Molding fibreglass

[Foxy Smith]

I need to make up some custom air trumpets. I have the skills and technology to make up molds but I have never done any work with fibreglass. I assume it goes something like mold -> apply release agent -> paint on gel? coat -> build up tissue/resin layers to appropriate thickness. What do you use as release agent? some kind of wax?? Mold is likely to be turned from wood(pattern makers mahogany) or aluminium if I have a large enough bit in the scrap pile. Hard wax paste on timber seems to make sense to me. Regarding the tissue, I suppose it would be quite a fine grade required for this application. What colouring agents can I use? I have used acrylic paints with epoxy cements for furniture making, do they work with fibreglass resin?

 

Be grateful for any input from those who've been and done it before.

 

Ta, Alan

[thinfourth]

I have seen trumpets made with plastic pipe heated up and then shoved down onto a male mould.

 

The happy handle made me do it

[Beelzebub]

Mate of mine used to do GRP bike fairings & car bodywork. He used PVA like this stuff here

 

D.

[MorganMan]

My experience is limited to a few parts for buses and boats, but here it is for what its worth.

Assuming that you are planning a male mould to give high surface finish on inside of trumpet, fine grained wood should be OK for the mould, if you have to include a flange of some sort then careful design of the mould in this area is essential as well as careful choice of any split points. Turn, sand, and seal (3 coats of Ronseal or similar) the mould then sand again and again down to 400 grit. Ensure that the surface is sealed and grain grain closed all over, if not reseal and sand again. Preparation is essential to ensure good release. Wax the mould with bees wax, three or more coats. Paint on the selfcoloured gel coat, I would use Epoxy rather than Polyester get it from a Chandlers, add a few layers of fine mat stippling in thoroughly with Epoxy resin to expel air bubbles. Let the resin go off and thoroughly cure. Tap all round with a rubber mallet to loosen and allow air to seep btween mould and trumpet and then pull or press mould out of trumpet.

[jeff green]

Masking tape is good. You need to cover the mold carefully but dont overlapp the tape or leave gaps. The resin doesnt seem to stick. I would recommend a couple of layers.

 

Jeff