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Cracks in subfloor


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02-09-10, 01:36 PM   #1  
Cracks in subfloor

We pulled up the tile on our bathroom floor to find 1/2 to 3/4 of an inch of mortar on top of the plywood that was underneath it. There are alot of cracks in the mortar. And some of the mortar around the tub actually came up when we pulled up the tiles. We are going to replace it with 12" square by 3/8" slate. My question is: is there something I can put on the floor like leveler that will seep into the cracks and strengthen the floor or do I have to pull all the mortar up and reinforce with 3/4" plywood and backerboard.Thanx Jim


Last edited by jmnew51; 02-09-10 at 04:12 PM.
 
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02-09-10, 02:47 PM   #2  
Hydraulic cement might work.

 
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02-09-10, 04:11 PM   #3  
Thanx for the reply pulpo. I thought about that or just using some floor leveler. Something that will seep down into the cracks.Jim

 
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02-09-10, 04:54 PM   #4  
I've never used a floor leveler, so someone else will have to comment on that.

 
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02-09-10, 05:55 PM   #5  
You've got to use backerboard or Ditra anyway. If you use backer, you can't use the leveler, as your screws will crack it and render it useless. I have never used Ditra, so let some of the guys who have answer about that and leveler.

 
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02-10-10, 06:17 AM   #6  
If what you have there is only 1/2" to 3/4" it has to come up. A mud bed needs to be minimum of 1 1/4" over a plywood subfloor. Your best bet would be to replace it with another layer of plywood and an isolation membrane like Schluter Ditra. Depending on the height that you want to get to, you could use the appropriate thickness plywood. Don't use any plywood less than 3/8" thick.

 
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02-10-10, 08:11 AM   #7  
Thanx for all the replies.Should I use backerboard over the plywood?Thanx Jim

 
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02-10-10, 10:09 AM   #8  
You can either use cement board or an isolation membrane over the plywood.

 
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02-10-10, 02:25 PM   #9  
Thanx everyone for all your input. I already started chunking up the floor. Boy, what a slow proccess it is.Jim

 
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02-10-10, 04:16 PM   #10  
One more question guys. Can I put a coat of leveler over the backerboard.ThanxJim

 
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02-11-10, 06:05 AM   #11  
You can if you need to. Do you know for sure the floor is not on plane?

 
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02-11-10, 06:57 AM   #12  
Yes I put a straight edge on the floor.Thanx Jim

 
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02-11-10, 03:24 PM   #13  
Well I put leveler on the floor and I still have about a 1/16 of an inch of deflection on 4 ft. Is this a big deal? I'm laying 12"x12" slate.ThanxJim

 
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