do i have adequate underlayment/sealing for bathroom floor tile


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Old 01-18-04, 12:57 PM
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Question do i have adequate underlayment/sealing for bathroom floor tile

I am installing 12" tile in an existing 2nd floor bathroom. With additional plywood the floor is built up to 1" thick. The bathroom is apprx. 8' x 4' and the floor does not have any bounce.

Do I really need an additional backerboard?

If I do not use backerboard should I seal the seams of the underlying plywood near the bathtub or will my tile, grout/sealer, and caulking around the inteface with the tub keep the water from going below?

By the way I am asking this question after the fact for one bathroom and before I start the second one - I already did the first bathroom without additional backerboard or sealing... looks fine but now not sure if it will last.
 
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Old 01-18-04, 01:37 PM
ee3
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you will most likely be ok but without knowing joist depth and spacing just guessing.keep in mind that when the bath tub is filled (if there is one )you will be adding lots of weight that may deflect the substrate and cause problems..However after the fact I wouldnt loose sleep.
 
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Old 01-19-04, 04:06 PM
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So for the second bathroom I should use the backerboard? Or only if joists are not a certain spacing?

What is a good test if I cannot see the joists under the plywood underlayment?

How about sealing to prevent water from going down on the ceiling below?

Thanks.
 
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Old 01-19-04, 07:10 PM
ee3
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a real quick test is put a straight edge on the floor and see if adding about 300# of tile(stacked up in their boxes)in the center causes the floor to bow....measure the bow(deflection) it should not be over 1/360 of the span.(measured in either direction.If my math is correct . you can have approx.1/4" across the 8' or 1/8" in the 4' direction.....it doesnt take alot of deflection to crack tile..the number above are only guesses and also the MIN...MANY OTHER FACTORS come into play...
 
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Old 01-19-04, 08:11 PM
muley
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As a professional contractor I would not install given the parameters you've discribed. First while plywood is an acceptable substrate for tile it is hardly the optimum. Secondly 12" tile assuming your joist are 16" oc, require 1 1/8 " minumum substrate. Given the dynamics of both this points I would go with a backer unit. If install or height is a concern you could install the Schluter Ditra mat. Install is a breeze and heigth is only 1/8 inch. The mat is also water proof which is a bonus for a wet area. However, you do have to follow waterproofing directions but it is simple. Good luck.
 
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Old 01-20-04, 07:41 AM
ee3
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both tile and ditra require the substrate meet 1/360. 12 " tile has the same requirements as 8" and 16" deflection not to exceed 1/360 as tested to astm C-627
It is a MIN. - adding more is better!But may not be needed. If your talking waterproofing you could use Ditra,Nobleseal,or any number of liquids,or Trowel on membranes.
I am now wandering (after reveiw) about the statement "with additionial ply wood the floor is build up to 1" " WHAT DO YOU HAVE HERE??TWO LAYERS OF WHAT???
 
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Old 01-20-04, 02:37 PM
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Forgive my lack of knowledge of building materials but all I can see is a cross-section view when I pull up the cover for the heating vent. The bottom layer appears to be ~3/4 inch of a 5-ply board. And on top of that is what appears to be a 1/4 inch single ply board. Interestingly enough the top layer appeared to be an afterthought since the baseboard trim sits on the 3/4 inch board below and the top layer is cut to fit around the baseboard (which makes it a little tricky to remove the baseboard).
 

Last edited by geodog24; 01-20-04 at 03:29 PM.
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Old 01-23-04, 03:36 AM
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If it's 1/4" plywood, it has to go. Remove this layer, apply Ditra and tile over top of it.

The sub-floor thickness can even be 5/8" and it's still do-able. Don't be thinking you can lay tile directly over 5/8" or 3/4" plywood without Ditra.

David
 
 

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