epoxi over polyester

[tropicalbuilder]

how long should be waited before applying epoxi over a new polyester lamination?

[Submarine Tom]

It depends on many factors.

What are your?

-Tom

[PAR]

I think this is a double post, Tom. At least I've answered the exact same question in the last few days anyway.

[tropicalbuilder]

it's a molded hatch base that goes on deck where a bulkhead is taped to the hull.
The molding is iso polyester resin, and the bulkhead is taped to the hull with epoxi and dbm.
If the same question has been answered ... can you tell me where to go and check?
thanks

[PAR]

Apply epoxy over polyester as soon as you can put a good scratch (tooth) into it, so a mechanical bond can be effective. Sorry, I thought this was a double posting. So, the answer is, as soon as you can get an aggressive grit to leave solid marks, on the polyester surface.

[tropicalbuilder]

ok thanks .. my concer was about some kind of styrene release during the curing stage of pe that could affect the epoxi , but if not, i'll just wait a couple of days to make sure and then go on with the epoxi...thanks

[mastcolin]

I would suggest leaving the polyester for longer than fully cured. (for overcoating with paint epoxy the recommendation from International Paint was 3 weeks. This recommendation came via the resin suppliers to Sunseeker and other major builders in UK).

The worry is uncured styrene in the laminate. You need time for this to diffuse out/react.

PAR was right. There are many factors (type of resin, type of lay-up, speed of cure, thickness of lay-up, conditions during cure etc, etc) - and to reduce effects of these to minimal, wait as long as possible. I repeat, for paint, the resin suppliers recommendation was 3weeks. (and paint adhesion properties are certainly no poorer than resin)

Before you do scratch up the laminate, make sure you 1st clean any residual wax/release-agents off before sanding. ie clean it even if you don't SEE anything. If not, you can sand all the contamination into the scratch-marks and the coating can still want to fall off.

[PAR]

Yep, paint formulators will cover their butts with a 3 week cure "clause". They need this level of butt covering, because their products are very sensitive. Straight epoxy doesn't really care. Even if there was some out gassing, it would hurt anything.

Always assume you have an amine blush, even on non-blushing formulations. Non-blush epoxy is mis-labled. It's actually "less likely to blush epoxy" or "maybe it will not blush epoxy". Unless you have complete control over environmental conditions, where you can insure the glycol groups will not leave unreacted amines on the surface, then always assume you have some (because you will). The first time you apply paint, just to have it lift off in huge, $300+ per gallon sheets of unstuck, fully cured waste stuff, all because the label on the goo can said non-blushing formula, you'll learn to always assume you have a blush.

[Herman]

For the same reason the paint pot said "only works on a clean, and degreased surface". So the person who smacked some paint on a non-cleaned epoxy surface (or whatever surface) missed 2 labels (and probably a lot of experience, but that is what he/she is gaining fast then...)

[PAR]

Yep, nothing teaches faster then a surface full of fish eyes with $300 a gallon paint . . .

[Fanie]

I'm curious, why would anyone want to layup epoxy over polyester ? The logical thing to do would be to use polyester on the uncured polyester to get a much better bond than you can get from laying up epoxy over cured polyester. Yes I did test it.

[PAR]

Agreed, a chemical bond with polyester is the choice if you have the option and given it's strength limitations, but in repairs or laminates that have cured, you're better with an epoxy bond then a mechanical polyester bond. In Fanie's case, he's a closet styrene sniffer and purely in it for the buzz, so his reply will always be aligned with using polyester. His cloths are polyester too, as is his inflatable lover . . .

[Fanie]

In Fanie's case, he's a closet styrene sniffer

Almost came true too. I did a bunch of small layups here and put the roller in a plastic bag in the freezer so I can re-use the same over and over.

Only two things was wrong.
1-I didn't seal the bag it was going in
2-I forgot about the roller in the freezer

Soooooo guess what happened. Polyester flavoured meat, Polyester flavoured butter, Polyester flavoured bread... in fact, everything in the figgin freezer was Polyester flavoured.

Had to throw everything away, it tastes disgusting.

The used term 'In the ****' (with the old witch), that was me.

[Herman]

don't mix chemicals with food, you *****. You deserve positive feedback for doing something that foolish, and entertain us with it.

[Fanie]

It was meant to entertain you *****