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Cracks in SMC

Old 04-22-2018, 08:26 PM
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MajD
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Default Cracks in SMC

I'm starting the paint prep on my 79. I wanted to see what I was dealing with since the paint is heavily cracked over most of the car. I selected a door skin and started removing the paint. The cracks were in the grey primer underneath the paint. There was a black layer underneath the primer that I assume is a gel coat, but I thought SMC didn't have a gel coat. Anyway, the cracks were in this layer and even the fiberglass underneath. Here are some photos:







Texture in the gel coat



Gel coat and exposed SMC

Small cracks in SMC

The SMC cracks are very shallow and do not hold lacquer thinner.

Can I just remove the paint and primer down to the gel coat and then sand it smooth? Once it's smooth, can I cover it with a build primer to help fill in any cracks, or will the cracks reappear because they are in the SMC? Thanks.

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Old 04-23-2018, 08:55 AM
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There is NO gelcoat on this SMC..so you were initially correct.

Get all layers of the SMC and that includes the thin black primer. THEN look at it again.

Normally SMC will not micro crack due to how it is made and its strength UNLESS it has been hit hard and the panel stressed. Careful inspection is required in some areas and IF the panel can be physically forced by hand to see a crack open up...that is what may be required in some areas that allow you to do just that. Like I wrote. Normally SMC does not micro crack like the old press molded polyester fiberglass.

Once it has been inspected and all appears to be good...apply whatever primer you choose to work for your situation.

Photo1: I can not see much of anything resembling crack.
Photo2: I can see what looks like bad cracked paint in the light reflection.
Photo3: I see cracks at the top of the door handle area that look like they are in the paint.

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Old 04-23-2018, 03:00 PM
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Default Thanks.

DUB, thanks for the info. If you enlarge the first picture you will see thin black veins that look like cracks in the fiberglass. I thought it seemed strange too but didn't know what else it could be. I have pressed on the doors and they seem solid. Thanks.
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Old 04-23-2018, 05:12 PM
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I guess I would have to take out my jewelers loupe and really magnify the cracks in the first photo and see what is going on with them.

If you have any doubt...block a small area and see if the cracks go away.

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Old 04-24-2018, 08:38 AM
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You are right about loupe, they are very shallow and I cannot feel anything when I rub my fingers over them. I will try the blocking and see what happens. Thanks.
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Old 04-24-2018, 08:43 AM
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I hope a good blocking takes them out.

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