Water proof about everything.
1. Mineral Spirits
2. 100% clear silicone caulking.
Empty container to mix in and a stir stick.
I used about 1/4 of the silicone tube and the quart of mineral spirits. If I had more mineral spirits I would have thinned it more.
It's a hindsight thing, pour in the amount of mineral spirits then add silicon until it's almost as thick as water.
A drill with a stirrer makes it a lot easier because it takes a while to break down the caulk.
(edit) I have found that mixing the Silicon and Mineral Spirits in a plastic water bottle works best. Put in the ingredients, screw the lid on and shake. If the bottle has one of the popup drinking spouts, just open it up, squirt out a trail, then use a brush to spread it around. It will still cure in the bottle so use it or lose it.
Don't use an expensive brush, (I have found that if you work the brush as the silicon on the bristles cures, the brush will still be good for water based paints. The bristles are sealed so any paints slide right off. i have not tried oil based apints with a siliconed brush, but silicon is not paintable.
I painted the mixture on an apron as a test. It did not change the color, nor the texture of the fabric. Doesn't seem to have added any weight either.
I had plenty left over, so the 2'X4' piece of Luan I used to paint the apron got a coat as well.
It soaked in almost immediately, so i flipped it over and did the other side as well.
After curing for 2 days, i poured water on both the board and the apron.
The water beaded and ran off.
I still have about a pint left. (here kitty kitty)
Mineral spirits is not kind to all things, so make sure the material won't be harmed and have fun.
Should be good for all outdoor stuff including patio furniture.
Since the silicone soaks into the fabric and fills the voids and coats the threads, this will probably extend the life of whatever fabric you use it on.
SAFETY NOTICE! No open flames or smoking.