Retiling an old tile floor (what to do with the mortar bed?) [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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06-21-2003, 06:02 PM
I have 2 bathrooms which I am rebuilding, and in removing the tile from the first, the mortar bed was really loose and came up in a very uneven fashion, with high spots and low spots. Also, there is an alcove off the bathroom that had settled, and there was a crack across the entrance, and the floor in the alcove was not level with the main area floor. So, at this point, I have chipped the mortar bed down to roughly even with the original joists (1930ish era floor). I can take the rest of the floor out, and put plywood and CBU, then thinset, or would I be better off just putting SLC down? What about if I want to put radiant heat in the floor? What's the best way to improve my chances of not having the floor crack in the same spot if the house continues to settle? Picture shows the current mortar bed, with the alcove towards the back. Note, I also have a gas pipe and radiator pipes to cut off and cap, so I will probably have to completely remove the mortar around them no matter what.

In the second bathroom, the thinset seperated pretty well from the mortar bed, except some parts took up chunks of mortar at least 2" thick. The problem here is that we will be expanding the bathroom into the bedroom, and will be removing hardwood floor there. Should I completely remove the mortar bed in this second bathroom, then go the plywood/CBU/thinset route, making sure the joists are level after removing the hardwood from the bedroom area? Same radiant heat issue as the other bathroom.

I have tried doing a search on the web, but no luck. Seems everybody has the fortune of tearing out plywood instead of mortar bed.



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Rob Z
06-21-2003, 08:48 PM
Hi Andrew

What you are dealing with is the main kind of job that I do. I would take all the mud out, along with the cleats and 1xs underneath the mud. The plumbers :bang: usually hacked apart the joists and the tile setters hatcheted the tops of the joists :mad: back in those days....time to get all of the mud out and scab 2x lumber on the sides of the joists and add plenty of blocking to strenghten things up before going back in with a new plywood subfloor.

Also, take advantage of the access to cut out and replace the 2" galvanized pipes that are likely clogged with crud and also knock the toilet flange off and replace it.

I would not try to resurface what you have now with SLC.

06-22-2003, 05:35 AM
That's similar to what I was thinking. I haven't seen the joists yet, but looking at what has been done to the lumber in the walls, I wouldn't be surprised if the joists are in bad shape. I did get a chunk in the second bathroom up yesterday down to the subfloor. That mortar bed is about 3" thick, although right next to the solid mortar chunk, there was small wallboard scraps embedded in the mortar. I guess the motto was/is, "Got trash? Toss it in the wall or mortar bed."

I was planning on replumbing the supply lines in the house, I'll probably replace some of the waste lines, too. I have to reroute the stack vent anyways, so that I can get the ceiling in the master bath to full height.

Thanks for the advice.


John Bridge
06-22-2003, 03:11 PM
Okay, just don't anybody try to tell me they used to build better houses back in the good old days. :D

Welcome aboard, Andrew. Sounds like you're getting good advice. :)

06-22-2003, 03:19 PM
Andrew, I'll second Rob Z's suggestion. Tear it all out and redo, it's not that bad, just dusty, and you'll know what you're dealing with. Plus, replacing those clogged old pipes with new copper will really give your water flow a huge boost I'll bet, especially if you run new supply risers.

Hopefully you won't find too much creative hacking has been done to the joists and can sister extra 2x's in for support. Have fun making a mess! ;)

06-22-2003, 08:22 PM
Well, I removed the mortar bed from the two bathrooms today. Went fairly quickly, much more quickly than taking down the plaster walls and ceiling, and cleaning up the insulation. Chipping guns are good for these things. Next is doing the rough in for new plumbing, changing a couple waste pipes, then putting in a new subfloor.

Thanks for the advice.


John Bridge
06-23-2003, 06:11 AM
Keep us posted, Andrew. :)

05-07-2004, 02:00 PM
Well, following up on John's "keep us posted" comment, I have finally gotten back to working on this bath.

To recap the progress that has occured since last fall, we can basically say: None.

There is now all new supply and waste lines, which is a good thing when I saw how much gunk was in the drain and the vent. Original tub, since finding a deep, 5 1/2' cast iron tub that costs less than $1k is difficult, and then you have to carry the new one up the steps. New electrical, new vent fan, A/C (done last summer), and now some steps completed for the installation of hydronic in-floor heating. Went with hydronic over mat because it will be the sole heat source for the room, and I wanted to tie it in to the heating plant.

