Hi all,

I'm just starting down the route of building a large oven for use of prepregs etc but for the time being I need to epoxy wet lay projects such as this and for that matter I'm not sure I would even be able to get hold of a low temp cure prepreg from the materials I need to use.

The project is small sidecar fairing much like an F2 Racing Sidecar only a kart sized one that is raced on kart tracks. Its about 1.5m long and has a fair amount of shape. Top end speeds are 60-70mph on larger kart circuits. There tends to be a some body contact and your average polyester/gelcoat fairing tends to look crap after only a few meetings due to the cracking nature of the gelcoat as the bodywork flexes and takes knocks from the other tricycle bumper cars! 

The bodywork needs to have some flex and 'give' at the extremities whilst being fairly sturdy around the middle part and mounting points. I guess the nearest other subject would be a white water racing kayak or similar. I will achieve this by use of multiple materials (Glass, Diolen, Carbon) where appropriate. I know I cant expect something that gets abused like this to look great forever or last forever but keeping it looking fresh for as long as possible would be preferable.

Sorry if that was all a bit long winded but once people have quizzed me about my intended use I would have ended up writing it all in the end anyway.

So...... I want a black surface finish, dont want to paint it and dont want carbon on the outer skin (looks great but is dangerous in a heavy accident). First thought it to use black Diolen for an all over first ply. I will never get this layup to stay down everywhere so will bag it, being a fairly big job I know that I'll end up with dry bits/air bubbles here and there no matter how careful I am partly due to not being able to get a coat of resin to stay on the released mould first. I have some GC50 epoxy compatible clear gelcoat but after doing some tests I'm sure it will de-laminate/crack after some impacts.

Next thoughts are to use fumed silica to spray some thickened resin onto the mould surface as a thin epoxy gelcoat which will most likely end up looking milky? Then I'm thinking maybe just add black pigment as well as the silica or will this go grey rather than black?

Any got any experience with this or have any thoughts or ideas how else I could achieve a decent looking but hardy  black surface on my mobile battering ram?



My mould and pattern

I keep a layer of kevlar inside any body panel exposed to damage. It ensures that even carastrophically cracked piece would not separate into multiple sections (makes field repairs easier).

To re-iterate what I mentioned earlier - with a cone/cupped shape like that, any laminate structure based on a fabric will be extremely strong, because of geometry (any "push" into it causes most fibers to be excersized in elongation direction). If you would like to have flexibility in there, I would try non-directional fiberglass chop in a flexible epoxy matrix, or some sort of polyurethane cast. Anything based on a woven fabric will be very stiff in that section.

Make a mini-mold in 1:4 scale for that area and experiment with simple layups, you will see what I mean.

Don't mind that other thread, they have some sort of process/contamination/material issue. I have seen more complicated shapes done with hand layup with no problems