Cracked cement subfloor... what to do?

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Old 09-14-04, 07:14 PM
u2slow
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Cracked cement subfloor... what to do?

I just chiseled off most of my bathroom floor tile. The tile was set on a 1-1/2" solid cement subfloor. Some of the cement came up with the tile, especially around the perimeter. Some places right down to the shiplap. There's a few long cracks running through it, and on one spot is creaks when I shift my weight from leg to leg.

I want to install 12" ceramic floor tile. Will patching the subfloor be a lasting solution? If I tear it out, do I replace it with new cement, or ?????
 
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Old 09-15-04, 09:15 PM
A
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That's a tough call. If the cement was just damaged on the surface it wouldn't be too bad, but since it is moving when you walk on it, it's not a good surface for ceramic tile anymore. Getting down to the shiplap at this point, may be the best solution. Once you get the cement out and clean it up...you should screw down the shiplap with deck screws to tighten up the floor and stop any movement/squeeking. Then a layer of 5/8th plywood, screwed down over it. On top of that install cement board. THe cement board should have a layer of thin set under it, but this time try not to put the screws into the floor joists if you can. This will help isolate the cement board from the stresses in the floor. By then you should be ready to start tiling.
 
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Old 09-16-04, 07:42 AM
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I think that you may need to put down something on top of the 5/8 plywood. If you need to make up 1.5 "---- 5/8 ply + 1/2 cb is not going to do it. You may want to find some configuration of plywood and cement board and adhesive that will end up with the tile fitting under the toilet flange. It can be higher than the flange but not lower. Just a thought
 
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Old 09-25-04, 03:24 PM
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Installing tile on cracked concrete

Cracks should be repaired. An anti-fracture membrane should be installed over concrete. This special membrane is installed on top of thinset. It will prevent cracked tiles due to crack movement in concrete. Then, you can install tile with thinset on top of membrane.
 
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Old 09-26-04, 03:21 PM
floorman
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What this is a sand /cemnt mix called a mud bed,if this is cracked and/or moving this needs to come out and redone or like jone says if you need to bring this up the original heighth then figure out a way with the plywood and the c.b.u to do this.Do not attempt to put a membrane over this and tile cause it will fail.The reason i say this is because the mud bed is just laying there and any kind of membrane will not stop the movement of this mud and it will transfer through to the tile and the tile will crack as well
 
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Old 09-27-04, 03:52 PM
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I agree. What you're working with is an old style mortar bed someone built for the floor. Once it's damaged and/or cracked it needs to either be rebuilt, or a suitable replacement needs to be considered. You'll need to break it out, and plan on building a new floor.

In my 1926 Craftsman home I had something similar in my bathroom when I gutted it for a remodel. Someone actually went to the trouble to trowel the mortar bed concave so the water would move to the center of the room. Very cool.

But by the time I got to it it had been a victim of previous remodels. What I got to start with was an attempt at patching the broken mortar bed from the previous remodel. They also expanded the bathroom a few inches into the adjacent bedroom, which left a gap between the mortar bed and apron tub. They tried to "marry" a piece of 1/2 wonderboard with some adhesive to the front of the mortar bed to make up the difference, but didn't seal the joint between the front of the tub and the wonderboard with a membrane, and did a lousy job patching the mortar bed.

A couple years of movement weakened the patch job, and ultimately defeated the whole purpose of the mortar bed alltogether. No membrane meant moisture was free to run in between the tub and the wonderboard, saturate it, and make its way into the shiplap. The result was a spongy floor that let moisture get into the shiplap from the apron tub, and ultimately the floor joists.

All of the shiplap (3/4" cedar) had to be torn out. The floor joists (2" x 8") had to be doubled up with new beams to add strength to the weakened members to prevent floor deflection (the plumber from the previous remodel had replaced the iron pipe with copper, but managed to split three floor joists by notching the beams on the bottom). I used 3/4" tongue-and-groove floor grade plywood and ring shank nailed it to the doubled-up floor joists using heavy duty construction adhesive. Then 1/2" wonderboard was laid down with unmodified thinset and a 1/4" x 1/4" square notch trowel, and the wonderboard was screwed every 6-8" and 2" from the edges leaving 1/8" space between the pieces.

After using modified thinset and fiber tape made for tile backer to mud and tape the joints I had a solid, flat and strong floor that had double the floor joist strength and measured 1 1/4" thick. It was just fine for tile.

Don't cut corners on this floor, unless you want to either waste money or end up doing more damage than you already have. Tear it out, and build up a good strong subfloor. If that shiplap is damaged in any way you'll need to replace it. Most CBU manufacturers recomend that anyway, so prepare to set a new subfloor if necessary unless you want to try your hand at mudding a new mortar bed for the room....
 
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Old 10-01-04, 09:38 AM
u2slow
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I've had the chance to read posts, just not enough time to generate a response!

I ripped out the cracked mud bed... and its a good thing I did! As I got closer to the toilet, with each piece of cement I broke up, the smell grew stronger.

Once I was down to the last 30" square of mud under the toilet in the alcove, that whole thing was lifting up with my prybar. I tried to unbolt the toilet - the bolts broke as they had almost rusted away. So the iron flange came out *with* the toilet - revealing a 4" lead pipe with a kink in it. Seems as though the plumbing and house settled differently, so the 3/4" shiplap floor was digging into the side of the pipe making it D-shaped and making it too short to seal on the one side.

Fixed it with a sawzall and a hammer

I decided to put in a new mud bed. Re-screwed the floor, tar-paper, 2.5lb diamond mesh, 3:1 cement/sand mix, Blue Seal membrane, and finally the tile.

Here's a pic on the finished mud bed

I have new respect for tilesetters! My Dad did the mudbed in my basement several years ago, and a friend (a pro tilesetter) did they tile. They sure made it look easy
 
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Old 10-01-04, 09:51 AM
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Lookin good! Yeah you would have gambled and lost if you decided to keep that floor as-is. Sounds like the moisture from the drain was saturating a section of the floor. Nothing kills that shiplap faster than moisture.

Good work. Are you just tiling the floor or are you tiling the walls too?
 
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Old 10-01-04, 12:18 PM
u2slow
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I'm putting 3" cuts of the floor tile on as a baseboard. Walls are just getting paint.

Are you wondering about my greenboard? It was leftover from the tub enclosure... I used four sheets of cement board, but had a few inches left around the top that I filled with greenboard and covered in thinset.
 
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Old 10-01-04, 02:53 PM
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Originally Posted by u2slow
I'm putting 3" cuts of the floor tile on as a baseboard. Walls are just getting paint.

Are you wondering about my greenboard? It was leftover from the tub enclosure... I used four sheets of cement board, but had a few inches left around the top that I filled with greenboard and covered in thinset.
I don't see concrete board in your pic. I just see drywall on one wall and greenboard on another, with a funky baseboard backer on the bottom of the wall...
 
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