GRP Moulding - The Process

[Lakesailor]

I've done lots of repairs, but not moulded anything from scratch.
Now I have a particular shape to mould. I've made a buck (is that the name?) which is the shape I want. I propose to lay-up fibreglass over it. Remove the grp shape and fair and finish that. I'm not really interested in making a mould from the lay-up. It's one-off and the extra few mm thickness in the finished product is of no matter.
How do I prepare the buck so that the grp comes away? Will ordinary spray furniture polish be good enough as a release agent?

The buck at the moment

 

[alahol2]

Can't help with the release agent but please tell us what it is... Pillow?, Fish pond?

 

[rivonia]

As long as it is shiny and well polished it will release easy.

Peter

 

[paul.norton]

I have found spray polish does not work well. Use old fashioned beeswax type.

Its "plug" by the way.

Paul

 

[Lakesailor]

Can't help with the release agent but please tell us what it is... Pillow?, Fish pond?

Oooer. Wrong forum really, but more likely to get a reply that makes sense here. It's the bonnet bulge to cover my new motor.

 

[Lakesailor]

I have found spray polish does not work well. Use old fashioned beeswax type.

Its "plug" by the way.

Paul

Good. I've got beeswax.

 

[Avocet]

Good. I've got beeswax.

Places like Glassplies in Southport or CFS sell all manner of release agents. As has been said, wax is good, but needs a good buffing until the plug is shiny. There are also various liquid release agents (PVA, I think?) that can be sprayed on. The first waxing can be quite hard work though - and they generally need several waxings before they build up their best release properties.

http://www.glasplies.co.uk/Release-Agents-s/1903.htm

I've made stuff from male plugs before, but part of the problem is that the "hairy" side will be on the outside. Are you bothered about that?

 

[prv]

part of the problem is that the "hairy" side will be on the outside. Are you bothered about that?

Should be ok with a layer or two of "tissue" over the top, then a fairly thick gelcoat.

Pete

 

[srp]

Don't use any polish with silicone in it (which means most household polishes). Proper mould release wax, 6 coats, apply, buff then wait an hour before the next coat. Then 2 coats of pva mould release, followed by another 2 coats of wax applied as before but being very careful not to damage the pva coats. That's for proper grp work, but as you're cheating by using the plug as the mould you're not going to be too bothered about the finish, so I would probably cut down on the number of coats of wax.

 

[Blueboatman]

You might want to glass a bit of core in or a couple of 'stringers' transversely avoiding the lumpy motor bits..to stop it resonating?

Better ( perhaps) use the new molding as a female mold later in the day if the mark! proves a functiional but cosmetically less-than-stunning success. Assumes of course that your plug is good enough to allow a shiny molding?

 

[Lakesailor]

..to stop it resonating?

Ha ha. The motor/box is bolted directly to the chassis. I run a straight cut gear and the exhaust is about 3 feet long. I don't think a bit of drumming will be an issue....

I plan to fill and fair the outside of the resulting moulding. For me, that seems the easiest route. It's purely to cover the motor.

 

[TQA]

Brown parcel tape over the buck works. Some wax helps but is not essential.

Make sure you know what kind of resin you have. You want to have the final coat which will be exposed to air to be FLOWCOAT. This contains a small amount of wax which prevents a sticky surface. Your build up resin should be laminating.

 

[vyv_cox]

Take some care over the glass pieces that you laminate in. It takes a lot of grinding to remove overlaps and it pays to cut the glass precisely to butt together with the adjacent one. Aim to get the layup pretty much perfect, no ridges or bubbles, using plastic scrapers, then apply the flowcoat while the layup is still 'green'. Probably not too many surfboard shapers near you but I suspect there are videos of the process on You-tube.

A common problem when doing this for the first time is to leave edges too thin. Allow a good overlap and cut back when cured.

I would use PVA release agent in addition to polishing, especially with a plug like yours that will not release easily.

 

[Lakesailor]

Ah right. Good tip on the mat layers.
I haven't ordered flow coat, so best get some now.

 

[northwind]

These guys have some good videos on their site with the basics..

http://www.ecfibreglasssupplies.co.uk/

 

[MYStargazer]

Don't use any polish with silicone in it (which means most household polishes). Proper mould release wax, 6 coats, apply, buff then wait an hour before the next coat. Then 2 coats of pva mould release, followed by another 2 coats of wax applied as before but being very careful not to damage the pva coats. That's for proper grp work, but as you're cheating by using the plug as the mould you're not going to be too bothered about the finish, so I would probably cut down on the number of coats of wax.

I've heard silicone spray works well. Doesn't it? What's wrong with silicone?

 

[Vara]

Having seen your previous automotive paint jobs, I don't think you'll be happy with the manky finish you'll get without making a mould from the plug and then producing the fairing, rough side down. Is time of the essence? I thought that the sport was only pursued in winter.

I have no idea about release agent but a quick scan of eBay would indicate that the proper stuff ain't too expensive even by my standards.

 

[Hugh Foulis]

Is time of the essence? I thought that the sport was only pursued in the winter.

Season first practice is 11 August so knowing Lakey, he will want it looking its best for then. Our first debate on this topic concluded that a washing up bowl would do the trick!

HF

 

[Avocet]

From previous experience of fibreglass hand-laid mouldings over engines, it'll probably change shape anyway (and go all ripply) once you've parked the car up with a hot engine a few times!

 

[Lakesailor]

Good point