Hello, I’m a homeowner with intermediate skills. I salvaged 1”x9”x17' vertical grain fir boards from the old, foldable bleachers in the high school gymnasium. They have several coats of spar varnish on the top side, only stain (and gum) on the underside. I would like to use them on a deck with a Light Gage Steel (LGS) frame. I prefer to leave the boards full width and use a hidden fastener system.
My concerns are:
Is this wood species a good choice for a deck?
Will the spar varnish on top with nothing on the bottom be a problem?
Will the 1 x 9 inch board width allow the boards to cup if only hidden-fastener-attached on the edges?
What type of hidden fastener works best?
What span should I use for joists since the boards are a full 1 inch thick?
Any other advice would also be welcome.