Gelcoat gets wavy on vertical surfaces of mold

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#1

I’ve tried twice with the same result. I’m trying to build a small center console which has 3 vertical surfaces and 1 horizontal, kind of like an open box missing 1 side. My plug is nice and straight but after I pull it from the mold, the vertical surfaces are wavy in some spots, usually near the bottom by the flange. They are low spots in the mold, sometimes up to 1/8" deep.

I’m brushing the gelcoat on since it’s only about 12"x12"x2". I put down 2 or 3 layers about 4 hrs apart. It’s hard to get uniform thickness with a foam brush, but it’s about 20-25 mil in most places, some might be a little more like 30. Any ideas?

The horizontal surface comes out nice, save for a tiny bit of 'gatoring, which actually looks more like a small spider web and it’s so small (<1") that I can fix it. The smaller vertical surface is not as afflicted, but still gets some wavyness. Could it be to too much MEKP for the conditions? It was a bit hot at 85F and I still used 2%. Gel too thick in that spot, or too thin, causing a weird reaction? Maybe shrinkage? I might have waited a little too long (8hrs) to put 'glass on it.

Any help would be much appreciated.

#2

i think since you are putting it in layers, that is your problem. i have done that before and the second layers dried and shrunk a little and made the first layer wave

#3

Yes, cut back on the MEKP.

You don’t need to wait 4 hours inbetween the gel coats, only when it B stages (leaves a finger print but no resin on the tip).

Likewise with the lamination to, B stage and lay it up.

#4

Thanks for the replies.

I was worried about gatoring if I put the second layer on too soon, which is why I was waiting 4hrs. I’m not positive I can get a good, uniform 20-25mil thickness, especially on corners and vertical surfaces with the brush, which is why I was doing 2 layers. I’m also using PVA so I’m going to have to clean up the surface some and I was worried about it possibly being too thin (like 15mil) in some areas. I was curious why it’s only the vertical surfaces that do this, but I guess it’s because they’re closest to the outside where it can pull from. If I apply a second layer, as well as my first glass layer right after B-stage, should I be ok? Or should I skip the 2nd layer and go real thick and possibly have some 30-35mil spots, but probably nothing less than 20mil?

When laminating I put 3 layers of 1.5oz csm and let that cure maybe 3hrs and then put on a couple more layers. Sound ok?

How much MEKP would be good for ~85F, 1.75% for gel? What about PER?

#5

You might have a better chance of getting more uniform gel coat coverage if you used a normal bristle brush, rather than foam. Personally I would also forget about the PVA and use wax, as this seems to me a much better release agent for small parts, especially if you are applying gel coat with a brush.

#6

have you considered spraying your gel? even if you use a really really basic gun such as a splatter gun… you have much more control over your gelcoat and it has less chance of running which can also cause styrene buildup and cause problems… plus the gelocoat is much thinner and with a brush, you really cant control the thickness of the gell as when you first touch the brush to the mould, its full of gelcoat to the end of the stroke where its streaky and really thin…
i have reverted back to brushing gel unless im mouldmaking, it is quicker, easier and less mess, but for a better finish id reccomend spraying.

#7

I use wax on flat panels, but when I used it on this plug on the first mold attempt, it stuck and destroyed the plug :mad: I’m using PVA just to be safe when making the mold.

I use a foam brush because when I tried a bristle brush it just caused streaks and brush marks where there’d be low spots.

I’m very tempted to get a spray gun, but these are such small parts that I thought brushing them would be ok. I’ll probably give it one more go with the brush and then give up and get a cheap spray gun. Cup guns are expensive.

#8

Guess a lot to do with laminating has to do with experience, and this is possibly the reason why those new to this sort of work seem to have the sort of problems those with more experience have only very rarely.

Personally I read a few good books before even attempting to lay anything up, and find this helped me to avoid the really silly mistakes, which I would have almost certainly made otherwise.

#9

I agree, use a bristle brush.

I was taught to apply 1 layer of gel coat using horizontal brush strokes across the mold and then apply a second coat with the brush strokes going vertically across the mold.
This way you get an even coverage with no fish eyes appearing in the gel coat.

#10

Welcome jmc123 from J. Mc…:wink:

#11

Cheers :slight_smile: i thought it was about time i posted something :wink: