Need advise on floor tile project.

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Old 03-27-06, 11:03 AM
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Question Need advise on floor tile project.

Project details:
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24' x 24' family room, with a full bath and utility room that are connected
2 x 8 floor joists on 16" centers. Span is about 7.5 feet
sub floor is 3/4" T&G OSB, nailed every 24", Liquid Nails and 2" screws every 6"
12" x 12" ceramic floor grade tiles
Home is in North Eastern North Carolina
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Questions: debating what to use for an underlayment. I know I need to use 1/2" cement backer of some type in the bath and utility room. My dilemma is I have a full hack of really nice and flat finished 3/4" plywood I could use in the family room screwed down every 8 inches to make a very strong and solid floor. I know this would be stronger than Durock, Hardibacker and DensShield BUT I would not have the moisture protection. Would I need to use mastic or thinset if I were to go that way. Also another problem is I would have to build up the bath and utility another 1/4" to match the plywood part. Should I give up on the slightly better strength of the plywood and go for the stability and moisture resistant backer and if so ..what would you recommend? I can't decide. Durock is messy but this is a easy job. Not many cuts. I have used Hardibacker and it worked fine but it's only 2 years old where I used it. I had problems with grout color consistency where the color on the seams of the hardibacker was darker when then grout dried. Never used DensSheild before but have a friend that won't shut up about how easy it was to use. I don't need moisture proof in a family room so much as I want more strength and I don't think that DensSheild is all that strong ..after all it's drywall basically right? Going nuts here ..ready to get started. If you guys have time ..shoot me your thoughts. Thanks in advance!!

Paul Mathews
North Carolina
 
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Old 03-27-06, 01:04 PM
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NONE of the tilebacker boards will offer you more strength, only the plywood would do that. But plywood isn't that easy to tile over so you should use a tilebacker also.

If it were my job the way you desribe it I would use the plywood first, then for a tilebacker I would use Noble CIS. Noble CIS will offer a thin layer of isolation from the plywood and structural movement. It will also offer a moisture barrier which is neither here nor there in this case but it would be better to have it. CIS would also be the thinnest underlayment application you could have so that transitions aren't a major issue for you.

Mastic is out, thinset is what you should use.

The joist is is somewhat problematic and this is why you need the plywood assuming your span is only what you claim.

Denshield is easier to work with but I wouldn't go near the stuff for any reason.

Schluter DITRA is also a great tilebacker but it is thicker than the CIS.
 
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Old 03-27-06, 06:33 PM
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thanks for the info!!! so you don't think 3/4 plus a 1/2 inch hardiboard is enough strength? this floor already is like walking on concrete. It's solid already. I see your point with the plywood and the moisture backer. I might run into issues with door clearance
 
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Old 03-28-06, 09:23 AM
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OK now I'm confused, which isn't unusual for me.

Using 1/2" CBU over 3/4" OSB is done all the time, but I usually don't recommend that someone install tile directly to plywood. (The OSB must be t&g and not square-edge) This (tile on plywood) can also be done but it requires some particular thinset products to gaurantee a lasting job.

The minimum requirement for subfloor thickness BEFORE the tile is 1-1/8" to 1-1/4", more is better. So your proposal meets that minimum, but it is only a minimum.

The CIS and/or DITRA (over the additional ply) would add minimal thickness and at the same time offer a compatible "tooth" for the thinset to adhere to. Neither would offer any additional structural value.
 
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Old 03-28-06, 12:13 PM
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Originally Posted by Bud Cline
OK now I'm confused, which isn't unusual for me.

Using 1/2" CBU over 3/4" OSB is done all the time, but I usually don't recommend that someone install tile directly to plywood. (The OSB must be t&g and not square-edge) This (tile on plywood) can also be done but it requires some particular thinset products to gaurantee a lasting job.

The minimum requirement for subfloor thickness BEFORE the tile is 1-1/8" to 1-1/4", more is better. So your proposal meets that minimum, but it is only a minimum.

The CIS and/or DITRA (over the additional ply) would add minimal thickness and at the same time offer a compatible "tooth" for the thinset to adhere to. Neither would offer any additional structural value.
Thanks again Bud . What I have now is a clearance problem if I were to do both the 3/4 plywood AND anything else. My 3 main steel entry doors in this space will be close to 3/8" after thinset, 1/2" backer and then the tile. I was thinking I could could do plywood OR 1/2 backer but not both because of that clearance issue. I don't want to put tile on plywood ..but would love the strength. Like I said I have a solid 3/4 T&G subfloor on #1 sothern yellow pine which spans farther than fur. It's spanning less than 8 feet on 16's. screwed down and nailed and glued. It's strong. I was just hoping to use this entire hack of 3/4 I have and I have given up on that idea now It's gonna have to be the sub of 3/4 plus the thinset and 1/2 backer ..which is 1.25 plus if you count the thinset I guess in between. Fingers crossed. Wife says is it cracks later bust it out and do hardwood and leave tile in the bath. Oh well ..we will see. Thanks for all the input!!!
 
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Old 03-28-06, 12:41 PM
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Seems that there is always a sacrifice and a trade-off in the tile installation business. Compromise is common.
 
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Old 03-28-06, 12:55 PM
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1/2" ply and a membrane as Bud suggested is the way to go here. Not much difference in height than the 1/2" cbu. Even 3/8" ply and a membrane would be a better alternative to the 1/2" cbu.
 
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