Dave M

What are the pros and cons with mat and cloth?

I'm building an engine hatch out of either coosa or plywood. I'm glassing in some ribs on the bottom of the hatch.

Which is stronger?

I've worked with mat a little, but it looks like working with cloth would be easier and less messy.

Dangerous Dave

I always figured cloth is stronger. I assume you're talking about chop strand mat. I just built race hatches for my 28 Cig using two layers of 6oz. bi axial cloth on top and one layer on the underside. I used epoxy resin and I can jump up and down on them with only a little flex. And I used 1/4 inch birch plywood. Very light and strong. I'll post some pics when I shake this hangover.

Dave M

Sounds cool DD! I'd like to see the pics.

If you are not using gelcoat and a mold what techniques can be used to make the top of the hatch smooth?

I was planning on having the top of my hatch apolstered so I wasn't too worried about how the fiberglass work looked. But, I may skip the apolstry if I can get a smooth surface on top.

Dangerous Dave

Three coats of self leveling polyurethane paint and more sanding than I care to admit. The epoxy self levels pretty good but the urethane is a challenge. If you mess with it you'll screw it up. If you did all your sanding and then sprayed a few coats that might work but airborne urethane is extremly bad for your central nervous system. I still need to do some sanding and then I'll do a clear coat but if it doesn't turn out like I want it to, I'll upholster it.

Catagory5

You can use a BPO fairing putty over the epoxy and sand using a long board. Then prime, then paint. The putty will take up any imperfections in the glass and form a good base for the primer and paint. It's also more cost effective and durable then gallons of good paint..

DD, 3 shots of 6oz over 1/4 inch ply seems a little light to me, depending on the span. You may want to consider another few shots on the bottom if the top is already painted. The flex your talking about, most likely will cause your paint to crack esp since you have it thick enough to fill the print of the fiberglass.

Dangerous Dave

Cat 5,
I agree with you about it being light but that was the way it was designed. You'll see when I post the pics. There is not much of a span. Also the flex is minimal in the weakest spot with 190 lbs jumping on it. I appriciate the input.