So the things to do this weekend if I get the vent ducting done and isolation of the soffit vent above the bath is installation of the CBU on the walls. If I can't find hot dipped roofing nails, are electroplated sufficient, or should I resort to the expensive CBU screws?

Second question, the old tub is basically a drop in tub, in that the top edge is rolled down on all four sides, so that there is no lip on the back and sides to contain water that might get through the tile. Should I just bring the CBU down to within 1/8" and silicone caulk the joint? A related question, what should I use to clean the old caulk from the tub rim?

Now, for the big question. To help get enough heat out of the floor, I am installing aluminum plates to spread the heat out, with plywood sleepers in between the tubes. This layer will be even with the hardwood floor in the adjoining hallway. There is also plywood fill between the joists to make sure that the plates stay in contact with the sleepers. So, I will have alternating rows of 6" of plywood and 3/4" or so of aluminum. I was planning on putting CBU on top of this and then tiling (1" hex) over that. The plywood sleepers will be running perpendicular to the joists, with the widest joist space now 13" or so. Some of the spaces are on the order of 8". Joist span is fine, we're somewhere in the L/400 range.

I also have a question about what I should do in going through the opening towards the top of the picture, which leads to a little alcove in the bath. The main floor joists stop at the near side of the alcove, a doubled up joist, some space, another doubled up joist, and then a couple of joist bays running perpendicular to the joists in the rest of the bath. I'll try to get some more pictures up after I get home and can get some new ones, which show the new plywood between the joists. But a pic showing the area (behind the can), the joists I had to sister, and the edge of the tub is included below.


John Bridge
05-08-2004, 08:00 AM
You mean you'll have a layer of plywood, then your heating things in between your strips of plywood, then backer board. Should work. :)

Do what you have to do on the floor to make everything stiff. Can't see what you mean there.

05-10-2004, 09:23 PM
John, you basically have it right, except that my lowest layer of plywood is not continuous, it is set between the joists, as shown below.

The floor is quite stiff. I jumped up and down on it, and I felt no movement, and it passed the deflectometer.

My main concern is that I will have heating tubing running around the room on top of what is pictured below, with plywood sleepers between the tubes. Then cement board on top of that. So there will be some small gaps for the cement board to bridge. See for the Thermofin U method, except in my case, change the hardwood in the picture to cement board, and change the continuous subfloor to short pieces on nailers between the joists.

05-10-2004, 09:29 PM
This is related to the final question in my previous long post. What to do at the threshold to the alcove. The previous tile floor cracked across this threshold. This threshold leads to a small gabled extension sticking out of the front of the house. There is a steel plate down under those 2x sleepers, and a brick on the right edge. And the level of the original lumber is lower than the new sleepers. Should I pour this with SLC, topping mix, something else to level it out? Do I need to include an expansion joint? The main part of the bath is only 7' long, and the alcove is 3' deep.



07-13-2004, 11:28 AM
Any comments on the questions in the last two posts, the first regarding the subfloor construction in general, with sleepers and plywood set flush to the top of the joists, then ThermoFin w/plywood sleepers, then 1/4" CBU. The second question is whether or not I need an expansion joint between the main bath and the alcove or not.

Thirdly, for a bath that the kids will share, should I put some waterproofing down in the floor structure somewhere, and if so, what and where?

Sorry for all the questions, everything has taken much longer than expected, and I want to get the floor heating down this week, so I can finish the walls, and start tiling. I ripped out this bath a little over a year ago, and I think it is high time I finally got it finished.



07-14-2004, 05:26 PM
I'm not an engineer but i think you've got too many things going on ther for just 1/4 cbu to take care of. Looks to me like you need some plywood to add integrity then your cbu.I can't see the alcove,or don't understand what you're saying,and i'm probably not the only one, but if i'm wrong ,SOMEBODY step up.

07-19-2004, 08:53 PM
Dave, the alcove is at the top of the pictures at the beginning of this thread. The problem is that the joists run the opposite direction. Oh, and the fact that the ceiling is 6' high at the center, or at least it was with the previous floor. The last picture shows the detail at the threshold between the main area and the alcove. The alcove sort of sticks off the front of the house, so the doubled up joist at the bottom of the last picture is the rim joist. The gaps between the blocking were filled in with mud before running the tubing to provide a level base for the aluminum extrustions.

New thread (sorry for starting new one):