pillowing effect on my molds

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#1

I have a pillowing effect on my molds when I pop the plug out of it. It has done 2 in a row, different parts though. Both plugs were fiberglass. Could it have been because they got to hot. Our shop thermostat is peged on 85 degrees but it can’t go any higher. we laid 4 layers in one shot. So I am hoping it is because of the heat. When we pop the plug off the plug does not have this effect on it. Also we left the plug in the mold for 5 days before we popped it out and the other for 2 days before we popped it. Please help!

#2

Also we used general purpose poly with 2oz csm. Tooling gelcoat was the surface

#3

I’m sure you know about the “green” stage in the curing process?

Lay-up a layer, wait for “green”, lay-up, wait etc…

That will cure your heat issue, if that is what it is.

More time consuming but it’s worth the wait.

#4

I was thinking doing 2 layers at a time. we did a 1.5 catalyst mix.

But was it the heat that caused this is my main question. I don’t want to make another mold till I figure what caused the problem in the first place. Also keep in mind this mold is 4ftx4ft. So it is a pretty good sized mold. I think the size and the heat it gave off as a whole could have been a big factor

#5

also could this possibly be sanded out?

#6

4 layers of 2oz CSM directly on top of the gel? Did you put down a stabilizing layer first? Your backup layers could have distorted the gelcoat during curing from shrinkage. When I build a mold, I lay the gelcoat and put down a stabilizing layer of 3/4oz mat after the gel sets up. After the stabilizing layer cures, I start buildup with 1.5oz mat. I build up 2 plies at a time allowing each session to cure before continuing.

As for sanding it out, it could be done, but on such a large flat surface, I wouldn’t recommend it. Just like in automotive bodywork, large flat panels are difficult to get perfectly flat again. You will have to block sand the entire mold with a longboard. You will probably have to resurface it also.

#7

alright, I will do that then. How long are you waiting between your layers?

#8

http://www.fibreglast.com/learning_center_brochures/mold_construction.pdf

Try this article…and you might want to look at the other ones on the site also, GREAT deal of information there!!

#9

I have hundreds of molds under my belt I just couldn’t figure out why it was all of a sudden doing it now. I have done the same layup over and over again with no problems and now it happens. I am going to try and do less layers at a time and see what that does!

#10

At what mil thickness is the tooling gel coat applyed? More the better but the above talking about placing the first layer down while the gel coat is in late “B” stage and then allow it to fully cure over night is great advise too.

Also cut back on the Catalyst % (more work time too…). It is better to have it sticky for the first few layers and hotter later on to seal the back of the mold. Less shrinkage.

Shrinkage rate will do that to soft gel coat almost like it is nearing alligatoring…(I think I sent your a booklet on alligatoring…didn’t I?).

Also, watch out for large air pockets between the gel coat and first layer too

#11

well we have just about no air pockets throughout the whole piece. Also we usually let the gel coat sit overnight before we lay our layers on could that be a factor as well? We are going to reduce our catalyst and also just do little layers at a time

#12

That could be a large part of your problem. Polyester resins shrink excessively when there is no reinforcement present. You should put down at least 1 layer of reinforcement asap after laying your gel. The rest of the backup laminate can wait if necessary. I have done a few molds (that have been rebuilt) where I literally watched the gelcoat pull from the surface of the plug. There have been other occasions where I have sat and watched the gelcoat crack due to shrinkage.

#13

that sounds right but again the funky thing is, I have done hundreds of molds my same way but never had this problem. I will try all the suggestions lol

#14

how long do you let your stabilizing cure, full cure or B stage it?

#15

after the stabilizing layer is layed up, you can let it sit for as long as you want. (within reason of course).

#16

i am talking before I lay my other layers on it. I layed 3 molds this morning about 4 hours ago, and just wondering when I can lay the other layers

#17

Has it been extemely humid or raining while your spraying gel?

#18

Id say you could lay up after the heat cycle is over.

Those infrared guns that measure heat would probably help you out. Once the thing is on the down cycle for heat, you know its going to be a short time till you get to finish up.

#19

Late “B” staged…press a fingernail into the gel coat but no resin will be on your glove…

#20

no just hot, we are in a dry area so it only rains a couple tiems a year, but snows like a mother lol hahaha

Id say you could lay up after the heat cycle is over.

Those infrared guns that measure heat would probably help you out. Once the thing is on the down cycle for heat, you know its going to be a short time till you get to finish up.

Thanks, that is what I wanted to hear, that should speed the process up a little!