GRP mould material ?

[duncscz]

Any recommended material to create a simple GRP mould to produce a replacement piece for the bonnet catch mount. I can produce the basic mould in wood, but I'm worried that the GRP will stick to the wood itself. What can I line the mould with - polythene ?

[fly boy]

Mould release aerosol...

Shame you'er not local I could have got you some from work...

[GreenV8S]

Not done fibreglass molding myself, but I think it's normal to prepare the mold to a smooth finish and then paint a release agent over it. I think (could be wrong here) that the molds are often made from fiberglass or similar.

[ren32]

When I made a small box moulding recently, I lined the metal mould with a layer of kitchen foil, It's a bodge but hey, if you are not too worried about the quality of exterior finish it works! Just press it out the mould and peel off the foil afterwards.

[wedg1e]

Believe it or not, but brown parcel tape is a great non-stick finish - as long as the tape joins aren't a problem on the finished part.
And yes, GRP is itself often used for making moulds.

[Graham]

I've made quite a few moulds for bits of tasmin bits and the main ingrediant for the moulds are GRP!!!


my basic process is.


1) clean and prepare the original part to a smooth finish

2) 3-4 coats of a good wax

3) a coat of mould release agent ( i get mine from a local fabricators)

4) paint on a layer of gelcoat and wait till it goes tacky ( a few hours or leave till the next day)

5) layup grp matting and work in the resin. you want a mould to be 3-4 times heavier than the finished part if you are looking to make more than one item from it.


making a new part from the mould is simply the reverse of the above.

if you are taking a mould from a pattern made from say wood i use a high build primer to seal and get things smooth before waxing and release agent as above.


When making the mould consider how you are going to get the finished part out. It might be ness to make the mould in more than one part.

to do that i use some plastic sheet (3-4mm thick) hold tis in place on one side with plasticine, wax and R/A the other side and make the mould upto the the waxed side. when that part of the mould is cured, remove the plasticine and plastic, clean up the rest of the patten, prepare that and the flange of the made bit of the mould with wax and r/a and lay up the rest of the mould. before removing th two parts of the mould from the pattern drill and bolt the two halves together so when you want to layup a new part you can accuratley asseble the mould.


does any of that help ?

G

[duncscz]

Tks for all the advice. My first efforts for a simple piece used the packing tape/foil method, which was quite successful, though I was quick to remove the mould parts as soon as the GRP had set sufficiently (it was just a simple piece of reinforcing). G's comprehensive method will go on 'file', like many other useful threads!