Fibreglass moulding

[gretsch-drummer]

Hi all, just started (in the very deep end) in the world of fibreglass mould making. I'm making a fibreglass bonnet for me and a mates Citroen AX hillclimb car. All went very well for my first time fibreglassing:



Gelcoat:


Glassed (I have now added more bracing over the curve):


Released:


My question now is, if I have to use body filler on a pattern/plug part, what should I use to seal if before applying the Gelcoat? Can I just finish the body filler down to 1500/2000 grit and apply the several coats of wax and PVA release?

Thanks in advance.

[Fastpedeller]

Have you experience of using PVA release? I've used it on a couple of occasions (ok. I didn't learn the lesson first time) with the result that I couldn't get the part out! I now only use wax.

[gretsch-drummer]

First time I've used everything on that bonnet. I watched the videos of that Aussie bloke on youtube for pointers (search "fibreglass bonnet" and it's at the top and "easy composites" video on the mini bonnet mould).

I first gave the bonnet a good 10 coats of wax then applied the PVA with a brush but it was separating/streaking out so I used a foam sponge applicator to wipe it over again just as it was about to dry off. It leveled out nicely over the bonnet and the release was spot on.

[Evoluzione]

gretsch-drummer said:

My question now is, if I have to use body filler on a pattern/plug part, what should I use to seal if before applying the Gelcoat? Can I just finish the body filler down to 1500/2000 grit and apply the several coats of wax and PVA release?

Thanks in advance.

The basic answer is yes. If I told you gel coat is car body filler in a slightly different form then you'd get it.
After (or if) the mould is used for multiple pulls and as your knowledge and confidence grows you realise you can leave the PVA and just use wax, but it's useful on a new mould and for a learner.

[gretsch-drummer]

Evoluzione said:

The basic answer is yes. If I told you gel coat is car body filler in a slightly different form then you'd get it.
After (or if) the mould is used for multiple pulls and as your knowledge and confidence grows you realise you can leave the PVA and just use wax, but it's useful on a new mould and for a learner.

Cheers Evo, just what I wanted to read.

What did surprise me was just how much resin you go through. With 1 layer of 300g and 2 layers of 450g plus the reinforcing bars, I used 5kg of resin.

[Evoluzione]

gretsch-drummer said:

Cheers Evo, just what I wanted to read.

What did surprise me was just how much resin you go through. With 1 layer of 300g and 2 layers of 450g plus the reinforcing bars, I used 5kg of resin.

Can I ask why you need the filler?
A ribbed roller is useful for cutting down on resin usage, basically if you put some dry CSM on top of some which is already wet, roll it and it pulls the resin though, makes the part cheaper and lighter.
Also if you can get some cheap basic coremat it builds up thickness and strength very quickly too.

[gretsch-drummer]

For the filler it was just if I wanted to make a mould of a dented panel where I'd have to fill beforehand etc.

I've got a paddle roller and a corner roller which I learnt by the end its best to use both at the same time when trying to remove the air bubbles from the bracing sections etc. But I was only using the paddle roller 'after' wetting the layer throughout, will paddle before from now on. Cheers for that tip, Evo.

I got given a big roll of this double type matting which I've not used yet. It's both woven and has a chopped mat in one. Are there any pro's and con's with this type if you've used/seen it before?

2018-01-28_11-55-33

[Evoluzione]

gretsch-drummer said:

For the filler it was just if I wanted to make a mould of a dented panel where I'd have to fill beforehand etc.

I've got a paddle roller and a corner roller which I learnt by the end its best to use both at the same time when trying to remove the air bubbles from the bracing sections etc. But I was only using the paddle roller 'after' wetting the layer throughout, will paddle before from now on. Cheers for that tip, Evo.

I got given a big roll of this double type matting which I've not used yet. It's both woven and has a chopped mat in one. Are there any pro's and con's with this type if you've used/seen it before?

2018-01-28_11-55-33

Yes it's always a good idea to perfect a panel before making a mold from it. What you'll find is that the mold will have a dull spot on it where the filler was, it doesn't really matter to anything, especially if you are doing a painted panel just for yourselves. For the most perfect of moulds we used to spray the plug with a coat of 2k gloss after any repairs.
Air bubbles are one of your biggest enemies when fibreglassing, your bonnet looks easy enough though, but just watch for them around the edge. Are you using tissue? That helps prevent them and gives a better surface finish if needed.

Sorry I don't know what that particular weave would be for, something highly specialised, looks like it might be ok for molds, lay it at 90 and 45' to each other.
We used to use woven roving as it conformed well, also when the part has hardened and shrunk the weave shows through and everyone thinks it's Carbon fibre

Have you worked out how you're going to make your bonnet? There are three basic types.
1. Make a skin and add some cross bracing for a lift off bonnet (tend to be a bit floppy)
2. Make one like the original with a front and a back frame bonded together. This is good if you want to use OE hinges and catches.
3. Was the one I liked best and that was by sandwiching coremat in between the layers of CSM or whatever. These were very light, stable and strong.

Make sure you heat shield it well on an engine....

Oh and if you're using Acetone for cleaning ditch it, it's far too pure and expensive for 'glassing. Find your local vehicle paint outlet and get a 25L drum of standard thinners, does the same job and much cheaper.

[gretsch-drummer]

For the copy I was planning on 300g chopped and 2 layers of 450g chopped matting, same as the mould and again adding bracing bars underneath. But now seeing that coremat, it looks tempting and strong.

Will I get away with 1 layer of 300g then 2mm or 3mm coremat then a top layer of 450g? Does it all consolidate as normal glass matt does?

Yeah I've got a big 25l barrel of gun wash/standard thinners. Do my own spraying as well, well that was before my 5 year old, hardly used, mint condition air compressor motor fried itself this weekend:

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Edited by gretsch-drummer on Monday 29th January 20:23

[gretsch-drummer]

Well, it turned out pretty damn good if I say so myself:

2018-02-11_03-29-28

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Released:
2018-02-11_03-30-03

Trimmed:
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2018-02-11_03-31-23

Ready to be fitted to our hillclimb project (road-going class). Aiming for sub 700kg with a 140bhp 8v TU 1400cc engine.

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