ceramic tile over OSB

Joe

If you are referring to the header over the window, it's 2x10's boxed with 2x6's top and bottom. The opening was originally designed for a wider window and was later changed to a smaller window and moved to one side.

The 1/2" osb was originally laid down to facilitate the building of the shed dormer walls and to get the roof on. The framing was done late in the year last year and we were concerned primarily with getting the roof on and closing it in since this is in the NW and could get hit with early snowfall. The floor was originally designed to be 2x6 T&G but it was not delivered on time so the framing sub contractor decided to use what he had on hand. The next concern was that the radient floor heating would not be efficient under a 2x6 solid wood floor and so it was decided to add 3/4" T&G pine flooring to the existing 1/2" osb. That has not been done yet.

It should also bo noted that the 2nd level floor is only open span in the front area of the house. Originally that area was not going to get a 2nd floor. We added it to reclaim the space. In the rest of the house, the 2nd floor has many supporting walls under it. See the picture below looking toward the rear two thirds of the house. Therefore, in the area where the tile will be added, the engineered floor joists are supported from underneath by walls.

Just for further information, the exterior framing is 2x6. That is covered with 1/2" OSB and the siding is solid log 2" x 9" screwed to the outside walls. The roof is supported through to the basement floor (9" concrete) with those 2 huge logs that run the full length. They are keyed into horizontal log beams under the ridgeline with a gluelam on top of it that support the engineered roof beams.

I had this article in my files...it is courtesy of John Bridge.

• Ceramic Tile Floors

- John P. Bridge ( May, 2005 )
“Ceramic tile floors. Sounds simple, doesn’t it? Pull up the rug and “put down” tiles. Smear grout in the joints, clean it up and move back in. If you have vinyl on the floor you can go right over it with the new tiles, as vinyl makes a wonderful uncoupling membrane. Tile mastic works better for tile floors than thin set mortar does, especially when using large tiles. If the floor structure seems a little spongy, you can correct it by nailing down cement backer board before installing the tiles themselves.”

You have just been presented with a paragraph-size synopsis of the type of tile misinformation you might receive on the Internet, in tile and flooring outlets, at big box stores and in certain printed publications, not to mention home improvement shows on radio and TV. Yes, there are thousands of “experts” out there poised and eager to set you straight and get you on your way to tile flooring bliss. Don’t buy into it for a minute.
In the next few paragraphs I intend to give you a very brief overview of the correct ways that ceramic tile flooring should be installed. I’ll list sources of further reading at the end.

First of all, ceramic tiles (to include porcelain tiles, quarry tiles, various paver tiles and others) are hard, brittle and breakable. For them to be installed successfully on floors they must be well bonded and well supported underneath. If your floor is the least bit springy or “mushy” when you walk on it, it will be necessary to do some serious shoring up before tile setting begins. I cannot over-emphasize this. For our purposes, the tiles themselves have no structural value of their own. The use of cement backer boards or various membranes will not ameliorate an unsound floor structure.
• Cement Backer Boards
Cement backer boards, such as PermaBase, Wonder Board, Durock, Hardi-backer, and others are used to “uncouple” a tile installation from the subfloor below. Before they are fastened, CBUs, as they are called, are bedded in thin set mortar, which is the usual adhesive used in setting floor tiles. The panels are then nailed or screwed to the subfloor following manufacturers’ specific directions. CBUs do NOT improve the stiffness or structural value of the floor.
• Anti-fracture Membranes
There are various membranes on the market that accomplish the same uncoupling effect that CBUs provide. Two of the biggest names are Nobleseal and Ditra. I happen to be in cahoots with Schluter Systems, makers of Ditra, and I consider it among the best products on the market. But membranes will NOT rectify an insufficient floor structure. Vinyl linoleum and tar paper certainly won’t do it either.

• Adhesives
“Thin set mortar” is a portland cement product that is used to adhere ceramic and stone tiles to a “substrate.” The substrate is the layer directly under the tiles, i.e., cement backer board, Ditra membrane, etc. Thin set comes in a powder form that must be mixed with water just prior to use. Thin set cannot be pre-mixed before it is needed. It will “set-up” and become hard just like any other cement product. It does not need air to do this, and you can’t keep thin set in a can or plastic tub on a store shelf.
Therefore, any product you see on the shelf purported to be “pre-mixed thin set” is not thin set and cannot be used to install floor tiles. It is instead some sort of mastic, which is an organic glue that might be used to install certain very small tiles on a kitchen back splash, for instance. The same goes for “pre-mixed grout.” Real tile grout is made from portland cement also, and in my opinion, pre-mixed grout should not be used for anything at all.
Remember that thin sets and grouts will ALWAYS come dry in a sack or box, and remember that it is impossible to pre-mix them and keep them from setting up hard as a rock.
Tile mastic, the organic glue, can be used only on small tiles and in areas that don’t get wet. It should not be used on stone tiles at all as it can be absorbed into the stone where it can cause stains. And tile mastic should not be used for ceramic tile floors.

It is actually a 12ft 9" span wall edge to wall edge, and the joists are actually 1.5" x 9.25" and the species is fir in reasonable condition with no grade marks but very old and very hard, and the 3/4" OSB is floor grade and it is glued with sublfloor adhesive, and nailed with 6d ring shanks from a hitachi nail gun with 80lbs of pressure by a hulking great guy that stands 6' 6" and weighs 280lb in his bare stocking feet, and that's before breakfast!

The issue is the floor thickness. The radient heat is 1/2" pex with 2 runs per joist bay under the subfloor with aluminum conductor plates. The thicker the floor gets, the less heat will get transferred through it, or that is what I am told. Thats why we were told not to use 2x6 finished plank flooring and we opted instead for the 3/4" t&g. We don't want wood flooring in the kitchen and bathrooms so we decided to go with ceramic tile, but we have no experience with laying ceramic tile.

This project is very rural. There are no inspections, and very little code although we have tried our best to adhere to code or better. We are told that we have actually built it stronger than it needed to be. We do want to do it right, it is afterall our house, not someone else's We hired a contractor to oversee the project but not to build it. We wanted to build it ourselves and we have done 90% of the work ourselves. Now we are coming down to the finishing, the devil is in the details as they say. The photo's I have supplied are fairly old right now, the house logging has been compleated and I chinked the entire house myself this summer which although it wasn't necessary, has added a lot of charachter. It is a very striking house, built on 5 acres of Montana Prairie, quite different to anything around here and it gets a lot of compliments from the locals.

From what I see on this forum, you are the expert when it comes to ceramic floor tile. We very much appreciate any advice you care to give even if the advice is to not put down the ceramic tile.

snowchild said:

Terrific! And that means what exactly? I know it means the deflection allowed in the floor but the question is how do we physically measure if there is deflection in the floor?

Click to expand...

You don't have to measure it, we have charts that tell us the deflection if we have all the correct info. However, they make deflection dials or you could build a jig that would measure how much a joists sagged when loaded with a certain amount of weight.

The max deflection allowed in the industry for tilework is L360. (1/360). That means one inch sag in 360" of length or any part there of. That is also the min. code for non-sleeping rooms, which means it's the worst in can be to pass. Building to code is not something anyone should be proud of. Kinda like striving to get thru school with a D- average. You should build better than code.

Now that you remeasured the span at 12' 9", you're good. Yes, 2x10's measure 1.5x9.25. Using 3/4" subfloor and going ceramic for the kitchen and bath is the right thing to do.

As for the heat, follow the manufacturer's directions and you'll be fine. I like Ditra for floors like this. I like the uncoupling aspect of Ditra, helps reduce and hopefully eliminate shrinkage and expansion cracks.

Jaz