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CarolinaMarshWalker

What caused gel coat to lift from mold?

7 posts in this topic

Making a part on a male mold.  I've made several of these parts with no problems.  But, the most recent part did something weird.

 

Mold was prepped with 10 coats of mold release wax.

Temperature was in the mid 80s (F).

Humidity was in the low 80s (F).

 

Sprayed the mold with typical polyester gel coat catalyzed at about 1.25%.

The gel coat setup rather quickly, but, nicely.

 

About 2 hours later, I applied the skin coat of 1.5oz chopped strand matt.  During rolling that layer, noticed a bulge rise in the gel coat about 2" x 1.5" and about 1/4" deep (off of the mold).  I was initially afraid the mold was delaminating.  The bump stopped growing, so continued layup.  Once the part was set, popped it off of the mold without any problem and the part looks fine except the bump.  Even the surface of the part inside the bulge where the gel coat lifted away from the mold looked consistent with the rest of the part.  The mold looks fine.

 

What could cause the gel coat to release from the mold and bulge away from it? 

Can applying the skin coat to soon cause that?  To much styrene from the skin coat softening the gel coat? 

 

I don't think there was any moisture/water on the mold, but, can moisture or water on the mold cause this?  Or, other contaminant?

 

I realize this may be hard to diagnose over the interwebs, but, just looking for possible causes.

 

Thanks.

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Looking at the catalyst chart, at 79 - 80 degrees it shows 1/2% catalyst.  It could be that the gel coat set up too fast using 1.25% at that temperature.

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Similar thing happened to me. I waxed and sprayed 2 coats of PVA into a simple shaped aluminum mold. Brushed on 2 coats of TotalBoat non-waxed laminating gelcoat with black pigment and 2 hours later gelcoat was separating from mold. (see pics.) Ambient 65 deg F, 59% humidity, indoors. Mix was 4 oz gelcoat, 45 drops MEK, teaspoon (or less) of pigment. What happened??

Surf

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Okay, here is an update. I thought if I finished the layup I might flatten the gelcoat bubbles out with the ribbed roller. No such luck. I laid on 3 layers of 1.5 oz CSM and TotalBoat laminating resin and rolled all the bubbles out of the layup. When I de-molded this morning this is what I found: The PVA film worked beautifully, I thought the PVA might be sepearting from the mold, but that was not the case. It was 100% the gelcoat wrinkling and blistering in the mold, some places as much as 1/8 inch! The gelcoat cured hard as a rock as it should. The spaces between the wrinkles look exactly like what I was shooting for. The PVA peeled of in nice sheets and the CSM/Polyester resin layup turned out fine. What went wrong with the gelcoat???

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That usually happens if the gel-coat is over catalyzed causing it to harden up too fast and pull away from the mold and pucker.  Next time try about 35 drops for 65 degrees.

 

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32 minutes ago, RickW said:

That usually happens if the gel-coat is over catalyzed causing it to harden up too fast and pull away from the mold and pucker.  Next time try about 35 drops for 65 degrees.

 

Thanks Rick: In your reply to the first post in this thread, you refer to a catalyst chart. Where might we find this chart for your various resins and gelcoats?

Tom

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