I am using a MDF mould buck which I need to 'smooth' with primer and top coat of paint - I propose to use a nitro-acrylic paint - will that work with a gel coat and polyester resin which will be used to make the mould?

Thanks

Polyester and Epoxy are compatible.

Polyester and Urethanes are for a very short time period. If the poly is under the urethane it will off gas and eventually create bubbles in the urethane and ruin your plug. I ruined many, many plugs this way before some one mentioned the compatibility issues.

When building plugs Polyester primer is all you need. It can be polished to a mirror. Really is no reason to use anything else.

For bonding always use epoxy and under 100 grit sand paper for prep. You’re relying on a mechanical bond if youre bonding post cure. Bigger scratches for the epoxy to bite into, the better.

Jason

+x

 

JasonFL - 4/13/2019 2:43:49 PM

Polyester and Epoxy are compatible. Polyester and Urethanes are for a very short time period. If the poly is under the urethane it will off gas and eventually create bubbles in the urethane and ruin your plug. I ruined many, many plugs this way before some one mentioned the compatibility issues.When building plugs Polyester primer is all you need. It can be polished to a mirror. Really is no reason to use anything else.For bonding always use epoxy and under 100 grit sand paper for prep. You’re relying on a mechanical bond if youre bonding post cure. Bigger scratches for the epoxy to bite into, the better.

So I'm not using Urethanes but Acrylic - didn't manage to find any polyester primer in time - but acrylic paint seems to be compatible when over-slapped with gel coat/ polyester resin/glass fibre?

The mould will therefore be polyester and I will fill it with Epoxy Carbon Fibre - all as per the bonnet EasyComposite tutorial... which is extremely clear!
I think I will bond the steel in with the lay-up of the carbon fibre so there is a chemical bond over and around the steel for maximum rigidity - good idea or not?
Final piece of the puzzle - when I connect the top and bottom parts I will have a hollow piece which I want to fill with some kind of expanding foam - anybody done this?

Thanks for all your help so far - great forum!

I’m not sure what youre using the steel for. Is it to add rigidity to a mould or a finished part?

If for a mould, youll need to insulate the steel with E glass to protect it from the Carbon, OR, completely seal the steel off from any oxygen exposure to prevent galvanic corrosion.

Also, sand the steel with 40 or 50 grit paper thoroughly. Clean it in uni directional wipes with acetone multiple times. Using a swirling motion just spreads residual dirt and grease around the metal. Add the metal to the layup shortly after the acetone evaporates.

The foam idea sounds good. Is it needed though? Also are you using it to add structure or floatation? Use 2 pound foam for floatation, and 4 pound or higher if youre looking to add some rigidity.

Jason

if there is an epoxy surface coat you have nothing to worry about. If it’s epoxy and carbon without a finish then it will corrode over time.

I’d use two part expanding foam with a 4 pound density. I’d avoid the stuff in a spray can.

Jason