fibreglass

[garryb59]

I'm looking at having a go at making a fibreglass seat for my recumbent bike. Apart from the odd patch repair decades ago on a car, I've not done anything with fibreglass, so I'm spending a bit of time trying to get the subject a bit 'sussed'. But I have a question that I cannot seem to get an answer for. Most fibreglass I see advertised, as well as the differing styles [like chopped strand mat, and woven] is described as having a value of 300gm/MtrSqr, for exampke, but there is a guy advertising some as having a value of 'p6'. Has anybody got any idea what 'p6' means? He says that he uses p2 and p6, with p2 being a finishing cloth and the p6 tougher, but I've no idea how it compares to the other value methods [like 300gm/MtrSqr] used to describe fibreglass.

Any ideas

Many thanks Garry

[Andy Dingley]

Try to find a copy of "The Gougeon Brothers on Boatbuilding" It's the best guide to epoxies, lamination and GRP work that I've found.

I've never heard of "p2" or "p6", but the numbers are about right for the oz/yard measures that the Yanks use.

Avoid chopped strand, pay the extra for a woven material. Use the right woven material too, if you're forming a compound curve, get something with a weave that drapes properly.

Use a gel coat, don't just slap the same resin into every coat. Use the right gel coat additives for whether you're working off a mould, or curing in the open air.

Vacuum bagging is quite easy to arrange and gives lighter and stronger laminations.

Avoid Kevlar and carbon. Carbon is a pig to work with and neither will give better results than glass, unless your technique is sophisticated.

Barrier cream _and_ disposable gloves avoids a lot of skin trouble - especially if you're using epoxy.

[garryb59]

More specifically, this is what I'm refering to. I did email the guy, but he just said what I mentioned earlier about the different strengths, and I couldn't seem to get much further.

need to mnake a mold first anyway, so I don't mind wasting a bit here and there.

Ok, this I'm yet to understand at this early stage. I was of a mind that for something where appearance is of little significance [at this stage anyway] I only really need to worry about the cloth and polyester resin? Is a gel coat not a finishing coat only? To begin with I'm only interested in a seat that holds up, it will have a closed cell foam cover anyway.

And for me, it will mean working outdoors too.

Thanks for the reply Andy.

Garry

[Rob Morley]

They are different weaves - the appendix in this document has a bit about it

[Andy Luckman (AJL Electronics)]

The gel coat stage is important. It not only gives a smooth surface, but allows the resin to set properly against the mould. After the gel coat (which you can pigment if you like) has hardened, recoat with layup resin and lay a sheet of matting. Stipple resin in (don't brush) until the colour is uniform and there are no dry spots. Lay another one in the same fashion at 90 degrees to the first and then use a split washer roller to force any air out. You could continue building the thickness, but if you aren't very experienced, I would suggest waiting for the first ones to harden off. Don't forget to polish your mould before gelcoating, unless you want to incorporate it!

Whatever you do, don't buy the "repair kits". They are identifiable by the red paste hardener and go off like a rocket. You need time, so get some pro standard material. Hardening time about an hour gives time to be happy with your work before setting.

< Is a gel coat not a finishing coat only? To begin

You *could* finish with a flowcoat, but to be honest, that may be overkill for your application.

[The Natural Philosopher]

If yiou are just doing a rough sort of job, and its a one off, you can forget most of what is 'good practice' in getting mirror finishes on production items.

If UI wabnted to make a glass bibre seat that was to be covered in foam I;d do this.

Get a pile of bulders sand.

Sit down in it. Thats yer mould. If being clever I'd add some cement and water before I sat sdwon, and sit on a sheet of polythene.

Now lay up on the polythene, the only important thing being to not have too many air bubbls. Unless v high strength to wweight required, I'd use chopped strand as its cheap.

When finshed, remove rough edges with a diamond cuitter ort other abrasive, and stiffen up where floppy with any kind of bulk embedded in firther layers to make 'hollow spars' - or just suse more strand.