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Author Topic:   Gelcoat Won't Harden
Sinclair7 posted 08-12-2001 07:04 PM ET (US)   Profile for Sinclair7   Send Email to Sinclair7  
I recently did some gelcoat repairs on my 13. I did not color some because they were covered with bottom paint and these hardened really well. Where the gelcoat was colored, it will not harden. Now I'll have scrape off the partially hardened gelcoat and start over. Any advise on why this happened and what to do about it would be really appreciated.
kingfish posted 08-12-2001 09:46 PM ET (US)     Profile for kingfish  Send Email to kingfish     
My experience has been that all gelcoat I've had access to (with the exception of Spectrum's *paste* gelcoat - in 2 oz. jars) has required a release agent to be sprayed on the gelcoat immediately upon application in order to cure properly. No release agent, no cure.


LarrySherman posted 08-12-2001 10:10 PM ET (US)     Profile for LarrySherman  Send Email to LarrySherman     
Correct, check jimH's article on this subject in the repair section. Great info to be had in it.
jimh posted 08-13-2001 09:02 AM ET (US)     Profile for jimh  Send Email to jimh     
Not hardening when exposed to air is a property of gelcoat. You have to cover it up to get it to harden.

You can spray it with Polyvinyl Alcohol (PVA), or you can cover it with a sheet of platic wrap.

Also, introducing the tinting agent may have affected the catalyzation. Perhaps you needed a little more catalyst.

One interesting difference between epoxy and polyester resins like gelcoat:

With epoxy you are supplying two different sets of molecules (the resin and the hardener) which will chemically link up and bond. Therefore it is very important to mix them in the exact ratios, otherwise you'll have some of one type of molecule left over and not bonded to anything, making the batch weaker.

With resin, the stuff is all set to harden, it is just waiting for the catalyst to start the reaction. Once started, it is a matter of time, temperature, and reaction rate before it cures. Apparently the presence of air inhibits curing to a hard surface.

When making boats in female molds, the gelcoat goes in first and thus cures to hardness because it is later covered with more material. In fact, this is an advantage because you want the follow-up layers to form a primary bond to the gelcoat layer. So the laminate layers are added as the gelcoat is curing, and they all cure together with primary bonds.

Epoxy is a stronger adhesive and can produce stronger secondary bonds than polyester resins, so for making repairs is produces better bonding.

The knock on epoxy (besides the higher cost) is that some people have trouble topcoating epoxy with gelcoat. That is caused by failure to remove the amine blush on the cured epoxy, which can only be removed by hard scrubbing with soap and water. Solvents like acetone will not remove amine.

I have the repair-with-epoxy trick down pretty well, but I am still learning about topcoating with gelcoat and getting a good match. There are some holes on the transom that will be my next spot for experimentation.


Wild Turkey posted 08-13-2001 09:38 AM ET (US)     Profile for Wild Turkey  Send Email to Wild Turkey     
Are you using Spectrum Gelcoat paste? In my experience with this product, if too much catalyst is added it will not harden properly. I think Tom W. Clark has mentioned this happening also.
Also, I don't think Spectrum requires PVA for proper curing.
bigz posted 08-13-2001 10:33 AM ET (US)     Profile for bigz    
Didn't flash off on some but the other areas did!

These areas which didn't flash was it a newly mixed batch or did you use the same batch as the others which flashed?

Did you have a surface additive (wax) added which wouldn't need a spray over of PVA?

As JimH mentioned did you fill the gouge with epoxy or were you just filling "spider" cracks, surface overcoat with gelcoat?

Did you de-wax the area your repairing in other words clean it thoroughly to remove any old wax or polish using acetone or fact similar?

Lots of reasons for gelcoat aside from improper mixing not to flash off. So give us a tad more information if you would.


andygere posted 08-13-2001 01:11 PM ET (US)     Profile for andygere  Send Email to andygere     
A company called MAS makes epoxy that does not produce amine blush. I used it to build my sea kayak, and it is as good or better than West System. I have used it for filling holes, etc. with great results.
Sinclair7 posted 08-13-2001 09:29 PM ET (US)     Profile for Sinclair7  Send Email to Sinclair7     
I used "evercoat" polyester gel-paste. I bought a new can and started new. This batch seems to have hardened well with the coloring agent. The can does not mention PVA. It only states, "for greater smoothness and higher gloss, this repair should be covered with a piece of clear plastic release film, like acetate film or wax paper, and left to cure."
I don't know what acetate film is so I tried the wax paper. It cured to the gel paste and had to be sanded off.
I repaired a few dozen old screw holes where the old rub rail was attached and used the gel-paste to cover the epoxy. The epoxy worked really well. Hopefully, the amine blush won't be a problem because I sanded all the dried epoxy, to shape it. Also, there were some pretty deep chips which I filled with epoxy and sanded smooth. If I seem to be doing this all wrong, please let me know. This is my first boat and I only know what any of this stuff is by reading the postings.
Where is PVA sold? I don't think I saw it at the boat store.
LarrySherman posted 08-13-2001 09:59 PM ET (US)     Profile for LarrySherman  Send Email to LarrySherman     
You are doing fine.

You can find PVA at West Marine or Boat US, just look through all the stuff in the paint and fibreglass section. The sales staff most likely won't know what it is. It just comes from headquarters automatically.

If you changed sand paper frequently while sanding the epoxy, you are proably ok on your gelcoat over epoxy repair. What happens in the worst cases is that the amine just gets smeared around the repair by sanding, and is still there even after wiping with acetone. You are most likely ok. I'd just wait and see.

It sounds like you are doing some great work, good luck!

bigz posted 08-14-2001 08:20 AM ET (US)     Profile for bigz    

Heh heh that clinging plastic wrap from the supermarket can be used as the "clear plastic release" stuff just so you know for future reference.

The one thing I see is that using gelcoat paste isn't necessary. This product is designed to actually fill small cracks and dings in itself. Since your using epoxy then gelcoating, using just gelcoat either brushed on or sprayed on is all that is necessary over the epoxy fill and fairing.

Since the Evercoat gel paste as mentioned could be used to fill small areas by itself without the need to use epoxy, use it if you have any other areas your doing which aren't deep gouges. Anyway, since you have it go ahead and keep using it as your gel top coat just a little more work.

Follow JimH's recommendation to thoroughly soap and water wash the epoxy areas before using the gel paste.

Sounds like your having fun, want more info purchase that West manual on repairs explains it pretty straight forward with out getting to technical.

Andy I whole heartly agree, the MAS system is excellent have used it with great results. They are located about 20 miles form our boats so I buy it direct since our marina only carries West and the other "body" filler gel and epoxy products, the folks have been super helpful if you do run into a technical problem. Tom

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