WTF happened???

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#1

Somebody help me here…I spent weeks making this plug, now it’s trashed.

Here is the plug flanged up and getting waxed:

Here is after brushing on the gelcoat…I used a digital scale and mixed it exactly at 1.5% MEKP. I noticed that it dried REALLY fast…basically overnight. It wasn’t tacky when I lightly touched it 7 hrs later.

Regardless, I forged ahead and laid down some chop strand mat:

And repeated the process several times sanding in between.

Then I pulled it apart and that is when my heart sank:( Notice the black top coat on the plug just basically dissolved.

The paint on the plug bubbled up…the only part that is reasonably smooth is where the aluminum flange was:

This is the smoothest part:

What happened??? Please help…thanks!!

#2

So after reading this thread, I’m wondering if the gelcoat reacted with the Rustoleum paint?
http://www.compositescentral.com/showthread.php?t=7421

And FWIW…my plug is also ruined. Total failure.:frowning:

#3

It looks like the polyester gel-coat reacted with paint. Next time: 1) Use PVA to create a barrier between the paint and resin, or 2) Use a better paint (catalyzed).

I always recommend testing an unknown combination for reactivity on scrap before you commit to using it to make a mold. Plug paint, release system, and surface coat resin are all factors.

#4

yes i had the same with ferrari mold. it is bad option of spray paint and polyster resin its reacted. so just sand parts now till smooth finish wax it good and do the same for mold not needed to use pva siple wax good . only not paint the part.

#5

In my experience, the only 2 paints that are useful for making polyester moulds are:

-polyester topcoat, or better, duratec. Disadvantage is that it needs rework after application. (sanding and polishing)

-2C PU paint. (after testing).

And make sure your gelcoat goes on nice and smooth. Work on your brush technique. (not related to this problem, but otherwise you might run into other problems, like alligatoring)

#6

gelcoat with 1.5-2%- MEKP should cure in a couple of hours.

I often (depending on the shape) coat my wood/mdf plugs and one off moulds with poly resin to seal then roll over over with a couple of coats of gell. Flat back, polish and wax. Its fast, cheap and works well.

All painted moulds I clear coat wet on wet and flat back for a class A finish