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Is cement board absolutely necessary?


BaumHaus's Avatar
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06-18-15, 01:21 AM   #1  
Is cement board absolutely necessary?

Quick question. I have sub floor of 3/4 planks. Screwed those to the floor joists with 2 1/2 deck screws. Put 1/2 plywood on top with 1 5/8 deck screws (not into floor joists). Is it that important to put a layer of 1/2 concrete board next. Don't want to cut corners so just making sure. Maybe I could get away with 1/4 cement board instead?

 
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06-18-15, 03:06 AM   #2  
Depends on whether or not you are installing tile. If you are installing tile, it is absolutely necessary that you install 1/4" cbu on a bed of thinset, screwed to the subflooring. (1/2" is for walls) What is more important is the structure beneath. You can post the size of floor joists, their spacing and the unsupported span, and we can better assess that part as well.

 
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06-18-15, 04:35 AM   #3  
The cement board is not a structural component of the floor, it is there to provide a bonding surface between the thinset mortar and tile. Thinset does not stick well to plywood thus the need for an optimal surface to bond everything. You set it in a bed of mortar to eliminate any vertical movement from voids to provide for a solid surface.

Don't want to cut corners so just making sure.
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06-18-15, 05:32 AM   #4  
If you are putting down carpet, vinyl or some kind of laminate then no cement board is not needed. If doing tile then yes you need cement board. In my home I did a mixture of 1/2" cement board and 1/4" Hardie backer as an experiment (it also allowed me to get the floor elevations to closely match for easy transitions). 11+ years later there has been no cracking in any of the floors so in my case 1/4" was entirely sufficient.

 
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06-18-15, 04:56 PM   #5  
sorry i left out some details. Yes i am putting in ceramic tile. You have answered that question. The floor joist are 2x8 with 16 inch centers. Appreciated the response. going with the 1/4 inch wonderboard. Will probably also tape and seal the joints. Is this overkill?

 
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06-19-15, 08:44 AM   #6  
No, taping the joints is standard.

You've still left one question unanswered - what's the span of the floor joists?

 
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06-21-15, 08:40 PM   #7  
Thank you. The span is approx. 12 feet

 
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