Gelcoat Deck Repairs

[oldsaltoz]

Hello everyone,

Again, thanks for the overwhelming quantity of information.

Someone here mentioned that sticking flowcoat (or any polyester) over epoxy will only bond mechanically, which I'm sure is true, but got me thinking: Isn't this true of almost everything I'd apply flow-coat over, and in particular, my original gel coat?

Which then makes me wonder, is there someone that can be done to existent original gel to chemically reactivate it after all these years, and allow the new stuff to chemically bond?

Matt

Hello Matt,
NO, your original gel coat is a polyester, as is the new flow coat, so no problems binding.

The prime reason for gel coat failure is the lack of proper preparation, cleaning just prior to application is important.

Epoxy will stick well to 'almost anything' but almost nothing sticks well to epoxy. Silicon behave in much the same way.

Also worth noting that fibreglass more than 8 weeks old will only mechanically bond and chemically bond, this is the prime reasons epoxy is used in repairs that require high strength chemically and mechanically bonded.

Confirmed this for myself by destroying test pieces a few years ago, reasonable clean separation at the new layup level.

This was not the case with an epoxy resin over polyester, the breaking point was almost double and not at the interface between the two products.

Good luck and fair winds.

 

[ningcompoop]

West carried out testing that indicated polyester gelcoat will bond just as well (i.e. mechanically) to a properly prepared - cured, cleaned and keyed - epoxy surface as it will to a cured polyester surface:
http://www.westsystem.com/ss/polyester-over-epoxy/
I'm sure you can't reactivate a cured polyester surface; any solvent or chemical that softens it will only be causing damage, the curing is not a reversible reaction.
Manufacturers (including Scott Barden) produce polyester gelcoats produced specified to use over epoxy composite constructions, although these are primarily aimed at use in initial construction/lay-up, not repairs, AFAIK.

John

 

[MattA24]

Hello again,

I've ordered a tube of gelcoat filler, some acetone and a tub of flowcoat.

I'm also much obliged to everyone on here to weighed in.

Cheers!