Epoxy over Polyester and vice versa

[rnummi]

What's the scoop on pouring poly over epoxy and vice versa? Any info would be appreciated. Assumption would be the base coat of either/or had fully cured.

[Pitou]

Rule of thumb is: epoxy over polyester, but not polyester over epoxy.

[rnummi]

Ahh, but what happens when you pour poly over epoxy? It just doesn't adhere or is there a more sinister reaction (like when you add nitro and glycerin)

[jleonard]

It won't blow up. It will adhere at least in my experience. I've done it a few times in non critical areas.
I would prefer to do as already stated, apply epoxy over polyester.
But "pouring"? You don't "pour", you apply.

[Pitou]

Poly over Epoxy will not bond or if for some reason it does it will be temporary and fail. Like Jay says, if you use Poly over Epoxy don't "apply" it in any critical areas.

Because of cost savings, Poly is what most builders use. Once you start using Epoxy you need to remember where you use it.

[jleonard]

Poly is what most builders use. Once you start using Epoxy you need to remember where you use it.

That is why my choice for repairs will be polyester resin with only a very few exceptions. Also for those areas where it can apply, bondo is compatible with polyester resin and can be used for small imperfections and to hold panels in place (because it cures quickly) so you can fiberglass over them or tab them in.
And for the same reason, it is preferable to paint over epoxy, rather than gelcoat.

[rnummi]

so in my case, the fact that the sides of the pilothouse are essentially solid cured epoxy should not impact a polyester resin pour across the front (essentially) two solid vertical side surfaces of epoxy meeting the solid polyester vertical of the front. It will save a ton of $ (even using raka). I'm estimating 3 gallons of resin to fill the front.

What I end up with is a solid pilothouse that will never "delaminate" or rot ever again. I'm not particularly worried about non-adherence of the two as the gap (if any) will allow moisture drainage if that ever happens.

[jleonard]

If you are using resin as "paint" it likely won't adhere well in the long run in my experience. That sounds like a poor attempt at a repair to me.

[rnummi]

I'm not using it as paint. I'm filling a six inch void (that was rotted away) on front base of pilot house. Core is non existent so was going to do a 2-3 inch base of epoxy then fill remainder w poly.

[jleonard]

Without any material such as mat or cloth? Just resin?

[rnummi]

Decided to go w straight epoxy.....dollar for dollar I'm slowly building a Hinckley (w resale value of a 77 Chevy Vega)...

[Beta Don]

.....dollar for dollar I'm slowly building a Hinckley (w resale value of a 77 Chevy Vega)...

I own one of those!! . . . . with about 5 gallons of epoxy on it too!

IMO, epoxy is the only resin to use when repairing fiberglass boats - It bonds to old polyester lay-ups much better than a coat of new poly does. When a polyester boat bottom develops a cars of the blisters (seawater penetrating the gel coat interacts with the chemicals in the polyester and forms a 'pus' which delaminates the lay-up) the only 'cure' is to grind out all of the cancer and replace it with layers of glass and epoxy. To prevent the 'pox' from happening in the first place, there are several epoxy based products which you paint over the gel coat to seal it - Interlux 2000 is the most popular one. My boat has 4 coats of 2000 over the repaired hull. Boats built completely from epoxy seldom develop the pox because epoxy is much more waterproof than poly

Don

[Sprig1]

Don I was just going to ask that question about barrier coating and what everyone thought. My hull is perfect on the outside right now. Very little build up someone must of scrapped it. I will probably get it in the water then do it some other year. I have enough projects. But want to hear your opinion and others

[Beta Don]

If your hull is perfect and has never had a blister problem, you're probably not going to develop one anytime soon. My hull had no signs of a blister problem either when I bought it, but when I took it down to bare gel coat I could see that it had indeed suffered from the pox at some time in the past and someone had done an excellent job of properly repairing it. Knowing that the problem is worst in warm waters and not wanting to have it return, I opted for the Interlux 2000 treatment prior to doing the bottom job - I had already sanded it bare, so it was the prefect time to do it

When you do the bottom paint on top of the epoxy, 2 quarts will roll on a light coat of contrasting color bottom paint (red if you're going with blue bottom paint) and that way you can tell when your bottom paint is about worn away - Your hull will start to change color. We got 2 heavy coats applied using 6 quarts of Micron CSC

Don

[Pitou]

I was just going to ask that question about barrier coating and what everyone thought. My hull is perfect on the outside right now. Very little build up someone must of scrapped it. I will probably get it in the water then do it some other year. I have enough projects. But want to hear your opinion and others

I also had taken on the Interprotect barrier coat project with my 28. I'm grateful that it has already been done on my 31. If you're taking her down to the gel coat, why not, but it sure is a big roll up your sleeves project! Here is a link from beginning to end:

viewtopic.php?f=7&t=3987