[Dan1973]

1961 bathroom getting gutted. As I pulled up the old ceramic tile flooring, I was surprised to see about 3-4" of a concrete-type material under the ceramic but over the wood subfloor. It's got some metal lath embedded in it, and is a little more crumbly than typical concrete (not quite as hard and less aggregate.)

I've put some cracks and divots in it while taking up the tiles. Can I just fill in and level it (possibly with self-leveler) and then re-tile, or should I take it all out down to the subfloor, then build up with plywood and cement board? The existing setup was obviously strong because in 59 years there was not a cracked tile or grout line, but now I'm worried I may have compromised it with my enthusiastic demolition.

 

[Nealtw]

1961 bathroom getting gutted. As I pulled up the old ceramic tile flooring, I was surprised to see about 3-4" of a concrete-type material under the ceramic but over the wood subfloor. It's got some metal lath embedded in it, and is a little more crumbly than typical concrete (not quite as hard and less aggregate.)

I've put some cracks and divots in it while taking up the tiles. Can I just fill in and level it (possibly with self-leveler) and then re-tile, or should I take it all out down to the subfloor, then build up with plywood and cement board? The existing setup was obviously strong because in 59 years there was not a cracked tile or grout line, but now I'm worried I may have compromised it with my enthusiastic demolition.

If it ain't broke :biggrin2:It is likely thicker than you think, they used to put the subfloor down flush with joists or lower when they did that.

 

[firebob]

That was the old way of doing it.
I do not do much tile work.



I would at least look into some isolation membrane.
In my part of the country those floors are not very flat and there would be issue around the toilets.

 

[Colbyt]

If you can flatten it and all else works I see no reason to tear it out.


I can tell you for a fact that it is a whole lotta work to get it out and you will most likely find the the joist tops cut off and have to sister every one of them to get a flat lay for you plywood. The other thing is sometimes it goes under the tub and sometimes it does not. I had no choice in the two I did.

 

[Dan1973]

I think I might take out any loose bits, fill with self-leveler and then put a layer of Ditra as the uncoupling membrane. I'm still knocking out the walls and tub and have some time to ponder it.

I do have a full view from below and the joists do not appear to have been notched or shortened.

 

[Nealtw]

I would just patch with thinset.

 

[Dan1973]

I would just patch with thinset.

No uncoupling membrane, or patch and then put down the membrane?

 

[Nealtw]

No uncoupling membrane, or patch and then put down the membrane?

Did the old tile need one? :biggrin2:

 

[Dan1973]

No, but the concrete under it was undisturbed and all in one piece when it was poured 59 years ago. I put a few cracks in it when some of the tiles didn't want to lift. They were really installed well and only about half popped up cleanly with my rotary hammer and a tile chisel bit. The rest I had to fight with and sometimes the concrete gave before the tile or thinset did.

 

[Nealtw]

No, but the concrete under it was undisturbed and all in one piece when it was poured 59 years ago. I put a few cracks in it when some of the tiles didn't want to lift. They were really installed well and only about half popped up cleanly with my rotary hammer and a tile chisel bit. The rest I had to fight with and sometimes the concrete gave before the tile or thinset did.

If you suspect the floor can move then you need one. You know what you have if they ever decouple. A floating tile floor? :vs_whistle:

 

[huesmann]

It's probably not concrete, but mortar. What kind of subfloor do you have? Ply, or diagonal 1x boards?

 

[Colbyt]

It's probably not concrete, but mortar. What kind of subfloor do you have? Ply, or diagonal 1x boards?

True. But there will be 2-2-1/2" of it and under it the the joist tops may very well be cut off. Click on the second image to see the joist detail.

 

[huesmann]

I know the stuff is hella thick—I just demo'd a bathroom with it a few weeks ago. I hate the stuff! Heavy AF and the dust gets everywhere. But I gotta give them that it's solid.

 

[Dan1973]

Subfloor is plywood. I know the joist tops are not cut off because I can see them in the basement and the plywood subfloor is the same level in this area as the rest of the house.

You're right, it is mortar, not concrete.

 

[huesmann]

As to your original question, I'd take the mortar, tile, and diamond mesh out, down to the plywood subfloor. Easier than trying to level off the mortar, IMO. Evaluate the plywood then—if it's too springy, you could put down another layer of ply and then your CBU. Or a good thick layer of ply and Ditra.

 

[jeffnc]

Agree with huesmann - I always take the old mortar bed out (almost always using Ditra or similar). I like working with my own substrate so I know how it was built. I feel the floor is more solid if I take out the mortar bed and add plywood. The reasons for using that old mortar bed don't really exist anymore with uncoupling membranes. If needed you can get a cheap demo hammer at Harbor Freight. But of course I use it multiple times and you might not, but it comes in handy for other things as well. Or you can do it the old fashioned way with sledge hammer and chisel.



https://www.harborfreight.com/1-18-in-sds-variable-speed-pro-rotary-hammer-kit-64288.html

 

[Dan1973]

Actually, I bought that rotary hammer last week (coupon for $69.99 so it was cheaper than its smaller cousin). I also have the Harbor Freight 38lb jackhammer from my basement french drain project, but it's overkill for this.

I like the rotary hammer, but the handle broke on the 2nd day - I guess I overtightened it and the bold snapped. Still usable, though.

Alright, I guess more dust is in my immediate future! Maybe I'll bust out the cast iron tub first so I can get under the mortar easier.

Thanks for all the opinions!

 

[Dan1973]

Finally got the tub out (had to cut into 3 pieces with a grinder because it wouldn't shatter) and now have a better look at the mortar. It's only about 1.5-2" thick and breaks up easily so it's definitely coming out. I can get the wide blade of a mattock under it and pop it right up, which is much less dusty than the demo hammer.

I'm going to put down 3/4" plywood, followed by either concrete backer or Ditra. Is it true that when I screw in the ply I should avoid the joists?

 

[jeffnc]

I'm going to put down 3/4" plywood, followed by either concrete backer or Ditra. Is it true that when I screw in the ply I should avoid the joists?

Yes. Basically (as always) pick your screw so that it has the correct overall length and the correct shank length as well. For example if you're screwing 3/4" plywood into 3/4" wood, you want a 1 1/2" screw (no longer) with a 3/4" shank. That way you don't have to worry about joists, and the wood will bind down tightly.


Also, once you've used Ditra, you will never want to go back to that nasty concrete backer again.

 

[Dan1973]

Yes, I'm looking forward to working with Ditra for the first time.

One more subfloor question - current subfloor is only 1/2" ply - is adding 3/4" on top going to be enough? Joists below are 16" on center.