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Old 25-10-2011, 14:22   #1
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Forgot Hardener in the Gelcoat

OK. I feel like an idiot.

I've been working on the boat like crazy - so much to do before she goes in the water in 5 days (yay!) and this morning I spent a long time delicately adding the tiniest amounts of tint to the white gelcoat to colour match it to my boat. When it was just right, I went around and painted the areas that needed to be painted (quite a bit)... and then did it again with a second coat.

It was then - when I came back to where I had mixed it - that I saw my FULL bottle of hardener. Darn!

It certainly dried/hardened a bit between coats... and it IS very hot in Mexico. I know that polyester resin eventually hardens with out catalyst in the heat... anyone know if this gelcoat will do the same?

If it is epoxy based than I think it will NOT harden. If it is polyester based I think that it MIGHT harden on it's own.

It is the kind of gelcoat that does not need to be cured with plastic over it (I guess it has wax in it?)

Anyone know what I should do? Scrape it off and do it again?

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Old 25-10-2011, 15:09   #2
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No, you're not the first.

Once, in our business a very large job (40 gallons) was completed before we realized that someone a the factory had filled the hardener containers with resin (they blamed it on a disgruntled employee).

Get started stripping. The longer you wait the more difficult it will get. Scrub off with with solvent and scratch sand. Swearing helps.

Since then we ALWAYS do a small test pot before starting with a new batch or a new-to-us product.

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Old 25-10-2011, 15:21   #3
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Re: Forgot hardner in the gelcoat

Yes, it will harden eventually, but you probably won't still be around when it does. The catalyst's (hardener) job is to speed up a naturally occurring process by many orders of magnitude. In this case, several decades.

Sorry, but you will need to remove it all and do it over.


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Old 25-10-2011, 15:23   #4
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Re: Forgot hardner in the gelcoat

To paraphrase Homer Simpson "DOH"! How much acetone have you got?
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Old 25-10-2011, 16:04   #5
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Re: Forgot hardner in the gelcoat

A friend of mine did a whole 15 foot dinghy with red 2 part. But forgot the second part.

Took a whole lot more work to strip it off.
Bill Streep
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Old 25-10-2011, 16:08   #6
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Re: Forgot Hardener in the Gelcoat

I once did the same thing but got the two different sized cans of epoxy hardener and mixed the two together. You guessed it. Hardener never dries!

What a mess to clean up.

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Old 27-10-2011, 01:58   #7
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Re: Forgot Hardener in the Gelcoat

It will harden, but the reason it will harden is that it will "dry", as opposed to "chemically cure".

So even if it looks "dry" go crazy with acetone and wipe down.

Go to FMS (now Valspar composites) - they sell acetone in 16L drums and it's WAAAY cheaper than buying 4L cans from Bunnings etc.

Get some white rags and go crazy, changing rags often.

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