How to make polyester waterproof

[Yane]

Hi, due to number of reasons I made 10 foot fishing boat from polyester and plywood with inside ribs made of pinewood. Since polyester is not waterproof (and there is some blisters) I was thinking to coated it with marine lacquer or exterior oil paint to sill all pores, may be even some spraying filler prior painting. So I'll be glade to know your opinion about this idea.
Greetings from Macedonia

[lewisboats]

Sand it well and give it a coat of epoxy if you can...if not then a couple of coats of primer and a good painting will be as good as anything.

[gonzo]

Are the blisters on the gelcoat or between the fiberglass and the wood?

[Yane]

Most of the blisters are between coats of fiberglass (I put two layers) and some are on pinewood (ribs, rails on bottom and bumpers on the bottom and top)

[Yane]

Originally Posted by lewisboats

Sand it well and give it a coat of epoxy if you can...if not then a couple of coats of primer and a good painting will be as good as anything.

What kind of primer do I need (pls specify the type not the brand) ?

[gonzo]

From your description, it is a failed laminate. I don't think it has nothing to do with waterproofing. Polyester does not absorb more water than wood. The only proper fix is to grind the laminate and redo it.

[Yane]

Originally Posted by gonzo

From your description, it is a failed laminate. I don't think it has nothing to do with waterproofing. Polyester does not absorb more water than wood. The only proper fix is to grind the laminate and redo it.

ok, I'll do blisters (I'm still in phase of building it) but how to sill pores in polyester sheeting to stop osmosis

[lewisboats]

I use Rustoleum Marine Primer.

[gonzo]

Are you having blisters before you finished building it?

[PAR]

Those aren't blisters as we know them, which is the result of a chemical reaction between water and the by products of the polyester cure process. What you have are dry spots and incomplete wetout areas. These are usually caused by air bubbles in the lamination process, typically trapped between fabric layers or under the laminate between the substrate and the fabric.

The only repair for this is to grind out the affected areas, then fill with more polyester or better yet, epoxy. To water proof the polyester, you need a barrier coat of epoxy. No primer, just sand the whole surface with 100 - 120 grit, then roll on some straight laminating epoxy. Two coats minimum and tip it off for a good finish. Now the surface is waterproof and ready for fairing and eventually primer.

[Yane]

Originally Posted by PAR

Those aren't blisters as we know them, which is the result of a chemical reaction between water and the by products of the polyester cure process. What you have are dry spots and incomplete wetout areas. These are usually caused by air bubbles in the lamination process, typically trapped between fabric layers or under the laminate between the substrate and the fabric.

The only repair for this is to grind out the affected areas, then fill with more polyester or better yet, epoxy. To water proof the polyester, you need a barrier coat of epoxy. No primer, just sand the whole surface with 100 - 120 grit, then roll on some straight laminating epoxy. Two coats minimum and tip it off for a good finish. Now the surface is waterproof and ready for fairing and eventually primer.

Thank you for this advise I'll do that, and you are right I have air trap in between fiberglass layers, not blisters like you explain, I'll grind down that area and put new fiberglass layer

[ondarvr]

Also, since this is a small boat and probably doesn't spend a great deal of time in the water, the fact that Polyester isn't as water resistant as epoxy will have little effect on how well holds up. It will have more to do with how good of a job you do in the details of building it.

[Yane]

All I'm afraid is rotting and splinting of plywood. Wood work is relay good. So now I'm trying to seal pores in fiberglass and not to spend so much money on sealing material

[PAR]

Ondarvr, I have to disagree with the idea that polyester will have little effect on durability. Considering the current issues, I suspect not full encapsulation of the wooden elements, so there's going to be environment changes, placing strains on the sheathings and coatings, which will eventually fail as a result.

[ondarvr]

I am referring to the fact that he has what may be air voids and other defects in the laminate, this is far more of a concern than the type of resin used on what he wants to be a low cost boat. If there are dry spots or gaps where water can get to the wood the type of resin is irrelevant, it will rot with either one and just coating it with epoxy (which would have been better and cheaper if it only needed to be done once) may not be enough to prevent water intrusion at this point. If he repairs the voids and/or dry spots with polyester which he may already have on hand, it should last at least a good amount of time with a little care.

I’m not saying there is no difference between the two products, only that considering his original objective and at this point in the construction process, switching products may not add to the life of the boat as much as paying attention the details.