Making a custom fiberglass seat

I suffered a number of illusions at the start of this project, most have been shattered. The chief illusion was that I could build a seat for less than I could buy one. When all is done, this seat will cost about $100.00 more than a similar type seat can be purchased for. My guess for labor is about 30hrs when complete including seat foam and cover. The one belief that stands is you can make a seat that is exactly what you want (or very close to it.) and it will fit like it was made for your SR.

I started by making the seat mount plate from alloy, it uses the factory mounts. Using polystyrene foam I attached strips and blocks of foam to the mount plate using spray contact adhesive and shaped with a hot knife and sandpaper until I had what I wanted. I covered the foam with reinforced packaging tape because the foam was so flimsy when shaped to final dimensions that it would not consistently maintain position and shape. I tape the interior first then sanded more on the exterior to thin further. I made the sides and front slightly longer than needed to offer a final trim to size after glassing and built a stand to support the form during the glassing process.







I built up 7 layers of 9 oz glass using an epoxy resin system and learned the hard way that not all glass is equal. The only glass to use for a project like this is a 2 x 2 twill weave. It has excellent form following capability, all other glass type including very light 3 oz glass will not lay flat to the form and leave air bubbles that weaken the structure and require additional labor to deal with. With each layup series (I did 2 layers at a time, then one final layer) it is necessary to sand the form to smooth out high spots.





After the final layer is hard and sanded, (I should note here that all sanding to this point was done with 60 or 80 grit paper.) I put on two coats of an epoxy/microsphere mixture, sanding between coats to fill the weave and then a final brushed on coat of epoxy and sanded again. (In these fill coats is where I transitioned from course paper to a final sanding with 220 grit in preparation for paint).



I used acetone initially to dissolve the foam from the form and strip the tape. It worked, but not well. I switch to xylene (replacement for toluene in the US) and it worked great. (Messy bit of work by the way) After that it was trim to final shape and the usual paint work. I still need to attach the fiberglass to the alloy plate and finish the seat foam and cover. The seat cover style will be similar to Marlon’s seat cover with attaching snaps.







Mistakes I made in hindsight:
1. Believing it would be easy.
2. Not using 2 x 2 twill cloth at the start
3. The seat has raised sections along the sides of the seat for added strength. They are unneeded, complicate fitting the seat foam and I suspect I will be able to feel them through the seat foam on completion. Flat with a large radius transition to the edge is better.
4. Symmetricity from centerline is close, but not perfect. I considered making cardboard cutouts to help in shaping, if I had a "do-over" I would add this step.

What I like:
1. This is very close to what I wanted and the fit is near perfect.
2. 7 layers of fiberglass is very strong, stiff and light weight (17 oz without the mount plate, seat foam and cover)

If you have any questions feel free to ask.
Regards,
PC