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Fibreglass mould help
corrado vr6 - 22/9/24 at 09:51 PM

Hi

I am making a fibreglass bonnet for my Jago geep project, I have made a mould and now I need to make the actual bonnet. Sadly when releasing the mould the PVA didn’t release everywhere so I ended up damaging my mould. I have cleaned it up filled any holes with 2k body filler and sprayed in grey filler primer. I have guide coated and rubbed the primer down using 400 and 600 wet and dry. However in a few areas I have gone through to either the gel coat or the filler of my mould. My plan was to spray the mould in Halfords gloss white paint and then flat and polish ready for PVA.

Do I need to apply the gloss white paint or could I go straight on with the PVA? The final piece will be sprayed with the rest of the car so any small imperfections are not an issue.

Just worried about the resin sticking to the filler 🤷‍♂️

Thanks in advance

https://www.dropbox.com/scl/fi/b7ijj3653y5lo2yaybtn7/Photo-22-09-2024-22-48-14.jpg?rlkey=snr1b00grnbe3wy68w416a22w&dl=0

https://www.dropbox.com/scl/fi/mau156ms0hk07eo59sd7s/Photo-19-09-2024-14-29-51.jpg?rlkey=v2wdvsrcpop0h5henk69u79li&dl=0

https://www.dropbox.com/scl/fi/r05xy40mjyui5csi0wntp/Photo-19-09-2024-16-52-27.jpg?rlkey=5chvy6thx2rjkelhrm0kz8cq3&dl=0

cliftyhanger - 23/9/24 at 05:56 AM

Just checking as it is an easy mistake, but you did use poly vinyl alcohol, which is VERY different to PVA glue?

How about a release wax? It seems there are special release waxes for new moulds.

https://www.ecfibreglasssupplies.co.uk/tr-wax

Sarah - 23/9/24 at 10:20 AM

Use glossiest paint then polish to highest possible standard, then use wax/release agents etc.
CSF f/glass supplies has good info (like ec mentioned above)

corrado vr6 - 23/9/24 at 07:46 PM

quote:
Originally posted by cliftyhanger
Just checking as it is an easy mistake, but you did use poly vinyl alcohol, which is VERY different to PVA glue?

How about a release wax? It seems there are special release waxes for new moulds.

https://www.ecfibreglasssupplies.co.uk/tr-wax


Thanks for your reply, yes positive it was PVA release agent I had already made pieces before using the same bottle and this mould I am making was made in two halves so I can get the final piece out, annoyingly the left piece came off lovely but the right side not so 🤦‍♂️. Maybe I didn’t apply enough PVA on the right side.

I have read about people applying wax and then PVA over the top of the wax as a back up. The PVA was bought from ecfibreglass supplies as well

Mr Whippy - 24/9/24 at 11:14 AM

Although not to do with mould. I'd suggest using glass rope when you laying up to add some ribs to the inside of the bonnet and make it more rigid.

computid - 24/9/24 at 08:57 PM

Can I ask why you chose to use body filler and paint to repair it? Gelcoat mixed with Wax Additive Solution will harden on the surface and allow for a proper gel coat repair. You can then sand and polish. CR1 Easy-Lease from EasyComposites is a really good release agent in my experience. I've made quite a few moulds with it in the last few years and never had a failure.

I would personally never paint a mould, but since you have now with a primer I would definitely apply something you can polish smooth. It's always better to fix the mould than fix the part in my opinion. If you can apply a top coat thats non-porous, polish it smooth, and then apply some good quality wax in multiple layers you should hopefully get a decent release. Just make sure whatever you paint it with doesn't react with the gelcoat/resin/primer.