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02-01-2014, 12:00 PM
Hi, I had been smelling mold for a while in our upstairs bathroom. So I removed the toilet and found mold. I then removed the vinyl flooring and also found mold. I continued the remove flooring until I no longer found mold. (There was also mold by the bathtub flooring) The bathroom is currently gutted now (all the way down to the 1/2 inch subfloor. My plan is to put 12 by 12 tile on the floor, replace the bathtub, toilet and vanity. My "Deflecto" value is L/766 (ok for ceramic or stone tile) i My question is a 1/2 inch plywood subfloor strong enough for a arcylic bathtub with a mud bed? Also with wanting to tile (1/4 inch thick) how much subfloor and underlayment will I need? Do I need to remove the current undamaged 1/2 inch subflooring and start over or???
My plan was to keep the existing subflooring and put a 5/8 plywood with Ditra over the top then tile. Will this work?

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Dave Taylor
02-01-2014, 01:02 PM
1/2" ply on it's own is not strong enough for ceramic, and stone needs two layers of grade "C" or better exterior glued plywood. Usually the thicker plywood is placed below the thinner..... what's under your 1/2" ply now?

And.... may we ask just what kind of substructure this floor has.... joist condition and type, joist width, height, DOC and unsupported length?

02-01-2014, 01:45 PM
Under the 1/2 ply is a 2X10 joist 16oc looks like douglas fir in good condition
It is hard to measure the unsupported length but 12 ft is guess

Thank you for the welcome

Bodie Powers
02-01-2014, 02:43 PM
My "Deflecto" value is L/766

and later in the thread....

Under the 1/2 ply is a 2X10 joist 16oc looks like douglas fir in good condition
It is hard to measure the unsupported length but 12 ft is guess

These statements seem to be at odds with each other. You'll need to measure the span to determine whether your joists are suited for ceramic or stone tile. Do you have access to where you can use a tape measure?

02-01-2014, 02:54 PM
Ag, bear in mind that the "span" that's being requested is not the distance the joists run within the room. It's the distance they run from one support to the other. There could be a beam that supports them at the end or anywhere underneath, a wall underneath, or they could possibly run from the foundation wall to foundation wall. Whatever that span is, that's what you plug into the Deflecto.

It would be very unusual for your joists to be at the deflection rating you posted unless it was spec'd that way at construction.

Also, do you plan to use ceramic tile or stone for your new floor?

My two cents worth on your existing subfloor: I would remove the subfloor and replace it with 3/4" tongue and groove plywood, glued and screwed to the joists. If possible, I'd also run it under the tub. Then you could install an appropriate tile underlayment and tile. An even better plan would be to add a layer of 1/2" ply over the 3/4" ply.

This plan is, of course, assuming that the joists are adequate to support a tile installation.

02-01-2014, 02:59 PM

I ran your numbers through Deflecto and can up with L/558, still good for ceramic but much lower than the numbers you posted.

Thank you for using the John Bridge Forums Deflect-O-Lator :-)
For joists that are SYP or Douglas Fir, in good condition, 9.25 inches tall, 1.5 inches wide, 16 inches on center, and 12 feet long between supports, the deflection calculated is 0.258 inches.
This translates to a deflection of L / 558.

It's really important to get a accurate span length for these calculations, is there a way to measure from below?

Edit: too slow on the S3! Kevin's way ahead of me.

02-01-2014, 03:28 PM
The "span" is from the where the joist is supported on the outside wall and a stell beam in the basement The joist is mostly hidden by the finished basement.
Perhaps I am not as skilled with the deflecto tool as others. So are you saying to replace the 1/2 flooring with 3/4 T&G. Is that alone enough to support the travertine tile? Or should I add more flooring to get to 1 1/4 inch and if I do that how will it effect my toilet flange Too low with the tiling? Your thoughts?

02-01-2014, 04:20 PM
In order to install travertine, which is a very soft stone, you're going to have to do some work on the joists. They will either have to be sistered, i.e. have a 2x of adequate size mated to them with glue and screws, or add some type of support from underneath to cut the span.

Then, you would definitely need to remove the 1/2" ply, install 3/4" ply and 1/2" ply on top. Then you would need a tile underlayment and your travertine would go on top.

If your dead-set on having travertine, that's what you have ahead of you. If you're willing to find a porcelain tile that looks something like what you want, you'll have a bit less work to do.

There are ways to compensate for the toilet flange sitting low. Don't worry about that part. :)

02-01-2014, 04:21 PM
Just to clarify, the entire bathroom falls within this area between this exterior wall and the beam, correct?

If so, can you find out the distance between the wall and beam?

02-01-2014, 05:22 PM
Thanks Kman just looke up the tile... it is ceramic
12 ft from outside wall to beam

02-01-2014, 06:46 PM
2x10's on 16" centers spanning 12' is good enough for ceramic tile, but not stone.

02-02-2014, 06:01 PM
Ok, so if I remove the 1/2 inch original subfloor and lay down a 3/4 piece of plywood will I need another piece of plywood 1/2 inch with the Ditra or should I use CBU under the Ditra?
Also is 23/32 exposure 1 good enough? Not many places sell 3/4 T & G

02-02-2014, 07:21 PM
CBU and Ditra would be redundant. Use one or the other.

The layer of 1/2" ply on top is more like added insurance. It's not a requirement, but it adds greatly to the strength of the floor.

For the 3/4 ply, I like to use Sturdi-floor. It's available at Lowe's in my area. Look for something with a face grade of "C" or better. Anything with a "D" grade stamp or that has the word "sheathing" on it is not recommended.

02-03-2014, 11:50 AM
Only place I've seen Ditra over CBU is on Holmes on Homes. Both are certainly not needed and I only think he did it to make up height.