Pre-Release / Alligator Problem

Building a box. I am using unwaxed polyester gelcoat. Don't have spray equipment so I am applying the gelcoat with a brush (which is why I need to apply two coats). My mold is made of melamine with clay fillets in the corners and some tuck-tape covered wood. The first application goes on without a problem but when I apply the second coat, major pre-release takes place. It's happened twice now and I don't know what the issue is. The first time, I waited a few hours for the first coat to begin curing before the second coat was applied. After seeing the results (which occur within 20 minutes of applying the second coat) I suspected a hot mix so I corrected for the second attempt by using less catalyst and waited longer for the first coat to cure. Still no success, both attempts failed with almost identical results. Room temperature is a little low, around 13ºC / 15ºC but that's normal for me and I've never had cure problems before. This is becoming an expensive mess. Any suggestions?

 

You need to be in the 70F degree range and wait for the first coat to cure and the second also before laminating. Styrene fumes sink, you need to ventilate the styrene out by have the box on it's side or a good fan. Thin thickness of applied gelcoat doesn't cure well, it's hard to get it right with brushing.

 

Your first layer is undercured, which causes it to "aligator" when the next layer (gelcoat or resin, does not matter) is applied.

So:
-use more catalyst
-heat up the working area
-apply the gelcoat thick enough
-get rid of styrene in the box (will inhibit cure)

 

Thanks. Both of these two suggestions echo the opinions I've gathered elsewhere. The styrene isn't a problem because the box is bottomless (although I do have a fan pointed at the upside down u-shaped flange which would otherwise trap some styrene). I will heat up the working area a few degrees and increase the amount of catalyst. It seems I should have done that on the second attempt instead of going in the opposite direction. Thanks for the advice. Much appreciated.

 

OK, go for it!

Herman

 

pre- release

I will go with Sam Sam on this ,just a note for inside corners you might check out wax fillets from Freeman Supply, work slick.Fritz

 

I am sure you are measuring you catalyst accurately but I'll throw it out there. It should be catalized at 2 to to 2.5% by volume and you should have a gel time around 20 to 30 minutes.

Hopefully you can get your shop warmer I see you are in Canada in the winter pretty cold.

I am sorry to tell you here where I live it was 78 f degress yesterday , stay warm

 

What does "alligator" mean?

 

Its a long green swimmy thing with a big jaw and lots of teeth and a meaty tail with a bad disposition towards humans and probably bad breath as well.

Oh and ps: they growl and hiss as well- bit like my missus now that I come to think of it.

 

Alligator-bite you, when the gel coat is not fully cured and you put the 2nd coat of gel coat over the not totaly set up1st coat, the suface from the 1st coat of gel wrinkels Alligators

 

Alligatoring, partially filled with resin.

 

When the gelcoat is under cured it wrinkles and pulls away from the mold surface. As you can see in Herman's photo, the result looks somewhat like alligator skin.

I've never catalyzed over 2%. Not sure I want to go much higher. Due to the low temperature and, thus, high catalyst ratio and short pot life I am mixing 12oz (350ml) batches. I'm thinking the catalyst should be around 8ml, perhaps I should go as high as 10ml? If I can warm up the space and eliminate some humidity, then 8ml (a hair over 2%) should be more than enough. Right?

 

By the way - thanks for the Southern California Weather Report! I am not at all jealous. Well, maybe a little.

 

....yteah, I am worried about the catalyist ratios too, keep them lower rather than higher, it is after all a catylist, so you do not want any more MEKP floating about in the finished product than necessary anyhow.
I usually go 1.5% max....the factory ratios are usually 1 to 2%.

 

...the catylist is not the cause of the crocodiling (we do not have aligators here)....