West System Expoxy Surface Prep-Clean Enough

Schuey

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I'm getting ready to apply a patch over the attached crack. Eventually this will be covered by a (sealed with Lexel) bulkhead.
Obviously I want the patch to stick. The problem is the residue left over from the foam bulkhead. The edges were sealed with some sort of goop(I hope it's gone) but they look like they were held in place with resin as well. The grey stuff is the residual foam stuck to in.

I can keep sanding it off but the concern is going through the original resin and fluffing up the kevlar.

When is good enough? I suppose something like this can't be too clean. I guess I'm wondering just how sticky will the West epoxy be?

Thanks as ever.
 

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JohnAbercrombie

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I can keep sanding it off but the concern is going through the original resin and fluffing up the kevlar.
I wouldn't be concerned if I did that, if I'd planned to cover the area with epoxy and glass. In fact that would probably be my goal.
When is good enough? I suppose something like this can't be too clean. I guess I'm wondering just how sticky will the West epoxy be?
Usually I try to remove old sealant with a combination of scraping and chemicals. If I think there's any chance that silicone was used in the area I use a silicone remover (from an auto body supply shop) after I've scraped the area clean. The usual solvents like acetone and alcohol can be useful. If there's been contact cement or rubbery sealants in the area, contact cement cleaner is usefu. Be careful to get good ventilation going if you are sticking your head into an enclosed space with solvents - a respirator would be a good idea, though I don't follow my own advice on that sometimes.
I've learned (through mistakes) that sanding contaminants into the surface is a bad idea, so I try to get everything as clean as possible before sanding/grinding.

Epoxy is quite 'particular' about adhesion, in my experience. I've had glass tabs (for shock cord hold-downs) pop off the cockpit sole and bulkheads when I haven't done enough good surface prep. I think that there are sometimes residual contaminants from the original molding of the hull?

A sharp scraper (paint scraper style with a handle, not cabinet scraper) is handy for this work. If you are using a steel scraper, you can round off the corners to prevent digging in too far. With a (far better) carbide scraper, I just have to be a bit more 'aware' of what the corners of the scraper are doing.

carbide scrapers.jpg
 
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Schuey

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I never thought of contact cement. That sounds like a good fit. Especially in this application.

The stuff is hard as rock. The Acetone doesn't effect it at all.

Thank you John. Much appreciated.
 

JohnAbercrombie

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The stuff is hard as rock. The Acetone doesn't effect it at all.
Hard lumps are easier to scrape; it's the rubbery stuff that can be vexing for me.
As you said it could be cured resin of some type - it's always interesting to do the 'autopsy' to try to figure out all the stuff that's been put on. over the years, to 'fix' leaks and other problems . :)
 
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