Hello everyone,

I just made my first molds and attempted my first infusion which failed miserably due to an airleak. I probably should have removed the wet fabric and cleaned the resin from the mold immediately, but I didn’t. Now I have a layer of resin that has attached itself to the mold surface and has cured. For whatever reason, this resin won’t release from the gel coat. Is there a way to remove it? Or am I looking at either sanding it off and repolishing it/ tossing it and rebuilding the entire mold?

The mold was made from fiberglass and polyester resin & polyester gelcoat.

The mold release was multiple coats of Mequires mirror glaze #8 paste wax AND a thorough coating of pva.

The resin system was an epoxy infusion resin from a dealer in the USA.

Learning lots here and I look forward to your collective thoughts!

Hmmm, epoxy in a polyester mould with traditional release agents is a bit of a recipe for disaster... Unfortunately if it isn't coming off, there's a good chance it has bonded to the mould. I would have a good effort at getting it off, try using a high pressure washer to blast it off and if that doesn't work then try to get under it with a blade (which will scratch your mould surface, but that is easier to repair).

If it isn't coming off, then there's a good chance you will need to remake the mould. 

Thanks for your reply!

I kept getting mixed answers about the epoxy resin in a polyester mold question. Some say no. Some say yes. Some say yes /w pva... Live and learn I guess. I’ll try the pressure washer idea first. Hoping I don’t have to build a new mold since it’s 7* outside now and I don’t have a heating building to work in and polyester stinks to bad to do in the basement!

If it is a new mould and the mould surface was under cured then any material could have stuck to it. New moulds always need to be fully cured and first parts need extra care and attention.

http://www.rexco-usa.com/why-molds-stick/

Yeh you will get mixed answers because it depends a lot on the specific material you are using. For example the polyester gelcoats I have I know don't have any compability issues with epoxy, but I have used other brands in the past that would stick every time. Technically PVA should work, but it really needs to be sprayed to have any chance. If you've brushed or wiped it on, or even if you've sprayed it on too thin, and the epoxy can make contact with the polyester surface then there's always a chance it will bond.

This is something I learned the hard way too; if you are using new materials for the first time and you have any doubt at all about their compatibility - do a small test before you commit to anything. 

Epoxy in a polyester mold is definitely not a good idea. Pva can solve the problem, but the application of pva itself is already difficult enough. It isn't easy to get an even, full coverage of the mold surface. Further, the pva film can easily be damaged during the layup process.
In my opinion, pva is only still that common, due to the good old days, when there was no better option. There are still some minor cases, in wich it might be useful. But this usually involves original models, that can't be painted, and wich are of an improper material for mold making.
What you can do now: bathe the mold in warm water, to get the pva's release propertys to it's max, and then carefully try to work from the outside with a plastic sheet (some cut grp for example). Likely there will be a point, where you'll need a metal tool, to get the epoxy off, and likely you will get some chip offs in your gel coat.
What you can do in the future:
-use vinylester tooling gelcoat for polyester molds
-use epoxy tooling systems
-when using polyester molds, you can use some polyester gelcoat for your part. make sure to cover the flanges as well (except the are for the tacky tape)