Concrete between the joists? [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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03-04-2007, 12:03 AM
I am looking to re-tile a small bathroom floor (30 sq ft), house was built in 1920.

From the basement, I can see that the space between the joists has been enclosed using what looks like old floor boards. They then filled the joists with concrete, followed by metal lathe and what appears to be deck mud and then tile. Then there is a second layer of tile, added by the previous owners which looks like they did while heavily intoxicated.... its terrible.

Should I just rip all this out and put down a new subfloor?

Was this a common practice (to fill the joists with concrete)?


- Jason

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03-04-2007, 12:12 AM
You are looking at a mudbed, a good way to set tile. If you can preserve it, you can tile over it. But, if it gets broken, you'll need to remove it. You could do another one. Note, a mudbed is much more forgiving than the joists with a subfloor. You would need a new subfloor and MIGHT need to reinforce the joists if you don't do another mudbed. It is easier to make a mudbed on top of a subfloor, but you'll end up with a thicker floor than the technique they used. Use the deflection calculator "deflecto" in the blue bar above.

Rob Z
03-04-2007, 12:14 AM
Hi Jason

That was a common method up through the early sixties. You'll likely find that the tops of your joists are hatcheted to a point, and that they have been butchered in places by the plumber from long ago.

You could demo the upper layer of mud and leave the stuff in between the joists, and then float a relatively thin bed on top of the stuff down in the joists. This might be a bit tricky, depending on what's there.

We usually demo all of it out and strengthen the joists as needed, then follow with plywood subfloor and a mudbed over paper and metal lath.

If you can get it flat enough by scabbing onto the existing joists, then plywood followed by cement board or a membrane such as Ditra or Noble TS would be a bit easier than a mudbed.

Rob Z
03-04-2007, 12:17 AM

Before considering whether to tile over the existing, check to see if there are any cracks, particularly ones that correspond to the locations of the joists (most common over the hatcheted joists I mentioned above).

03-04-2007, 12:29 AM
Thanks for the quick replies (at 1am no less!).

I don't think there is any way to save the existing mud bed. I did some exploratory surgery earlier today, and there seem to be some cracks.

Whats the best way to remove it? Rotary hammer?

03-04-2007, 12:59 AM
Whats the best way to remove it? Rotary hammer?

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03-07-2007, 09:55 PM
OK, i decided to rip off all the tile and see what was there.

The cracks I saw before were contained to the small area I started in (go figure) and they were just small surface cracks.

SO now I have a floor with just a few gouges (1/4in deep at most) from removing the old tile. Can I just fill them with thinset and set the tile? I am laying 12x12 marble, and plan to use Custom's "Marble and Granite" modified medium bed thinset.

Does this sound like a viable plan? Anything else I should consider?