Releasing fibreglass from the mould, any tips?

[Al Weyman]

Anyone got any info on best way how to remove the finished article from the mould because last time I did it and I used the proper release agent I nearly had to destroy the mould to get the thing out. I was using the blue release agent should I use anything else as well like bees wax?

[thebear]

Are you sure you have enough draft in the mold?

A lot depends upon your part's configuration.

You didn't state what material you are molding.

It is very hard to advise without more specific information.

[Al Weyman]

Just ordinary glass fibre on top of a white gel coat, nothing special, its a spoiler in fact. Whats draft?

[flavorPacket]

Originally Posted by Al Weyman

Whats draft?

Houston, we have a problem...

[Speedy1]

Waiting long enough for the part to completely cure has always been my short coming.
After a few days if it still won't pop, we use several thin pieces of polycarbonite plastic strips forced carefully between the part and mould.
I've seen a local boat builder use water pressure and air pressure to help things along. In his case the mould was pre plumbed so the water or air applied pressure in the deepest area of the shape.

[dtype38]

Al, after you've slip waxed (from your fibreglass supplier) and polished the mould (five to six coats with a hour between is recommended) and put the blue release stuff on, then you need another couple of layers of slip wax, polishing in between, being VERY careful not to tear the flim of blue release stuff. These coats stop the gel from eating into the blue stuff and preventing the release.
Ken

[GORDON STREETER]

All depends on the shape of the article. Should be ok if you have a good radius on any corners. Use wax and a pva release agent.

[zefarelly]

draft

1: a cold windy feeling up yer trouser leg, popular amongsts fans of old houses

2: a tapering angle used in moulding processes to allow release of work from mould, may vary from 1 to 5 degrees , its used in terracotta moulding, metal moulding/casting, and obviously GRP production, unless you have a bolt together piece part mould?

[Al Weyman]

Oh well I have no draft then in that case, overdraught maybe? Its a reasonably simple mould which I have just repaired after damaging it last time I used it.

So what you are saying D-type I use the wax AND the blue release agent, I only used the agent before so I will get some of the wax and give that a go. Someone also told me he pulls the cast product out while it still has not quite gone off, anyone tried this?

[ben240z]

Al, polish the mould to within an inch of it,s life. The more shine you can get on the mould then the easier it will be to remove from the mould and the better the finish will be on the part. With a half dozen coats of good wax, either a car wax of good furniture wax ( I have used both at different times and achieved good results with both) then carefully put in a layer of PVA with a sponge making sure that you get into all the corners, allow that to dry then you can lay in the gel coat and carry on as normal. I have in the past eased the part loose in the mould while it is still green and then allowed it to sit in the mould overnight to cure. Hope this helps. ben

[Al Weyman]

tHANKS i WILL TRY THAT, ANOTHER THING FOR A RACE WEIGHT SPOILER HOW MANY LAYERS OF MATTING DO YOU THINK i SHOULD USE AS IT CAME OUT A BIT THICK LAST TIME. (sorry to shout).

[zefarelly]

23

[dtype38]

Al, I got this method from a local fibreglass molding maker and he does this for his living:

Wax, highly polish, wait an hour x 6
Blue PVA release agent thin coat making sure no puddles or smearing
Wax, highly polish, wait an hour x 2

This seals the PVA between the two impervious wax layers and should peel apart easily... but if it doesn't get a small gap going at an edge, then pour a bit of warm water in it. That'll dissolve the PVA and make it separate much easier. I made my whole bonnet like that and it came out without too much bother.

Oh, if you aren't using specially formulated slip wax, then beeswax is the next best (bit harder to spread and polish though). If you use anything else its very important it contains absolutely no silicon. If it does you'll have serious trouble getting them apart.

Also, make sure it's cured well (at least a couple of days, but preferably a week if you have time). If you don't the moulding can distort afterwards. Also, the thinner you make your moulding, the easier it will be to remove because if it can flex it'll peel off the mould much better.

As for thickness, The main bulk of my bonnet is two layers of Gel coat and two layers of medium weight mat. I have three layers for the front of the nose and all the way round the edge. At the two front mount points and the two rear catch points there is an extra layer with aly plates sandwiched inside to take spread the mounting loads. The air dam under the nose is four layers. Dunno how that helps with spoilers, but it might.

The whole thing stays in shape at 125mph+

[Al Weyman]

Helps a lot thanxs, if I cock up now then its only me to blame. The two coats of gel and two of matting sounds about right, I think I gave it one of gel and threeof matting before and it was a bit thick. DO I let it go off between the coats of gel or just go for it?

[dtype38]

Let it firm up after the first coat of gel. Test it with your finger, it should take a print and feel very slightly tacky, but your finger shouldn't sink in (don't let it go hard or you'll need to key it up again). Then just brush on the second coat. Then get it to the same state and go for the mat. Brush a liberal coat of resin onto the gel then lay up. Two layers can usually be done straight on after the other, but if you have a large area or "overhangs" then you can simply do the same as for the gel coats and allow each layer to stiffen up a bit before continuing. Good luck.