How thick subfloor needed under tile?

Hello,

I am renovating my bathroom in a century old home ~ nothing is plumb, level, etc. After putting in all new plumbing I am ready to put the floor down. Presently, there is 3/4" plywood screwed to the joists. Despite the fact that it is a small room (6' x 6'), the plywood is down in five pieces (long story). Additional 2' x 6' and 2' x 4' boards were added to the joists for extra support.

I want to put 3/4" lime stone tiles down as flooring and someone suggested that I need to put a full sheet of 1/4 or 1/2 inch plywood down first on top of the 3/4" plywood.

What is the total thickness that I need before putting down the tile? Or is the issue not thickness but rather uniformity of movement (therefore covering over the five pieces with one full piece). Of course, it still wouldn't fully cover the floor as sheets come 4' x 8'. Do I screw the top layer of plywood just to the joists or all over? Or is it better to use an electric staple gun?

Also, where I'm using limestone as opposed to regular tile, do I need any special mortar or grout and do they cut the same using a wet saw as regular tile do?

Thanks kindly for your input!
Karen

3/4 thick ply should be thick enough, but its hard to pass judgement on the way it is layed without seeing it.

Generally just some 6mm tile underlay nailed over the top would do the trick.
If you buy the proper tile underlay it even has markings of how close to nail it. It comes in 1800x1200 sheets and has a series of ink dots 100mm apart which you can follow to nail.

If you are going straight on to ply without gluing the tile underlay get the proper underlay nails which have a ring shank so they hold better and dont vibrate loose.

I wouldnt put ply over ply unless it is pretty bad. Either way you shouldnt be sticking tiles to ply, you should use tile underlay eitherway

Andrew

Firstly if it is a bathroom , what are you doing for waterproofing ?

Stewie

It was suggested to me that I seal each tile BEFORE I lay it as the limestone is porous and the mortar/grout would stain it. I was assuming this would also be preventative for keeping moisture, etc. from infiltrating the stone. Is that sufficient for waterproofing?

Karen

Definitely not.
I'm unsure of the rules for the US or whether it varies from state to state but in Australia bathrooms are supposed to have a flexible waterproofing to the floors ( there are a few caveats to this but I won't go into this here ) returned up the walls 150mm ( 6" ) and to 1800mm ( 6' ) in showers.
I'd check your local building codes and what is required.
Tiles are then either glued to the waterproofing membrane or as is more common to allow for falls to a floor waste, laid in a sand/cement bed over the top of it.

Stewie

Thanks, I'll check out the rules regarding the waterproofing. I'm in Nova Scotia.

Cheers, and happy renos!
Karen

Hey KarenSB,

i think you should contact home renovation specialist. they will give you better advice and mostly builder of home renovation gives you free advice.