Hi all,

polyester body filler is notoriously bad for causing moulds to stick to patterns. You are better off coating it with a resin system compatible with the mould system you plan on using.  That way once sanded smooth and polished, you have a good surface that shouldn't cause any sticking issues.

Be cautious of paints, even 2k paints as they can stick if any solvents are left within the paints as the solvents tend to outgas a little, eat through the release agent thus causing a sticker.

If you are worried then use PVA as a good even layer of PVA mould release will form a physical barrier ensuring a mould won't stick.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

I've moulded from filler before. Warrens right, it takes some serious sealing!  I've always flatted back with some 600 and sprayed it with gloss blue pva release.  Dust the first few coats until you get a good blue layer.  This stops it fish eye-ing.  Once you've got a good blue layer lay down a full film. The gloss pva will give you a shiny finish on the mould so you should only need minor polishing.  To have the mould fall off the plug add a layer of wax onto the pva and give it a good buff.

I've never used PVA release agent, will it affect the surface finish of the mould? I don't mind if it's a negligible effect that can be easily flatted and polished out.

It will affect the surface, yes. How much refinishing the mould needs will be determined by how well you can spray the PVA, but even the best coating will need a little bit of refinishing. PVA tends to run and fisheye worse than paint, so as FLD said you want to spray several light mist coats initially and let it dry completely between each. You can then spray heavier coats, but be careful not to try to load it on as heavy as you would a paint - it will run! 

If it helps I'm using a devilbiss Sri with a 1.4mm tip. With plenty of dust coats I don't get any runs or fish eyes and leaves a nice glossy finish similar to a lacquer.  It's cheap and just washes off with water so give it a go and see how you get on.

Just a thought....

Thanks for the offer but I'm in central Scotland so a bit far. I have a devilbiss with 1.3 tip so can give it a go with that.