So, I’ve laid up two of the four quarters of my composite fuel tank mould. It’s a simple layup of gel-coat, and then three layers of 450gsm chopped strand mat, set in polyester resin. Nowt flash.
Since I’ve done the first half and the second half mated to it, I’ve learned a couple of lessons:
- cut a lot of cloth to templates to fit the major areas – handy that I had the spare flanges from the first mould-part to size the cloth – this wasn’t an option when the first flange went in.
- run at 1% to 1.5% catalyst – The gel-coat needs to form a chemical bond to the resin in the backing layers, and that is done with the exothermic reaction when the resin goes off. In the first mould-part I found the exotherm was kicking in before the final layer went down. This meant that the fibres were setting whilst sticking up and making lumps. lumps mean bubbles, gaps and bridging. With the second mould-part, I used the bare minimum of catalyst and the exotherm only really kicked in as I was putting the last piece on. This is perfect and gives the gel a good baking. Each mould-part needed about 2.2kg of resin.
- don’t leave any spiky bits after a layer is finished – it just makes it worse the next layer. See above. Roller them carefully flat.
- Apply only one layer of gel-coat. Again, mixed with minimum catalyst in order to get it on once without gelling. I have other jobs to get done so I wasn’t watching the gel-coat go off. Experts spray this on and bank on about 0.4mm of gel-coat. Painting this on means 1-3 mm. However, that gives me plenty to polish into.
- Don’t try and paint gel-coat on if it starts to gel in the pot. scrap and mix more. my previous attempt with gel-coat did go a little lumpy, making the lumps and bumps worse – see 3 above
Here are the ‘bad one, then good one’ pictures:
Finally, here is the part with both flanges in place.