framingplywoodshower
I'm framing in a 40" x 16" shower bench and I plan on using 3/4" plywood.
I plan on using granite to sit on top of the seat.
I would like to know what kind of plywood I should use for the seat?
Should I use pressure treated? I've heard that pressure treated wood is not recommended to use inside the home.
What about sheathing plywood?
Take a look at these Standardized Work Table Plans as it might give you some ideas. Obviously you would not need the lower shelf, but otherwise it would be similiar (but scaled down), and this thing can hold a lot of weight!
(source: eaa1000.av.org)
I have to say that I am no fan of cordless framer nailers. I have had two different ones, a Porter Cable and a Pasload. Both were gas fired. The PC was a disaster. Had lots of problems with the propane cells seating properly and nails jamming. Got the Pasload, worked OK, but slow and the smell was so bad that I only used it outdoors. The gas cells are expensive also. After two days on a job, I went back to my trusty Bostich 88 and ran the compressor off a gen set. The other thing I hated was that it could not shoot 10d wire collated nails that I use in my other air framers. Those plastic bits flying at your face sting and you have to reload much more often. Absolutely hate plastic collated nails!
To be honest, I have not tried one of the new battery operated models yet. For framing, I like the largest, thickest nail.(3 1/4") and most cordless ones don't shoot the same larger nails I use in my Bostich.
Since your projects are at home and you already have a 135# compressor, I really think you will get a lot more nailer for the $$$ if you stick with a Bostich 88 mag or similar. You will be able to shoot 4d to 10d nails. The unit itself is much lighter, cheaper and very dependable.
For what you pay for a good cordless, you could own a good framer, 16ga finish and 18ga brad gun, thus having the right tool for every nailing job.
I have to say however, a good cordless finish gun is wicked handy and the battery models have plenty of power, but this humble carpenter is not sold on cordless framers.
Best Answer
The answer is - it depends.
If you are using Kerdi membrane plywood would be acceptable. Actually Pine sheathing plywood is the common type I have seen used for benches and steps in showers by my tile guys.
I personally wouldn't use PT plywood. PT is perfectly acceptable to use in a home but its purpose is to handle water/moisture that should be common to the situation. Basement outer wall framing is a perfect example - and bottom plates is a requirement in most areas. However I have dealt with PT dimensional lumber and plywood and there is a significant chance of warping - even if you get your stuff from a good lumber yard. If big box you have a 80% chance it warps unless you secure its shape. The point is the last thing you want is a bow in the plywood on day 4.
The lumber used to frame your shower should never get wet. So you don't need PT. And even if your shower framing got wet, that would be the very least of your worries. Meaning get quality wood but not PT.
So I would answer that this should be plastic plus plywood with kerdi membrane over or it should be hardiboard plus some sort of roll-on waterproofing like redgard (I do not plastic behind hardiboard as I feel it doesn't weep so putting plastic would cause an area that retains water that doesn't dry which will weep down and destroy whatever is below it).
Note: Make sure you slope your bench in (doesn't need to be dramatic). The back of the bench is the most vulnerable part of the whole shower. I would make sure my waterproofing is perfect there. You don't know how many benches I have seen with no slope or sloped towards the wall.