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Fibreglass pointers needed

sdh2903 - 5/1/13 at 05:02 PM

Hi all, its time to sort the probs out with my bodywork. First up when I joined my bonnet and nosecone together there was a groove on the upper surface approx 3/4 of an inch wide, I filled this with P40 fibreglass filler, skimmed with P38 and painted. A few weeks later cracks began to appear which can be seen in the pic below. Now i've either still got a bit of movement in the join causing it to crack or I should have used resin and matting to fill the gap? Any pointers or suggestions taken gratefully!

bonnet2

Second up, same bonnet/nosecone, i have a gap in front of my wishbone are that I would like to extend the GRP to close the gap. How would be best to do this? A piece of fibreglass sheet cut then joined with resin/matting? Excuse the crap drawing below:

bonnet

kwakkwak6 - 5/1/13 at 05:42 PM

Resin and matting would be the same as the p38 is basically shredded matting with resin mixed in . Is more than likely the p40 has not adheared properly and is floating . I use upol filler as it more rubbery and works better . When I have to put filler on top of glass I drill it with 2mm drill and apply filler the holes help it bond .

mark chandler - 5/1/13 at 05:52 PM

When you join two straight lines you get this type of issue, cut a saw tooth patten on each side then bond, the join will be across a much larger area then and the propensity to crack will diminish.

Also when your filling the curves will much easier to keep true as no straight join.

Make it worse then to make it better

Regards Mark

[Edited on 5/1/13 by mark chandler]

sdh2903 - 5/1/13 at 06:11 PM

Cheers for the tips.

Im not sure its the P38 thats cracked as there was only a tiny skim, If anything the cracks are where the P40 meets the original GRP.

Mark, having seen that method whilst searching that would be the way I would now do it, I dont think I will be able to achieve this method now without having to replace the bonnet and nose as I dont think I will get them apart now.

Charlie_Zetec - 5/1/13 at 07:00 PM

I'd fill it with a fibreglass tissue, not matting (chopped strand is the usual) as suggested above. If it's a weak part that flexes a lot, the. Consider using woven roving mat - but make sure you use epoxy resin, as opposed to polyester ("old" polyester resin doesn't like adhering to "new".

Hope that makes sense!

sdh2903 - 5/1/13 at 07:09 PM

quote:
Originally posted by Charlie_Zetec
I'd fill it with a fibreglass tissue, not matting (chopped strand is the usual) as suggested above. If it's a weak part that flexes a lot, the. Consider using woven roving mat - but make sure you use epoxy resin, as opposed to polyester ("old" polyester resin doesn't like adhering to "new".

Hope that makes sense!

Yes kind of

any recomended suppliers of materials?

sdh2903 - 5/1/13 at 08:04 PM

Going a bit further, have started to get ideas above my station now but bear with me. Would it be feasible to use my current bonnet/nose cone to make a mould and make myself a new one in one piece? I've just watched a couple of vids on youtube and looks like it might be a good little project.

What sort of quantitys of materials would you be looking at to make the mould then the final product?

Gel goat
matting (300g?)
resin (epoxy or polyester if im starting from scratch?)

cheers
steve

Fred W B - 5/1/13 at 08:53 PM

The materials add up quick, measure the surface area of the intended part. On my project I used:

Mold
Gell coat - 500 grams per m2
CSM - tissue, 1 x 300, 5 x 600 grams per m2

Part
Gell coat - 500 grams per m2
CSM - tissue, 1 x 300, 2 x 600 grams per m2

Resin - allow 2.4 kg of Resin per kg of matt.

Cheers

Fred W B

Charlie_Zetec - 5/1/13 at 10:01 PM

quote:
Originally posted by sdh2903

quote:
Originally posted by Charlie_Zetec
I'd fill it with a fibreglass tissue, not matting (chopped strand is the usual) as suggested above. If it's a weak part that flexes a lot, the. Consider using woven roving mat - but make sure you use epoxy resin, as opposed to polyester ("old" polyester resin doesn't like adhering to "new".

Hope that makes sense!

Yes kind of any recomended suppliers of materials?

I would suggest a chandlery for a general purpose kit or materials - someone who is knowledgeable should be able to assist. Probably not the cheapest place, mind....

I think trying to make your own is a very big step, and there's a lot more to it than most realise! Material costs add up at a substantial rate, and you'll end up with a big shock at the end of it.

PS - don't forget to clean the area to be prepared with acetone before you start working on it....

[Edited on 5/1/13 by Charlie_Zetec]

sdh2903 - 6/1/13 at 08:52 PM

Cheers guys, now i've sobered up, i will be repairing mine rather than making new!

I'm going to try and separate the bonnet and nose and redo the join properly, first time round it was done in a rush and only using the kits from halfords.

Only thing im a little confused about it the choice between epoxy and polyester resins. Most chopped strand matting Ive seen is for polyester and the roving woven mat is for epoxy. For my purposes which would be best? Not too fussed if the epoxy is a little more expensive, just want it done right so I dont have to do it again.

Cheers
Steve

Charlie_Zetec - 6/1/13 at 10:53 PM

quote:
Originally posted by sdh2903
Cheers guys, now i've sobered up, i will be repairing mine rather than making new!

I'm going to try and separate the bonnet and nose and redo the join properly, first time round it was done in a rush and only using the kits from halfords.

Only thing im a little confused about it the choice between epoxy and polyester resins. Most chopped strand matting Ive seen is for polyester and the roving woven mat is for epoxy. For my purposes which would be best? Not too fussed if the epoxy is a little more expensive, just want it done right so I dont have to do it again.

Cheers
Steve

Hi Steve,

You can use epoxy or polyester resins with either CSM or woven roving tissue - it really makes no difference. The woven will provide a higher tensile strength but obviously comes as a price premium to the CSM.

Both can be finished to a reasonable level on their own, but would benefit from a final tissue layer on top for better result.

As I previously mentioned, I think (99% convinced) you'll encounter adhesion issues is you try and use new polyester resin on the old polyester. I would strongly recomment you go with epoxy and woven cloth. I wouldn't like to bet my life on it, but I'm pretty sure most fibreglass layups for body panels are made with polyester resins due to cost saving and lack of necessity for epoxy.

When it comes down to doing the work, make sure the area is dust and oil free, and use acetone to clean the repair area. When you mix the epoxy resin with the hardener, be precise with your mixture ratios, otherwise if will either set too quickly or not at all - I won't go into the science of it all now unless you suffer from sleep deprivation, in which case I can kill two birds with one stone.... And to help ensure the materials stay put during the process, "dab" the resin onto the cut-to-shape cloth rather than try to brush it on (this will also help to ensure it gets right into the base and expell air trapped underneath).

Good luck!

sdh2903 - 6/1/13 at 11:21 PM

Much appreciated!