From: bill@leeweyr.sccsi.com (Bill Lee)
Subject: Re: Help with release agents needed
Organization: Lee Aerie
Date: Wed, 27 Jan 1993 03:22:23 GMT

In article <21177@acorn.co.uk> cwatters@acorn.co.uk (Colin Watters) writes:
>
>Can anyone talk to me about release agents?
>
>I have made a polyester mould that came off its wooden plug very
>easily however I can't seem to stop epoxy mouldings sticking to
>the polyester mould very badly (I trashed one part of the mould 
>at the first attempt!).
>
>I have tried:
>
>1/. Bees Wax rubbed on and polished off - six "coats"!
>
>2/. A silicon spray used to lubricate windsurfer dagger boards.
>    (Yes I know about painting problems later with silicon).
>
>Both looked OK before lay up (nice shine) but in both cases the 
>epoxy stuck to the polyester mould better than it did to the kevlar
>cloth!
>
>When applying wax should it be left to form a kind of solid cost
>or polished off like on car bodywork? I find most of it seems to
>comes off as a white powder when I polish it even gently. Should 
>the mould have the shine taken off first before starting with the
>wax? Mine has a high gloss finish.
>
>Ta
>
>Colin
>
>
>
>
>
> ---------------------------------------------------------------------------
>|            _          | Email: cwatters@acorn.co.uk (Colin Watters)       |
>|    _      \ \         |                                                   |
>|   | \______\_\_____   |---------------------------------------------------|
>|   |-________--_____\  |                                                   |
>|            / /        | Do it by remote control !                         |
>|           /_/         |                                                   |
> ---------------------------------------------------------------------------


I've done a lot of epoxy moulding (molding?) making propellers for
my Control Line racing activities. The best release agent for epoxy
is PVA (Poly vinyl A-something. I've heard Alcohol and Acetate.
Don't know which. Don't care. It's PVA and you should be able to
get it where ever you buy the epoxies you are using.)

PVA is a thin, green liquid. It is water soluble but insoluble in
epoxy. The trick is to put it on over a wax base.

I use Johnson's Paste Wax. You can buy it in almost any grocery
store. It comes in a yellow can about two inches high and about 4
inches in diameter.

Make sure your mold is clean. Wash it thoroughly with hot, soapy
water. Once it's dry, smooth on a thin coat of the Johnson's paste
wax and let it air dry. DON'T POLISH IT! When it's dry, it will
leave a slightly dull coating on the mold.

Brush on a coat of PVA. I use a 3/4" modeler's brush. The dull coat
of wax will grab the PVA and prevent it from fish-eyeing on you.
(This is probably what happened to you previously: the polished
surface allowed the surface tension of the release agent pull
the film apart before it could dry.) If the PVA still trys to
fish-eye, brush on another thin coat and quickly blow some warm air
out of a heat gun or hair dryer on the PVA to force-dry it before
it can contract and break the release film.

This procedure has worked well for me over the years. I've molded
many props and have never had one stick to the mold. (I've had
other problems, but not this one!).

Regards,

Bill Lee





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