Tips for applying PVA release agent on moulds

Its only half metalwork but I'm pretty sure some of you guys will know a bit about this!
In point form:
1) Casting epoxy into a CNC machined mould.
2) Having problems with getting a consistent surface finish.
3) We are spraying the PVA release agent using a small touch up spray gun.
4) Sometimes we get small runs.
5) Sometimes part finish is matte due to the PVA drying too quickly.
Being a novice I think these problems are pretty much down to application technique.
Any tips on what we can try to make the process of applying the PVA more forgiving?
Alternatively would making the next mould from Teflon be worth trying?
I don't know if the machining finish would be smooth enough but my guess is it could be used without a release agent.
Any ideas or experience?
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A long, long time ago, I worked at a place that made parts for medical equipment from glass filled epoxy. They used silicone rubber for the molds with mold release compound from a spray can. The finish out of the mold was pretty good, but the parts needed to be polished up with a buffing wheel to look consistent. The molds were a pain to make because you had to de-gas the silicone after mixing in a vacuum chamber, but they lasted pretty well.
BobH
On 06/17/2016 11:18 PM, axolotyl wrote:

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On 06/17/2016 11:18 PM, axolotyl wrote:

I've not used PVA mold release but I have used aerosol spray-on silicone mold release from www.smoothon.com in aluminum molds to cast their polyurethane, usually shore 70A rubber (part PMC780). They recommend spraying the mold, then brushing with a small paint brush to get a uniform film, then letting it sit for 30 minutes or more to flow out and dry. I was casting small stuff, 1-3" max dimension, so used those disposable "battery" brushes, 1/4" or 3/8" wide. If I did all of that the surface finish was usually very good, as good as the mold. On prototype parts that I didn't care so much about I would spray, wait a minute, then start mixing the polyurethane. Those usually had a light fish scale look, with the occasional run still visible :-). Anyway, maybe the same technique would work with your PVA mold release?
----- Regards, Carl Ijames
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On 19-Jun-16 12:00 AM, Carl Ijames wrote:

Thanks Bob & Carl.
I'd not thought of pressure pack mould release. I'll check that out as its a easy thing to try.
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