Flooring Tile - subfloor for tile

I am in the process of renovating my 2nd floor bathroom.

It originally had a tile floor with a 2-3 inches of concrete underneath.

I tore up the old tile and all the concrete to expose the floor joists and subfloor.

The floor joists were beveled on the tops for some reason...so the tops of the joists look like an upside down "V".

I want to put new tile down but I'm not sure if I should rebuild the subfloor with sister joists, 3/4" plywood and then 1/4" concrete backerboard.

Or should I just leave the floor as-is, and pour new concrete and then tile on top of that?

Thanks!

Hi!

It's not as simple as pouring concrete. It's actally packed mud, and takes some skill. Your best option would be to sister those joists, add new plywood, then your backboard.

Can I use self-leveling concrete instead of packed mud? And then just tile over the concrete?

Thanks

Nope. Can't be doing that. A mud job is typically at least 2" thick and self leveling cement cannot be poured that thick, and it would be VERY expensive.

One question. You "exposed" the subflooring, right? How did you expose the floor joists without removing the subflooring? I believe what you have are screed stops for the depth of the packed mud. You don't have to use a packed mud floor, as Mark said. Re do the subflooring, add cbu and install the tile.

Never said he had to mud the floor. ;)

I was going by the comment, "removed 2-3" of concrete. I agree, it would seem cbu would be sufficient, but I was curious as to what was uncovered.

Years ago, they must have liked the approach to do thick mud pours as a base for tile. I have had to chisel up deep mud pours when removing the tiled flooring in front of fireplaces, in the same way. I remember saying to myself, "WHAT in the world!"

A properly installed mud floor is far superior then any cement board or membrane IMO. Just hard to find a skilled tile setter that knows how to do it.

Thanks guys...after removing the "mud", I was left with the floor joists with planks toe-nailed between them.

I made some offical measurements yesterday. The problem is, the floor joists are only 1.25 inches below the hallway floor...while the planks between the joists are 2.25 inches below the hallway floor.

So I guess I will install 3/4" pywood, and then 1/4" cbu. With the tile and thinset above those, I might come out even with the hallway.

Thanks

OK, I see, now. All you had was a mud pan for the concrete. Although it may raise your tile above the adjacent floor a little, I would opt for doubling your subflooring, then adding the cbu. It is far better to have a solid floor and transition to the adjacent room.

Chandler,

When you say double my subfloor, do you mean use 2 sheets of 3/4" plywood then 1/4" of cbu?

Thank you

Yep. Two layers would be 1 1/2", add the cbu, you are up to 1 3/4 (+). Add your tile and thinset, you are looking a little over 2 1/4", which may hit it right on the head.