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Several Pieces of Subfloor Replaces, What do I need to do before tile?

Several Pieces of Subfloor Replaces, What do I need to do before tile?

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Old 10-16-17, 08:14 PM
M
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Several Pieces of Subfloor Replaced, What do I need to do before tile?

Hey guys. I did a search and didn't find specifically what I am looking for so hoping I could get a bit of help. I plan to lay large format 8"x40" porcelain tile (https://www.msistone.com/wood-look-t...eleste/nutmeg/) over 600 sqft of subfloor. In having some electrical re-done I had to take up two pieces of subfloor that were tongue and groove 3/4". The joists are 2"x12" spaced 24" apart. I was unable to find new tongue and groove subfloor and would have had to cut one of the tongues to install anyway so I laid new non-T&G 3/4 plywood.

I am now noticing that if I put all my weight on the new subfloor in the middle of a joist and right at the edge I am able to get the wood to flex very slightly (probably 1/16"). My original plan was to lay 1/4" cement board and then tile over that. Now I am wondering if I need to do something to stiffen up the subfloor so that I don't run into problems.

I have posted a picture of the subfloor, and when I place all of my weight on the subfloor to show the flex (a bit over 200lbs ). It is somewhat tough to tell in the picture but I can feel the flex a bit when I rock my weight over the seam. The question is should I a) go with original plan of 1/4" cement board and then tile b) lay another layer of some kind of subfloor, provide recommendation please or c) go with a product like Ditra XL which is stated to be laid right on 3/4" subfloor and tile on that although I don't have experience with the product I have heard it is good.

I am not really sure how much if any flex is acceptable so I really appreciate your help.

Matt
 
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Last edited by mnispel; 10-16-17 at 09:44 PM.
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Old 10-16-17, 11:00 PM
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Hi Matt,

You might have been ok by just installing supporting lumber from below (blocking) instead of installing another layer of underlayment, but I think the 24" oc is a problem. I mean...I know Ditra XL will usually work well even when the joists are 24"oc, but there's certain ways the sheets need to be installed, using good glue and fasteners AND the panels need to be spaced, which yours do not appear to be. Then of course no t&g in some places. Also looks like you grabbed the cheap grade of ply. Is that exterior glue rated Exposure 1?

Therefore I suggest adding min. a full 3/8" underlayment grade ply or better yet 1/2". I might also block the seams too.

Don't forget about expansion joints in the tilework regardless of which way you go.

BTW, when measuring deflection a 300lb mass is used. Did anyone run the framing #'s to see where you are for deflection?

Jaz
 
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Old 10-19-17, 11:32 AM
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Thanks Jaz. I have blocked off the seam and will lay an additional layer. Appreciate the help!
 
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