Ah I forgot EC are uploading their latest videos to Vimeo. This is the updated one here:

http://easycomposites.co.uk/#!/composites-tutorials/High-Temp-Tooling-Gelcoat-Putty-Mould


Realistically you should be able to use the PETG  covers, it may just be a good idea to use a release agent rather than relying on the self-releasing properties of the PETG. Epoxy really shouldn't react with the plastic in any way, I'd be very surprised if it did. So you should be able to use a release wax, or Easylease would be ideal - but the solvents in the Easylease could potentially attack and dull the plastic, I'd do a small test first. Or worst case: PVA guarantees success.

Thanks Hanaldo,

I was going to use Easylease anyway as I keep in stock,  and maybe apply a few coats of release wax first.  I don't know if it's the recommended thing or even if others do that on a regular basis ...........  apply release wax,  wait for it to dry,  then apply a thin coat of Easylease.  I've done it before,  seemed to work OK.

It doesn't matter that the PETG form ( prototype headlight cover )  is damaged or dulled,  it's a 'use once' sort of thing.  It's specially vacuum formed for the purpose of creating a single solid mould.

Many thanks for the video link,  that's the one!  



TURK

Oh, never apply a solvent based release agent over a wax release agent! You can apply wax over the Easylease, but not the other way around. The solvents actually dissolve the wax, and the wax contaminates the polymers in the chemical release agent, rendering both useless. You may have got lucky the last time you tried it, or maybe you tried it on some plastic that had good self-releasing properties anyway?? Either way, just swap the order and apply the Easylease first and then the wax.

I would still test that the Easylease doesn't dull the PETG. It may not matter for the PETG part itself, but the finish will be replicated in the mould so it saves a lot of trouble later on.

Easylease should be applied in layers, typically a minimum of 6 layers for a pattern or new mould. Check the TDS for details, but it will be something like 15 minutes between coats. 

Ah, yes,  I'd forgotten about that .................  been a while since I used it.  Thanks Hanaldo  

I'm going to order from EC today.
EG60 Epoxy Tooling Gelcoat
EMP Epoxy Moulding Putty

I think that 10 Kilo's of the putty will be enough for two headlight covers.  D'you know if I can build it up,  a nice few layers like 4cm thick,  is it OK to do that?  Also,  how thick of a gelcoat can I realistically get away with.  The thicker the better!

I'll keep you informed of how it worked mate,  about time I updated my 'Quad Headlight Project' anyway.  No doubt some members will find some of the methods quite interesting >  Quad Headlight Project
The very first picture you see in the link was my very first attempt I did of the dual aperture headlight cover.  I vacuum formed it using a home built vacuum forming machine,  unfortunately I could only vacuum form up to 1mm thick ABS.  I was so impressed by that thermoforming method, and it's potential that  I eventually went out and bought a FormMech vacuum forming machine!  



TURK

I'd be hesitant to do 40mm in one hit, I think much over 25mm in one go may provoke a pretty high exotherm. You could do it in 2 layers, you would just want a 'coupling coat' of the gelcoat in between the layers, which is a bit of a waste really. I'll let EC clarify on that as I'm not too familiar with their putty specifically.