Plaster moulds?

[Talonmotorsport]

Has any body here ever used pink wall plaster to make a fibreglass mould? I'm using the blue foam used in model making and taxidermy, then sealing it with PVA and fibreglassing over the top. At this point I'm only looking at making one so I don't need a reusable mould. Whats the best thing to use as a release agent to put on the plaster mould when I come to laminating the new part?

It shrinks so no it's no good. There is a special plaster type stuff but canny remember what it's called, it's used by modellers as the mould can be made quick and used same day. No special tools etc but costs 3 times that of using fibreglass...

Best stuff to use when making moulds even if only for a one off part is gel coat and fibreglass, but even this can shrink if you do too many layers at once.

[Talonmotorsport]

Is it perchance called 'modrock' The stuff they use on broken arms?

nearly yeah you slap it on by hand but it's not very stable and beggar all will stick to it so if it cracks etc you cant really repair it...ooo and it;s like mdf, it acts like a sponge and soaks up damp so goes all shapes.

believe me it's easier to use grp it really is and it's cheaper too especially as you intend making a grp part from the mould. If mould is to make a one off part just make the mould using 4 layers then add wood to stiffen it.

What are you after making?

[Talonmotorsport]

My first project is making my own nose cone for my roadster FB (fat b***ard) as nothing else will fit. If I just cut and shut one it could end up looking alittle odd as it's a convex shape and I've changed all the angles. The next one is making a stretched escort cosworth type bumper for my transit (yes sounds silly but the kid in me says sod it).

Ummm dunno about the tranny idea ... but hey I got a daft bumper on my bus so don't suppose much different really .

I still say use fibreglass to make your mould as you may well bop both and need to make new parts, the plaster stuff is really only for one pull from the mould to capture the design.

What you need is someone who knows how to play with grp to point you in the right direction

[Talonmotorsport]

I'm not completly clueless with shaping the plug and painting it with 2k and polishing it, it just the materials I'm alittle unsure with. I did a fair bit of mould design and theory at collage Btec in industrial model making. We covered the basics like the best way to split a mould to avoid non releasing returns etc but it was all for plastic injection machines. Unfortunatly I had to get a job and I did'nt finish the course. I'm lucky with where I live as there are 3-4 large yacht builders within 6 miles of my workshop so I'll see what can walk out the back door when no ones watching. Any pointers greatfuly received in these sticky matters though.

[ayjay]

I,ve done a bit of moulding and the advice so far is generally good.

However if you need to design a body panel from scratch then plaster is a good idea. It willneed a fair bit of sanding ,scraping ,shaping smoothing (all the s's eh!) in order to make a model .You could then use that to make your pattern mould out of GRP.
You would save a lot of time by making a rough shape out of polystyrene blocks but slightly smaller than needed then smooth on your plaster . then the hard work comes to refine the shape as S's above.
Dont use pink plaster the stuff called "onecoat" is a lot more forgiving and easier to handle( white in colour --Wickes etc)
You can easily stop it cracking by reinforcing it with thin bandage and shave it down with an angle grinder(not indoors) .Get the final mould surface with something like car body filler fine sanded to the final shape.
We used to use silicone spray as a release agent but theres probably something better specially for releasing GRP.Hope this helps---ENJOY

Imagine you have made your plug and it's shiney ready to mould...use honey wax to wax it about 5 or 6 times then decide where your shuttering needs to be to allow removal from the plug....when shuttering sorted pva release using a sponge, let it dry then gel coat, leave this to go tacky..ie you can leave a finger print in it but nowt on yer finger then startlaying up...when you have got the layers needed take the shuttering off and lay up the other side to create your joint......simples really.

Grab someone from the boat yard and barter with a few pints you might even end watching him do it for you...