help with fibreglass moulds req

[gavsgonefishing]

Need a little help

I had to destroy the gunnel mould ( ply painted with 2 pac primer) because the glass did not release as it should.

I have also had dramas another mould (taken from the original gelcoat) yet on the same day I made a mould up on the side of the hiull, no dramas, popped of beautifully.

Differences with the moulds:

The first one was ply and waxed up over a week ago (7 coats of wax)

Second one and third one was waxed up on the same day but six coats as it was a once off mould.

The second mould was a single 600gram, the third mould was 2 x 450 gram.

All moulds were coated with a hot brew of resin, taced off then applied another resin, glass, resin glass resin.

OK, two concerns, why, and is ply suitable for a mould, do I need to coat it with resin first before I wax it up. It takes me a week to build these things, and I have the other gunnel and back gunnel to go, so all advice with be appreciated.

The gunnel mould was used on a hot day, three layers of chop was layed, set then another three, is the heat penetrating the bottom layer of resin and then soaking through the wax into the ply

[blaze]

Hi Gav
Have you seen that 3 ply with the polished water proof surface, a bit like laminex. I use that at times. I think you may need to paint your strucual ply with 2 pack paint then apply your release agent. probabley have to let your paint cure for 10 days also as it leaches out chemicals for a few days, even though it may seem touch dry and hard it aint. probabley no help
cheers
blaze

[Kerry]

You make no mention of it but presume you are using a release agent after the wax?

First layer on mould, straight resin or gelcoat proper/

Cheers, Kerry.

[NQCairns]

Hi Gav that is a real bummer I read how much work you put into those moulds.
Here is what I have researched ready for my big pod building exercise sometime in the future. Keep in mind that you already have way more experience at this than I do.
Coat the ply with hot resin then when dry recoat to obtain a fairly smooth surface, do 4 or 5 coats of NON silicone wax like that Karuba (sp?) wax. polish well between each coat, then use a thin film of PVA (poly vinyl alcohol). The PVA is the 100% insurance policy I understand, hope the next try goes better. cheers nq

[gavsgonefishing]

Kerry, sorry terminology, I am using the release agent (7 layers). No gelcoat at this stage..

I will be using gelcoat on the extension, so I want to make sure that the mould will pop off without sticking.

I wanted to make sure that I could get the glass to pop out of the mould no dramas. This is the first time I have attempted this (apart from the bearers, which were no probs) so I did not want to introduce the gelcoat until I sort of know what I am doing.

Blaze, the ply was sanded back, with the bog, then coated with the 2 pac primer and rubbed back for a smooth finish left for a good week, then waxed up with the releasing agent (this was completed in one night and left to stand for the week, had to work unfortunately).

[gavsgonefishing]

nq cairns, that pva stuff, what is it? . Obviously the f/g shop must carry it

[NQCairns]

Gav that PVA is the release agent I think? Also I think the job is to sit for 5 or so days before pulling from the mould.
If this happens to me it will be a disaster (big mould), I plan to gelcoat in mould. good luck with it.nq

[gavsgonefishing]

A little bit more homework req I think

[gavsgonefishing]

Did a little homework today.

Is amazing how much info is floating around, all correct, but can be put together is different ways to change the correctness.

It also amazes me that you have to have a certain level of knowledge before the next level will be given. This will not be the last level as you do not know what you have to know or ask next week. It seems all trades are the same, until you speak the lingo, the info just doesn't flow....

The stuff I am about to impart will hopefully help you ask the right questions before stuffing up unintentionally.

Waxing (release agent) the mould: temp and humidity matters.eg in winter 4 coats may do, now at least 10 coats (Cairns probably 20 ;D)

Once the resin starts to go off it gets hot, now it even gets hotter, therefore penetrating the layers of release agent or ply etc.

The 2 pac paint etc is to give a smooth surface only. The only protection between the resin and the mould (glass or ply) is the release agent.

Apply the release agent , let it go off (1-5 mins), polish, let it sit for a while. Apply the next layer, dry, polish, and keep it going. Let the last layer sit over night or longer to be sure, then an hour before the glassing lay another layer of release agent on, polish and wait.

The PVA is a water based alcohol which can break down after water in applied.

It is put on the last layer of release agent, sit for an hour then you can start layingup.

This is a guarenteed way of getting that mould to free. If it doesnt, add water b/n the glass and the mould and pop(because the PVA breaks down with water). Sounds easy. Disadvantage is that it MAY not leave the gelcoat surface as smooth as you hoped ( pin holes).

2 coats of resin/ glass let it go off before adding any more coats, because of the heat transfer.

Gelcoat, its got to be about 3 business cards thick( more than0.7 mm.) you don't have to spray it on, just ONE go with a brush, no styrene. Let it go off for a couple of hrs before comencing the glassing process

And a heap more of info, but this will do for the moment

[NQCairns]

Thanks for that info, the remark about gelcoat and pva certainly got my attention I might have to chase alternatives or leave the gelcoat to brush onto the finished pod and sand sand sand oh and did I mention sand :-/. nq