Epoxy Repair

[Marv Irwin]

Greetings to the collective,

The ice finally went out yesterday here in northern Ontario and with temperatures close to 75, I tackled the first step in repairing an over-canvassed misadventure of last year. (I blew a come about and went prow first into a very rocky shore....several times.) The damage was relatively minor. A silver dollar sized piece of gelcote missing (down to fibre) right on the prow at the waterline and a few radiating cracks from the impact site. I dremmeled the edges, removed loose stuff and feathered out the star crazing. After a good wipe down with acetone, I placed a fist coat of a product called "FLEX SET" which is supposed to be non-sag epoxy that resists vibration, bending and shock.
Here is my question: This is my first time working with epoxy. Should I aggressively sand to basic contour so there is a good "tooth" on the repair surface for a second coat, or should I apply a second coat directly over the first with no sanding? This material comes with tons of instructions (including a prominent warning that "this product contains a chemical known to the State of California to cause cancer"), however no directions about the second coat.
As always, all help is appreciated.

Regards,
Marv

[algonquin]

I have seen it done both ways but my personal preference would be to scuff the first coat then apply the second. Brad

[Phill]

My experience with Epoxy, System Three brand, is that it will chemically bond to a previous coat without any further preperation.

Try to find a website for the product you are using. Perhaps the site may even have a FAQ page or a Contact Us for questions.

When repairing with resins remember:
Polyester to base polyester. OK..... what all our DS's are made of.
Epoxy to base polyester. OK
Epoxy to base Epoxy. OK
Polyester to base Epoxy .... will not work.

So whenever repairing with epoxy, remember where you use it and make sure to use only epoxy on that area thereafter.

Another caution about Silicones, like the polishes many of us use.
NOTHING will bond or stick to an area with this stuff on it. And when used the silicone molecules migrate to 'pollute' nearby areas also.
Found this out from guitar repair sites. Those who repair guitars, etc... really hate the silicones. No glue, resin, superglue (C A) or other bonding agent will work, without removing contaminated material. They say no safe solvent will clean it off.

When sanding and feathering for a repair, we are probably getting to clean material for bonding. Just an FYI about Silicone. ( it does explain some failed repairs on my boat though )

phill

Polyester or epoxy for repair ?? maybe another thread for discussion.

[Roger]

The only other piece of advice missing to the excellent suggestions provided have to do with a curing artifact of epoxy. as it cures an amine blush may rise to the surface. This will prevent a second coat from adhering well, so wipe it off, preferably with acetone, which will also slightly soften but really clean the surface of impurities, so that a second layer adheres well. The typical trick with a second coat is to apply it when the first coat is green, that is when it has just cured to the point that you can still make an indentation/scratch with your fingernail but not glass hard. After that you need to give it an acetone wash, and let it dry before the second coat. You can also give it a light tooth with say 120 wet sandpaper if it has cured more than 4 days, (full cure).

This is not the case with polyester resin, only epoxy.

Hope that helps.

[GreenLake]

System three makes some epoxies that they claim don't have any amine blush. In their silvertip line.