Thin-set or wet-bed mortar mix? [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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07-26-2011, 04:29 PM

I am renovating a bathroom in a house built in the 50's

Behind the tile is a very thick, 3/8's - 1/2" wet bed of sand and cement (it looks similar to concrete as it has little pebbles within it)

The old tile only went about 3/4ths of the way up the wall in the shower.

Because of this, when i took out the old tile, the wet bed is protruding past the rest of the wall (the 3/8ths to 1/2" i mentioned earlier).

However, i wish to install new tile all the way up the wall, not just 3/4ths of the way.

At the tile shop, the manager told me to rough up the surface of the cement board wall, put a primer on it, then put on thinset so it will become flush with the wet bed.


1. Should i use thinset to bring the upper wall flush with the wetbed? Or should I use a sand and cement wet bed mortar mix?

2. When i am smoothing out the existing wetbed, should i use thinset or a sand and cement wet bed mortar mix?



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07-26-2011, 04:39 PM
Hi Scott, welcome. What method of waterproofing do you plan to go back with?

07-26-2011, 05:09 PM
I have no idea, what should i do?

07-26-2011, 05:31 PM
Either a plastic liner over the studs before the wallboard or a SAM *Surface applied membrane" just before the tile......Kerdi, Hydroban, etc.

07-26-2011, 05:44 PM
I forgot to mention that, behind one wall there are no studs, there is a solid wall of cinderblock.

another wall also has no studs, just a sheet of cement board, then the wetbed mortar mix

07-26-2011, 07:09 PM
pictures for good measure,

let me know if you have any questions

Houston Remodeler
07-26-2011, 07:12 PM

Is the in NON wet areas or wet areas also?

I was thinking of kerdi board on the upper area for the ease and speed

07-26-2011, 07:14 PM
Scott, there are different ways to go back with it. Like Laz said, You can go back with a traditional pan liner that covers the floor and up the walls 10 to 12 inches along with CBU (cement board unit) or you can go with a surface applied membrane like Kerdi over sheetrock. You can do searches here and read up on which way you feel the most comfortable. All the methods work when installed correctly.

07-26-2011, 07:23 PM
there is wet bed everywhere, in the wet areas and in the non-wet areas

07-26-2011, 07:47 PM
It can be patched up if that's the way you want to do it. We would usually tear it all out and go back with new materials. A solid mud bed is a great surface to tile but in the shower the bottom section would need to be taken out to make room for a pan liner. Can you show a pic of the shower?

07-27-2011, 05:36 AM
but should i patch it up with thinset or should i patch it up with another wet bed mix?

Todd Stull
07-27-2011, 06:04 AM
After seeing the pics there, I've torn a few of those out... around here in Pa there was a time period where true mudset walls were strayed from and were layering some kind of plaster mix inbetween a plaster set wall and a brittle sandy/gravel mix which looks like what you have. The ones I have seen would be loose at spots, calcium deposits and very uneven... I think you should tear that doen to the studs and rebuild:clap2:

07-27-2011, 03:58 PM
I decided last night that, that is what i should do

I am tearing out the walls.

I discovered that, in fact the shower/bath area does have studs. However, the back wall might be layered as such (cinder block, cement board, wet bed)

What is the best way to remove the wet-bed on that wall without destroying the cinder block?

More pictures:

07-27-2011, 04:19 PM
Looks likes you've got a good start on it. A 3 lb hammer and some tin snips go a long way!

Be sure to use gloves and eye protection.......

07-27-2011, 05:53 PM
Scott, are you going to keep the bath tub or take it out and make a shower stall? I would take out all the old mud. An electric chipping hammer can be rented from Home Depot. You may have to experiment with the mud on the blocks to see the best way to remove it.

07-27-2011, 08:27 PM
The back wall (shown in the picture below), I am not sure if i can remove the wetbed made of concrete. It is very difficult to chip, and on top of that, it is the only wall where there are no studs behind it.

The wall is built up as follows (from inside the wall to outside):
Cinder blocks > Cement > Plaster > Wet bed/ concrete mix

I am thinking about the following options

1. attaching metal lath to the painted portion of the wall and applying mortar to make the whole wall flush and smooth

2. attaching cement board at the right thickness to the painted portion of the wall to bring it flush with the wet bed. Then attach another piece of cement board over the whole wall to have a flat surface to begin to tile over

3. Grind down and remove the existing wetbed which is right over the cinder block (I have no idea how to do this step without chiseling the wet bed every day for the next 5 months)

4. Does anybody have any other ideas. What is the proper way to do this (to make a flat surface i can tile over)??????

07-28-2011, 04:25 AM
Two options come to mind:

1) Fur out both sections of the wall and hang backerboard. This allows you to correct the difference in surface planes and has a continuous surface that will not require any special movement accomodation between the concrete block area and the drywall area. You would need a surface waterproofing membrane, or you could use plastic sheeting over the furring if you did that on the other walls and had a PVC liner under the shower floor. You lose about an inch of space, though.

2) Install metal lath over both sections and mud the wall. Again, you have a continuous surface to set the tile. You would use a surface waterproofer or hang plastic over the wall before installing the lath. You lose less space (a bit over 1/2") and mud requires some skill to apply.

You could save some space by renting a grinder or demo hammer to remove the mud and plaster from the blocks. If using the demo hammer, drive the chisel across the mud, rather than straight into it, to protect the blocks.