Fiberglass

Anyone ever make something out of fiberglass from scratch? I need some stock tanks that will fit in an odd space and was thinking about making them out of plywood lined with fiberglass. It seems like the process is simple enough once I figure out what kind of cloth and resin i need. Does that sound feasible? Also, are 90 degree corners OK or do I have to put a radius on every corner?

I have also considered making one plywood mold and making them entirely out of fiberglass but I figured if I left it in the plywood shell I wouldn't have to worry about them breaking or cracking as much.

Rounded corners will be better. The plywood exterior may help protect from stock abuse

Try some Boatbuilding sites for information on cloth,mat and resin.

Egon

Like Ergon said, round the corners. Otherwise that's where cracks will start.

About 20 years ago I built a darkroom sink from 3/4 ply and lined it with glass cloth and polyester resin. Worked very well all the time I used it.

Some glass layup is made with epoxy resin, others with polyester. I used polyester because I already had the resin and hardener.

Don't know if epoxy or polyester would be best for your application.

I found a type of polyester resin that is FDA approved for food handling so that is what I will use. I am thinking about using plumbers putty to round the corners. Modeling clay would work too but is a lot more expensive and harder to find.

Did you do anything to seal your plywood before applying the resin or did you just go straight on top?

You could, depending on shape desired, radius the corners with cove molding. Tack it in place and glass over it.

I didn't do any prep to the plywood. Spray the wood with 3M 77 spray adhesive and use that to hold the cloth in place. Then apply your resin. It may be difficult to apply the resin without dragging the cloth all over the place with the resin brush. Don't have any advice for that other than crossing your fingers. 'Cause that makes it hard to hold the brush, maybe that's part of the problem?

I've seen them make dune buggy bodys with glass. They spray a gelcoat into a mold, then spray on chopped glass fiber. They also use a glass mat product that's about 1" thick before the resin wets it down.

Zuiko, buy Allan Viates book on fiberglass boat repair. Probably available used.
Polyester resin is eaisier to use but requires more stable temperature and is intolerant
to moisture during application. Set up time can be managed by amount of hardner. Epoxy is stronger and more$.
Resin is available as laminating and finish. Laminating has much less wax and succesive
layers can be added without sanding. Wash the plywood with Acetone and apply resin to the plywood first to get
good adherance. Use resin mixed with cabosil to fill and round the corners.
After it has set, apply well wetted mat. Don't lay up more than five layers at one time or it will get to hot.
Wear a respirator. Don't generate arcs or sparks. keep the area well ventilated.

Buy the book!

Polyester resin will eventually allow water to penetrate. Epoxy won't. I've used products from Raka (link below) and have been pleased with their performance and the price seemed reasonable. Other epoxy systems are available.
If you can create a radius on the corners it will be much easier to work your matting over it smoothly. I'm not an expert but have built a 16' jon boat from plywood encased in epoxy with white oak framing. Some dense woods such as white oak are difficult to fiberglass over because the wood doesn't soak up the resin very well. My experience with plywood has been good. There's a lot of trial and error involved with learning your pot-life time on your resin, etc. Good luck with your project. Whichever you use, polyester or epoxy, will need protection from UV for long term stability.
http://www.raka.com/index.html