| What seems easy to
others always seems tough to me. Nobody I know has a problem
with applying PVA release agent to a mould, so its really
a waste of time writing this article. But just in case YOU
do, here are my experiences.
I have always brushed it on, straight from the bottle. The
results have been very consistent: that is, always lousy.
For a long time I brushed it on over QZ11 silicon wax. Then
one day it decided to fish-eye, and refused ever to lay down
on QZ ever again.
No real loss,the QZ was building up in the
mould and slowly ruining it.
After a switch to PLP1, things got better and I carried on
brushing:
still with lousy results. This became critical when I went
to larger moulds, so I asked around. One said buy the most
expensive Yak's fur brush from an artists shop and use that;
I did, and produced magic Mongolian relief maps on the surface
of my props. One said spray, so I did. Wonderful orange peel
effects, but I preferred the Gengis Khan results. The PVA
seemed to have too much surface tension, so I tried thinning
with water. This helped a bit, but evaporation was slow, and
there was a strong tendency to get runs. More advice, this
time from a real expert; thin with metho. Well, I added some
metho and everything turned white, globs sank to the bottom
and disillusionment really took hold. I tried fresh metho,
fresh PVA, nothing helped.
Then I asked these experts if they had actually
done what they said. Well, no, but it should have worked.
They actually wiped it on with a rag, so thin you couldn't
see it. That's OK for some, but my moulds are pretty rough
and I need some thickness in the PVA. So it was back to brushing.
This time the PVA seemed to crinkle up, like
a dust bag had been emptied onto it. After washing this off,
I tried again. This time it went on fine, in some places,
anyway. Crazy, sheer bloody-minded chemicals. So I asked a
chemist, the scientist type. No idea.
Well, an idea came to me, after mixing with
water the soluble oil for my milling machine. You must add
the oil to the water, not the other way around; a bit like
adding water to concentrated nitric acid, you only do it once.
So I figured the same might apply to PVA , and came up with
this recipe.
I added 15 parts metho to 15 parts water, then
stirred it. Then this solution was poured into 70 parts of
PVA whilst stirring. Vunderbar, no white precipitate and the
solution was nice and runny ! Spraying was now much better,
no fish-eyes and quite controllable. Some care was still needed
in getting a wet enough spray onto the mould, but the runs
were gone and the results great. No dust bags either. Warming
the mould helped a bit as well, especially as it was mid-Winter
in Perth.
So there it is, hope it works for you. |
