andrew-theasby
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| posted on 13/12/10 at 12:21 PM |
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worried about a mould sticking
Hi, ive done quite a bit of fibre galssing before but this is the first time ive made a reuseable mould. After reading various tips on here and
online, i made a male mould, then with plasticine and allysheet blanked off one half ( to lay it up in two seperate halves) then waxed the surface
with "macwax" a runny wax release agent that we use at work for other jobs, then sprayed PVA on. The PVA went blotchy so i wiped it off
and tried thinning it with warm water, and made a mess of it again  . Ive since read on line that no pva at all is better than thinned PVA? but in
the same sentence they say 15% of all new moulds get stuck. Obviously i want to reduce this risk as much as poss so does anyone have any advice for
me to proceed with? Ive cleaned the mould up now and have a painted/lacquered surface on it. I want to apply the release next then a polyester
gelcoat, then the cloth. Any tips much appreciated please..
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CNHSS1
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| posted on 13/12/10 at 12:28 PM |
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i use lots of quality mould release wax coats, then panic and add a few more, and usually anothre 2 or 3 for good measure!
basically id get the mould as 'release friendly' as poss in terms of release angles, then paint with 2pk or similar, then add at least 10
coats of wax buffed off well between each. If the finished article is likely to be prepped and painted, id use PVA release agent too (not any old PVA
though, the release agent has another component to make it suitable for the job), but the pva can be seen in the finished moulding if you are looking
for an A1 not-to-painted item
"Racing is life, everything else, before or after, is just waiting"---Steve McQueen
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markt0121
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| posted on 13/12/10 at 12:31 PM |
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What type of paint did you use on the mould? I've heard you need to take care that the acetone in the resin does not eat into the paint and its
best not to paint the surface. If you post the type of paint maybe some experts on fibreglass can advise how to deal with it.
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andrew-theasby
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| posted on 13/12/10 at 12:35 PM |
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Shape is very release freindly on 1st side, so you just reccomend lots of coats of ordinary wax, nothing else then?
The other side is still a good shape to release, but a few intricate bits which would be difficult to polish round, would leaving the wax on
matter?
And it was 2k lacquer, but it might be a bit thin now where ive rubbed it back again
[Edited on 13/12/10 by andrew-theasby]
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Fred W B
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| posted on 13/12/10 at 04:13 PM |
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10 coats of wax works for me, if it is not all rubbed off you will see the unevenness/texture in the mold surface.
Cheers
Fred W B
You can do it quickly. You can do it cheap. You can do it right. – Pick any two.
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Triton
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| posted on 13/12/10 at 04:15 PM |
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Wax wax and more wax....polish it all off as wax left on will etch the mould... n the past I have waxed 6 or 7 times and used pva straight from the
bottle using a sponge to lightly apply it. let it dry then gel coat it, when ready get laying up.....simples really.
My Daughter has taken over production of the damn fine Triton race seats and her contact email is emmatrs@live.co.uk.
www.tritonraceseats.com
www.hairyhedgehog.com
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andrew-theasby
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| posted on 13/12/10 at 11:33 PM |
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Can you polish the wax off too much? Do you polish off between each coat or once after the 6 or 7 coats have been applied? Thanks. Can i just use
pva on its own on the tricky bits?
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Steve Hignett
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| posted on 14/12/10 at 12:51 AM |
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Andrew,
U2U me your number again, I'll call you tmrw afternoon (?) And can give you some mould release wax and/or pva...
Steve
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Fred W B
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| posted on 14/12/10 at 05:39 AM |
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quote:
polish off between each coat
I put coat one on, let it sit until the wax is just about dry (but not too long or it is too difficult to polish off)
Polish off
Let it sit for a while - up to an hour (get on with something else in the meantime)
Put coat two on, repeat etc, etc
Yes , it takes ages, spread over several sessions. I make a note of the time I finish each stage on a piece of tape next to the area so I can remember
what layer I am on.
Cheers
Fred W B
 
scuttle mold prep 001
[Edited on 14/12/10 by Fred W B]
[Edited on 14/12/10 by Fred W B]
You can do it quickly. You can do it cheap. You can do it right. – Pick any two.
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coyoteboy
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| posted on 14/12/10 at 01:36 PM |
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This is a black art I'm sure. I've done loads of composite bits and pieces before but the one time I didn't want a sticky situation
I got one and ended up having to buy a replacement part and later burn the GRP off the item I was copying and respray it. Grrr. Ilove threads like
this.
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suparuss
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| posted on 17/12/10 at 11:12 AM |
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Pva is ok if you know how to use. ive been using 2-3 coats of number 7 release wax and then pva which works fine for me.
the trick with the pva is to spray in on in extremely fine coats.
literally one or 2 quick wafts of spray on a really fine mist setting is what you want to buld it up. i usually put about 10-15 coats like this. wait
30mins between coats.
if you can see it going on to the mould then it is too thick and will run and become blotchy. when you have about 10 coats you should just be able to
see faint blue hue to the colour of your mould (if it is white or a light colour)
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andrew-theasby
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| posted on 17/12/10 at 11:19 AM |
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Thanks, ive managed to get the first half off succesfully today but ill try that next time, do you have to clean the gun out between each coat, will
it set in the gun? I think painting the mould white is the most important thing i hadnt thought about so far if anybody else is following this
too.
PS thanks very much steve for your advice the other night, gave me the confidence to go ahead with it. Will post some pics soon.
[Edited on 17/12/10 by andrew-theasby]
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suparuss
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| posted on 17/12/10 at 11:32 AM |
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ive had the pva in my gun for about a 2 years now! should be ok. 
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andrew-theasby
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| posted on 17/12/10 at 11:39 AM |
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Really!! Just out of interest, how do you spray gelcoat, do you thin it or is it a special gun?
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suparuss
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| posted on 17/12/10 at 12:12 PM |
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i think you can get a special gun for that, i think its about a 3mm nozzle or something. probably needs a big compressor too. ive never bothered as i
only do bits and bobs for the car so brushing it on is adequate for me.
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