Decoupling membranes and thickness

shazapple · 01-11-2012, 09:27 AM

What options are there for a decoupling membrane? I am going to put down ceramic in my kitchen. I've checked the spans (2x7.5" 10 feet and 24" oc) and they are good. The floor is two layers of 3/4" T&G boards which I will
A) remove one layer of T&G, add 3/4" exterior grade plywood screwed every 4", modified thinset with 1/4" trowel, 1/2" backer board (or Ditra XL), unmodified thinset with 1/4" trowel, and tile or
B) Leave existing floor, add 3/8" exterior plywood screwed, decoupling membrane (ditra or other?), tile.

The aim is to match the height of the 3/4" hardwood in the adjoining room (which is on top of the 2 layers of T&G board). What else can I use for a decoupling membrane that would bring my height down? Do I have any other options to consider? Thanks!

JazMan · 01-11-2012, 10:06 PM

Hi,

Quote:

I've checked the spans (2x7.5" 10 feet and 24" oc) and they are good.

Please tell me which species and grade of 2x8" joists spaced 24" apart yields a deflection rating higher than L360 at any load factor other than the basic 40/10 live/dead load. I'll await your answer.

Jaz

shazapple · 01-12-2012, 08:50 AM

Either Pine or Douglas Fir. It is an older house, so it is rough sawn and true 2" by 7.5". The span is also closer to 9 feet but I went to 10 for a bit of a safety factor.

JazMan · 01-12-2012, 05:34 PM

That info would have been helpful if it had been included in your original post.

How come two layers of 3/4" boards? Is the top layer hardwood flooring? If so, that is different than two layers of 3/4" boards, (planks). Is the first diagonal over the joists?

You'll want the top layer to be plywood, not planks. Depending on what the top layer is will determine my answer as to which way to finish. Get back.

Jaz

shazapple · 01-13-2012, 01:09 PM

Thanks in advance for the help, I know you and Bud are the guru's around here! The house is over 100 years old and originally started out as a cottage, so a softwood T&G floor was probably the easiest floor to put down. Here's the original construction, which still remains:
2"x7.5" rough sawn joists 10ft long, 24" oc
3/4x4 T&G pine plank subfloor perpendicular to the joists
3/4x4 T&G pine plank finished floor parallel with the joists

The living room floor (which butts against the kitchen floor, covered by a metal transition strip) has 3/4" T&G oak hardwood floor parallel with the joists (in addition to the original construction). The kitchen currently has 1/4" plywood, vinyl, 1/4" plywood, and another layer of vinyl (in addition to the original construction) and butts up against the living room with a metal transition strip. The oak is the floor height I am trying to match, as it will be staying.

If I remove everything in the kitchen except the T&G subfloor I'll go with 3/4" plywood, ditraXL (or 1/4" CBU), and tile (very close to oak floor height)
If I leave both layers of T&G boards, I'll go with 1/2" plywood, decoupling membrane, and tile. What are my options for a thin decoupling membrane? (remember I am trying to match the oak floor height, and assuming 3/8 tile I'm already a bit above)

Thanks again for the help!

JazMan · 01-13-2012, 09:57 PM

Quote:

If I remove everything in the kitchen except the T&G subfloor I'll go with 3/4" plywood, ditraXL (or 1/4" CBU), and tile (very close to oak floor height)

Ditra XL + tiles should give you the best height match. Ditra XL was developed for just this application. (to match up to 3/4" hardwood).

If you go the other way, (1/2" ply, Ditra, tile), you'll be about 1/4" or so higher than the hardwood side.

Jaz

shazapple · 01-14-2012, 10:29 PM

Thanks Jaz for your help. I'll be ripping up the floor this coming week.