My house is 13 years old the,last week i removed the ceramic tiles from,kitchen, hallway, washroom ,laundry rm.removed
scratch coat and mesh that the builder instaled,the tiles were
12x12 ,
,,the thickness of tile thinset mesh and scratch were about 1 inch thick,so now i have 700 sq ft of tile
to install gonna go with Ditra the tiles are 20x20inch porcelan,the joist are 2x8 every 1 ft on center,the plywood is
five eights t.g.the deflectolater says i am ok for the washroom,
hallway, and laundry rm,the kitchen is not a square area half of it is 11 ft x 7 ft joist span is 11ft which pases the deflectolater but the second half of the kitchen floor is 14ft x 10ft with a 14 ft joist span which is L /267 deflection,my question is i never had a problem in this area before with the old scratch coat and mesh will this area fail using Ditra .

Hi Sergio,

As you know, there are two components to the subfloor system. The framing or joists, and the subfloor sheets themselves.

Normally I would recommend adding another sheet of plywood over your 5/8", but since your joists are 12" o.c. I'll say you're fine. However, if you want to improve your subfloor, you can add more plywood...the more the better.

Your joists however are nothing to write home about. Most of the area is OK. Actually that area in question may also meet L360 min. standards? I would bet it does since that is necessary to as I said meet building requirements.

Please go under the floor and let us know the species, and the grade of the joists. Also re-measure the span, measure from face to face of the supports.

Jaz

,Thanks for the info,my basement ceiling is drywalled it is a
finished basement,but if i remember corectly i think the species
of wood was kiln dried spruce one and half inchesxseven and half
inches,from concrete wall to steel beam it is 14 feet,never had
a problem with the tiles in this area the floor feels pretty solid,the funny thing about all this,is in the hallway
which is 5 feet wide and joist span is 6 feet i had the grout
come out around two tiles when i was doing the demo i chiseled
the two tiles off and seen small cracks in the scratch coat i
guess thats how unpredictable scratch coat and mesh is,that is
the only problem i had in the floor .

OK, I still don't know the grade of those joists. Example; If those joists are #1 or #2, they'll meet code of L360 at up to 13' 6". If they're Structural Select, you're at L360 up to 13' 10". If you had Alaskan Spruce,you could add about 4" to the spans. These figures is when rating them at 40 lb. live and 10 lb. dead weight load. The 40/10 rule is OK for regular flooring, and is the basic minimum code for residential, but is risky with ceramic tiles. Doesn't mean it's going to fail every time, but not what we'd like.

For ceramic I recommend using a 50/20 load criteria because of the added weight, even higher would be better.

What brands of thinset do you have available to you? Where do you live? I ask because Hydroment has a product that is supossed to work even at L240. Might be something to look into?

Jaz

I am in Ontario we have Home Depot and Lowes in our area,there is no way for me to find the grade of my joists,gonna go ahead
with the install in a couple of weeks,thanks for your help and
advice.

Those two stores are only a factor if you decide to go there. You have plenty of real lumber yards and people that know lumber in Canada. Regardless, the species and grade should be stamped on every board. There must be an area in the basement that doesn't have drywall on the ceiling, try the furnace room. Or a neighbor's house built at the same time.

Ontario is a large place, I live 20 minutes from Ontario myself. I was thinking you would give me a bit more than that so I could find a place that sells Hydroment near you. But you can figure that out on your own.

Jaz

Sergio, I don't think you have calculated your spans correctly.
Ontario building code automatically specs all floor systems for a L/360 rating. It would never pass permit application otherwise.
Your lumber will be a spruce-pine-fir #2 rated product. That's the most common for our area.

If your floor had bridging and a drywall ceiling the most those joists could span is 13' @ 12" O.C.

I would think your failure has to do with the previous installtion method. Check to see if the subfloor is screwed down. If not that might be part of the problem.