Mold problem

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#1

Hey guys,

I made a mold of the roof of my BMW, but it didn’t worked that well. I did everything like before but today when I pulled the hood out of the mold I found out that there are some kind of holes/waves on the surface of the mold and particularly on the gel coat.

It’s the first time I experience such problem (and I’m relatively new to mold-making). I made some photos, so you can see for yourself.

What can cause this phenomenon? What I did was brush PVA, brush polyester gel coat to the roof, let it tack, then a layer of 2x2 80 gr. glass fiber, brush polyester casting resin, layer of 450 gr. CSM, brush casting resin, layer of 450 gr. CSM and a final layer of casting resin.

Thanks in advance!

#2

Looks like you over heated the gel coat?

#3

You can make your own epoxy tooling gelcoat which is very easy to make and work with. I have never had any kind of wrinkling, or any issue of any kind while using an epoxy top coat.

Simply mix your filler of choice, with your laminating epoxy of choice, and add a little of epoxy pigment to bring some color to the molds surface.

Then brush a couple of layers onto your plug. Your first layer should be fairly thin to allow bubbles to rise to the surface of the gelcoat. Wait 5 or so minutes after application, then sweep the gelcoat with the flame from a torch. This action will pop most of the bubbles that are at the surface of the epoxy. Let each coat cure to a state where it is still sticky, buy won’t stick to your finger when touched. When the second coat has cured, begin your lay up with fiber glass cloth and clear epoxy.

I’m not the best at mold making yet, but this is the kind of result I get from making molds this way.

Let me know if you have any questions.

#4

The picture shows an undercured gelcoat, attacked by the subsequent layers.

remedy:

-more catalyst
-stir better (if the “elephant skin” is patchy)
-more heat
-thicker layer of gelcoat

#5

Well, I don’t think it’s possible…it’s freezingly cold out here.

Thanks, man! Otherwise I got you. I should contact my supplier and ask again for the resin/catalist ratio. It’s not patchy…it’s completely cured! Today I’ll try again with thicker coat…but heat would be a problem. It’s extremely cold in my workshop and I think that’s the problem!

Also I noticed yesterday that I released the roof from the mold very hardily. I had to pry with a screwdriver :eek: Is the problem in the PVA or again the mess with the gelcoat?

Thanks :slight_smile: That’s helpful. I consider trying to brush a few layers of gelcoat instead of a single thicker layer!

#6

What is the temperature in your workshop?

#7

I try to keep it around 18 C/ 65 F. But usually I stop the heaters for the night and it can easily fall down to 1 C/33 F.