The pin holes are the top opening to air voids in the laminate.

Each of the pin holes is a street address for the next batch of blisters. Not quite to the extent that "it doesn't matter what you fill the pin holes with..." but pretty close.

The epoxy paint and primer is a different breed than laminating resin mixed with filler, as the filler we mix into the resin clumps together and doesn't fully wet out giving a water track through the pin hole along the filler. That is why filler gets soft in water if it doesn't have a lot of resin rolled over the top of it to give it a barrier. Barrier coats designed to be barrier coats, are loaded with ground up minerals that aren't soluable in water. The way they work, isn't necessarily that they are just epoxy... But that they provide a barrier that sea water doesn't try to dissolve and a fine enough fully wet out mix that there are not pathways for water to track through it.

Pin holes defeat that.

If you have a billion pinholes and you are on your first coat, it may well be worth your time to sand off what you have and resin coat the boat twice or three times in epoxy, before starting your barrier coating work and get clear of your pin holes once and for all.

Otherwise if you have a thin coat on top of your pin holes, and put another gallon or two of primer on... you have a 5-7 year timeline and then will be redoing the whole job.

Boats that have a very porous skin layer of mat on the outside, tend to have 2-3 blister jobs done before someone decides to either lay up a few layers of cloth over the outside of the hull and just be done with it... Or do an over the top barrier job that puts 6-8 gallons on where 4 was called for.

The fact that you have voids in the laminate just means that the vapor pressure will find them, if you don't have enough epoxy over the outside to make an epoxy boat around the polyester one.

Zach

[EX Wanabe]

Thank you for the info. I will check out the video. Also regarding the stripping of the epoxy primer, there is no way I can see to strip the primer from inside the pinholes. That is the reason I was concerned about putting polyester resin over the epoxy primer inside the holes. My plan is to mix resin with talc to fill the pin holes, sand off excess and apply the barrier coat.
Thanks again for hour responses.