Fibreghastly

Start small next time!

Easy In Theory

After months of sanding the plug my Porsche RS60 replica inexorably made its way to the fiberglass shell stage. Given that my previous experience stopped at helping my old school chum Fastback Folster make a canoe I really should have asked the club the pros first, starting with Almac or the clever team at Carboglass. But I was impetuous…

Inside-out moldless construction meant the fibreglass lay-up had to be even. And my under-the-house workshop meant that further polyester pong would result in family strife, while a fire would spoil everyone’s day.

I turned to the interwebby. Fibreglast tutorials are a great for the inexperienced. http://www.fibreglast.com. And of course Forbes Aird “Fiberglass & Composite Materials” was my bible.

I found that an unstressed body shell needs to be light and stiff rather than strong:

Panels Of Equal Bending Stiffness

Roughly speaking a well-made fibreglass panel 2.29mm thick will be as stiff as a 1mm steel panel, but only weigh 55% as much. You can reach your own views about other materials.

Cloth reinforcements are many and varied

Basically, fiberglass threads are drawn as E-glass or higher quality S2 (aerospace but without the certification). Cloth looked like it would produce a uniform thin shell with bi-directional strength – as strong pulled one way as the other.

Unfortunately the kinks caused by weaving reduce the strength of the glass fibre ‘thread’. The fewer overs and unders in the weave the better. Common square weave is 1X1 (over and under); twill is typically 2X2 (2 over and 2 under) while satins might be 5X1 (5 harness 5 over and 1 under) or more. Thus, satins have straighter fibre, a higher glass density and are highly conformable. On the other hand they can fall apart with rough handling.

I went for 8oz (middle weight) 5 harness satin and got carried away with the sexiness of aluminium coated Texalium twill. I imported these from Soller composites http://www.solarcomposites.com. when the NZ$ was high and has them surface shipped. Soller’s service is exemplary

Epoxy matrix is readily available to home users

The simplest choice was West System, or Epiglass HT9000 from marine suppliers. There are feuds as to which is better and experts would pooh-pooh both. But they can be laid by hand – wet lay-up), cure at room temperature and won’t set your workshop alight. And they don’t pong - well no worse than a dead fish. I went for HT9000.

Epoxy creates a stronger composite than the more common polyesters, doesn’t shrink much and makes a fine glue /filler when you need a secondary bond (i.e. when you need to add an extra layer/fitting after the first layers have cured.

But take care. it is not as runny as polyester, it must be mixed in exact proportions (using special pumps) and it is poisonous. No kidding, over exposure to epoxy can lead to allergic reactions and potentially anaphylactic shock. Badly mixed and partially cured dust is about as bad.

I ruled out vacuum bagging, as I would have needed a huge plastic bag for the whole shell, a pump, etc. And I wasn’t sure that the plug would survive the squeezing.

Getting into it

“Cleanliness is a must”, said Mr. Aird. Thus I build a nice roller rack, a lovely cutting table and swept and scrubbed. About 50 litres of dust had been created in the buck stage!

“Make sure you have all your material and disposables as hand”, said Mr. Aird. Thus dozens of pottles, plastic stirrers, ad disposable brushes were purchased. I made nice steel rollers from penny washers. The picture below shows how seriously I took protective equipment.

I dry cut all the cloth panels plus some spares. Cloth makes you think of shapes and a layer plan (90^o, 45^o, 90^o).

The Texalium felt coarse. The satin felt like a silk shirt but still took the edge of scissors. A tea towel sized piece would shrink to hanky once the tension came off the fibre. Hmmm… maybe not that easy. I bargained on eight hours to knock out the front shell. Ha ha ha.

The tough bits:

• Texalium – oh dear. Being silver I couldn’t tell when it was wetted out, which lead to dry spots even with the plug first doused in epoxy. It was too coarse to follow curves while other layers tended to stand off it. One stray Texalium hair would ruin the sexy finish while the Aluminium came off with the slightest sanding. Verdict, waste of money, it’s for vacuum bagging pros only.

• Satin weave – oh dear. The material was smarter than I was. ‘Hankies’ had to be stretched and pulled to shape, which disturbed the underlying layers. Too much resin or rolling, or exuberant squeegeeing of surplus epoxy would see the satin float and pull away from the job. Stippling with a brush was the way to go. Worse, the weave was so tight that air bubbles became trapped and had to be chased to an edge or pinhole using more rolling. Verdict, leave satin alone, it’s for vacuum bagging pros only.

• Upside down – the underside of the sills and valance would just peel away from the plug in wet sticky sheets. Bang, bang, bang went the stapler in a glorious three hours before it became an epoxy stalagmite. Amazingly brown packaging tape sticks to wet epoxy and is good for holding down edges.

• Sharp edges. – cloth would not fold over a sharp edge. Laying it on the bias (45^o) helped. Wrinkles were hard to avoid and inevitably had to be flattened just as the layers cured or sanded back and patched with light cloth in a secondary bond.

• Underestimate of layers. I thought 3 to 4 layers of 8oz would do it but actually it was remarkably thin – about 1.0 mm. So in most places I used 6 layers and put any spare off cuts into the nose/tail bumper area.

• Amine blush. In humid conditions epoxies leave a waxy sheen that has to be washed off before further work is attempted. I sanded this back and wiped it with epoxy thinners #7. Actually I should have washed it as well. As a result I’ve found some delamination.

• No matter how good a secondary bond is, it’s never as good as a single piece that has chemically cured together. Actually cloth is prone to delamination anyway because it lacks the little hairs and thread that go between layers.

• Exothermic reaction – I used an oil column heater to make the epoxy runnier. Whoa, I mixed a double batch and got a runaway reaction. Hmm this resin’s getting lumpy, argh my hand is getting hot, *&%! the pottle's smoking.

I got better as I went along

• Keeping it clean -. A workshop door strip show and 20-metre underwear sprint kept the poisonous stuff it off my carpets, dinner and cat. The candifloss off my stippling brush made for a sticky mess that later became a nest of dangerously sharp porcupines. One day’s work required at least one day’s prep.

• Two pairs of hands - there is a hell of a lot of mixing of small pottles, cleaning as you go and holding two ends of a sheet at the same time.

• Bite sized – lay-up worked best when I worked on smaller parts with the plug rotated to keep the job horizontal. This meant that a part took only 2 or 3 hours to lay-up and cured as one sheet. While the parts eventually had seams that are secondary bonds they could be tapered, staggered and reinforced from below.

• Square weave - when I needed extra cloth I simply bought 6oz and 4oz square weave from marine supplier, Burnsco. It was a piece of cake. The open weave wetted out easily and air bubbles disappeared. It may not have been as strong as satin, but I was beyond caring.

• Filler - epoxy can be mixed with glue powder or filler for a fantastic patching and joining potion.

• Lateral thinking. One part can be used to shape another. I became an expert at making odd shapes from house hold items. Rubbish tins make good headlight shells!

Making Flanges

Parts Are Awaiting

This part of the job was the stickiest and most dangerous. But it was also one of the most rewarding. No kid had a better present at Xmas than I had when I visited the cured job in the morning, rapped on it with my knuckle and heard the satisfying noise of my new car body.

That I managed to build something as pretty as an RS60 eases my concern that it’s a mess of delamination, bubbles, excess resin and thin spots just wait to bite me at a later stage.

Chassis Next