I have made up a male mold for my rear boot lid.

Its had 4 coats of the recommended wax type and buffed up so that no trace of wax remains.

I have now painted it in pva release gunk that is a dark blue. After an hr or so it does not seem to have dried evenly - it has clustered into 'pools' of blue, and the areas where it was dont show any sign of colour.

Im wondering - does the pva leave something behind that I cant see and that isnt coloured blue, or do I have such a shiny non stick surface that its repelling the pva?

any experience here is welcomed before I wreck my mold by gluing gel coat to it!

atb

steve

Ah the dreaded PVA rash....yes it does have a tendency to pool up like that.
And, the colour should be fairly even and show everywhere.

How did you apply it? Spraying very thin coats is the best, next best is by using a sponge and dabbing lightly.

In the past I've made the mistake of under-doing the PVA....it does not leave anything behind you can't see.........if you can't see it there's not much on......

HTH

Alan

thanks Alan.....that shows I have a bit of a problem.....

I used a smooth surface kitchen counter top as the main surface - cos it had nice radiused edges. Where I needed corners where there werent any, I made em up from body filler. The PVA does not seem to stick well anywhere - inc the filler parts.

I have tried using a hand held sprayer - first one got dissolved by the stuff! wnd one wasnt that even, so I have used a brush.

I dont think there are traces of wax on it - its all been well polished. However, this does seem a bit silly - surely a waxy shiny surface WILL make anything painted on it tend to pool off......

I will try another couple coats.....hopefully if the pva doesnt stick, neither will the gel coat - just hope that doesnt pool off too or im gonna be looking at other means.....sanding off the wax will be my last attempt.....hope thats not the case.

cheers for the advice

Steve

Yeah, I completely agree the logic you suggest. If the waxing is really good (and sounds like it is) and the PVA is plentiful...then I think you'll be OK.

My only problems have been when I have gone too thin with the PVA trying to avoid the pooling......I think you'll be OK....

If you aren't going for unpainted gel finish (which I'm not) it is MUCH better to sand off a little PVA rash than unstick a part in a mould...:-)

this is looking like pretty comprehensive pooling and it dont wanna stick anywhere......im gonna wipe it off I think cos it just seems to be wrecking the surface.

I can :

1. try it with just wax and hope the gel does not do the same thing...

2. try a bit of gel on just a small area and see if I can release it afterwards using wax only....

3. fine sand the friggin wax off and use just pva


This is a proper mold release wax.....and I did polish it off so im a bit mystified...

atb

steve
Rescued attachment Dcp_3088.jpg

Oh...er...I see what you mean...that is MASSIVE pooling......almost certainly caused by the brushing....if the wet volume isn't there then it can't form big pools.......the pooling I meant is more like a hammerite paint finish.

PVA is water soluble, so I'd wash it off and then re-try with a sponge just dabbing on thinly.

Wax without PVA is often done in mature mould...but never the other way round.

So my advice, rinse off, re-buff, then re-PVA with a piece of sponge.

Just to throw a spanner in the works, my mate makes boats of the glassfibre variety and he doesn't use pva release agent in his molds but does use a wax polish release agent....surmise from that what you will but his boats come out kin fablious. and they cost shed loads so the people that buy them (and there is a waiting list) must think so too..

thanks for the advice alan and viper.

thats actually after I added some with the spray - it still runs off!

I then spread it around with a sponge, and it STILL runs off. Its as if the surface is oily or something.

Its all off now. Will give it another buff up tomorrow. If it still runs after sponging, im gonna sand it with light grade paper and see what happens.....

If it was just the melamine like surface, then id think it was that....but its the filler sections too....

atb

steve

Main thing Steve is to put it on thinly...maybe even using a bit of kitchen roll or similar.....

this is my pooling...hard to see at this resolution...more like orange peel than big puddles...

I think I have sussed the problem.

I did a couple of tests.

The first was to get a bit of scrap material that hadnt been treated with wax. Painted it with a brush, spread thinly and left it overnight. Its dried without any problems at all!.

2nd test - drag a finger at pressure over the mold surface and.............it gets coated with a thin film of wax.

So, I need to give the thing a really hard polish off as any remaining seems to really cause a problem. Makes me wonder why I bought this really expensive wax if its all gotta come off with virtually no trace or it repels the water carrier......


atb

steve

Steve

I had the same problem with a set of mud guards, although not so dramatic. To get round it I used a sponge and several thin coats of release agent, which I put on in thin long strips which overlapped. As I finished a coat I gently passes some warm air over the surface to dry it before it could pool, I then put on another coat.
It took some practice to cover completely and avoid streaks but once the end product came out of the final mold it had a thin layer of release agent holding onto the surface which can be washed off or peeled off.

Nick

[Edited on 1/4/03 by Nick Davison]

One of those Eureka moments.....

my first mould came off the buck with 10 mins or so of prising and teasing with wallpaper scrapers down the side!

A few marks from the over generous PVA, but nowt a bit of sanding and primer surface on the final part cant cope with.

Its amazing how thin five layers of 300gm fibreglass comes out....gonna re-enforce it with an alu backing.

Have been a bit suprised how expensive making fibreglas parts for a whole car is. If I were making a book car, i recon it would be cheaper to buy than to make. But im not, and have no choice and lots of bits to make for the Morgan look.

Anyway, at least I have made a partial start!

atb

steve

[Edited on 7/4/03 by stephen_gusterson]