new tile installation over interesting floor construction

[donq]

We are in the process of remodeling our existing home (build in the late 1950's) and I have an interesting existing floor construction situation where I want to install new porcelain (12x12 nominal) as an entry--the area will be approximately 48" wide by 10'-0" long.

the existing floor construction (main floor over finished basement) is as follows:

4x10's @ 48" oc, spanning approx. 11 feet (from outside foundation wall to 8"deep steel beamrunning down center of house); subflooring is 2x6 T&G "car-decking"; existing finish flooring is hardwood.

what makes this (more) interesting is that we have removed an existing fireplace at the exterior wall where we are creating our new entry, when we removed the stone tile hearth finish, we found a "hunk" of concrete the full width of the fireplace (approx. 48" wide <spanning from 4x10 to 4x10>, extending about 18 inches into the house) i believe the construction has some sort of "header" at the transition between the floor framing noted above.

i want to remove the existing (3/4" thick) hardwood flooring to inset the new tile so it flushes out with the hardwood flooring.
i will need to build up the concrete to match the height of the 2x6 subfloor, then install the tile over this area. since i only have about 3/4" depth to work with, what type of underlayment should i be looking to install over the existing "car-decking"

I also think my deflection will be within the L/360; the Deflectolater doesn't really address this.

i am not sure how clear and understandable this description may be, but i hope it gets us started to answer this question.

thanks
donq

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[bbcamp]

To get the deflectolator to do this floor, put in your numbers for the joists size and span, then tell it the joists are 24 inches apart. The resulting L/sumthin is divided by 2. In your case you will get L/1200 or so, so in reality, your joists are L/600 or better. Good enough for ceramic tile!

Car decking is just planks. So you must add plywood before you add underlayment. Since you want to fill 3/4", I would use 5/8" plywood, then add Ditra as your underlayment. Ditra adds 1/8".
If you have to bring up the concrete to be level with the Ditra, you can use a number of things, depending on how much you need to go. Thinset for up to 1/4", or deck mud bonded to the concrete with wet thinset for more.

You will need an expansion joint where the wood meets the concrete. This can be as simple as planning a grout line at the joint, then filling that line with a color matching caulking. If you can't accept a groutline at that joint, let us know, cause it will take a bit more headscratchin'.


Bob

[goneriding]

bb - If I read this right, I think he wants his finished tile installation to be flush with the hardwood, not his underlayment. So, he would have 3/4" for plywood, backer, AND tile... yup, pretty slim eh? I don't know the answer, but I think I get the question :)

[cx]

What Carla said. :)

Seems like he could just add 3/8ths ply (did I really say that?) and Ditra and get pretty close if his tiles aren't real thick.

The transition over that fireplace slab may be a little tricky, but I bet we could figger something out. Hell, Bob's a real Injineer, and all. :p

[John Bridge]

Hi Donq, Welcome aboard. :)

I would try to figure a way to get the subfloor to extend over the concrete fireplace footing. That way you won't have the problem of dissimilar floors meeting each other. How far below the existing sub floor is the top of the concrete footing?

[donq]

Hi Donq, Welcome aboard. :)

I would try to figure a way to get the subfloor to extend over the concrete fireplace footing. That way you won't have the problem of dissimilar floors meeting each other. How far below the existing sub floor is the top of the concrete footing?

as an update,
When we got all of the demo completed we found that the existing hardwood flooring didn't cover the entire floor area and that it would be cost prohibitive for us to try to correct this, I have decided to install the tile over the existing hardwood flooring;the concrete slab has been covered with a sheet of 3/8 inch plywood, the surface of this plywood sits about 3/4 of an inch below the level of the finish hardwood flooring (the actual difference varies due to existing conditions)

it would seem i should use some sort of self leveling fill to bring this surface up to level with the surface of the hardwood floor. (QUESTION IS: what is the best product to use for this?)

i am planning on installing the porcelain tile over a 1/2" thick hardie backer 500 board, this will allow the carpet and the finish surface of the tile to "flush-out" (ANY RECOMMENDATIONS?)

THANKS
donq

[HDtilegrunt]

THe way I read it, you have two layers of dimensional lumber, the 2x6 decking and the hardwood? It's no go over two dimensional layers, and 1/2" plywood would need to be installed over the decking (not hardwood) before installing any sort of backer, but they're not for joists over 19.2" oc either. Maybe with the ply and the 2x6 decking you could get away with it, but don't think of installing the Hardi directly to planks. 1/2" doesn't really buy you a more stable surface either as cbus are not structural. If BB signs off on the 2x's with 1/2" ply before backer, then go for that, but plan for some futher demo.

[Rd Tile]

I don't like the sound of 3/8" plywood or any wood or cbu over a concrete slab, also, I wouldn't want any hardwood flooring under any substrate for tile.:)

[donq]

THe way I read it, you have two layers of dimensional lumber, the 2x6 decking and the hardwood? It's no go over two dimensional layers, and 1/2" plywood would need to be installed over the decking (not hardwood) before installing any sort of backer, but they're not for joists over 19.2" oc either. Maybe with the ply and the 2x6 decking you could get away with it, but don't think of installing the Hardi directly to planks. 1/2" doesn't really buy you a more stable surface either as cbus are not structural. If BB signs off on the 2x's with 1/2" ply before backer, then go for that, but plan for some futher demo.

whenyou say BB signs off.......not sure i know what you mean.
my alternative seems to be to remove the 3/4" thick hardwood and replace it with 5/8" to 3/4" plywood; then install the backer board.

i will need to live with whatever deflection has occured.......since this is an existing house the only new dead load deflection will be the tile; the live load is what it is.

would there be any value in a slip sheet or cleavage membrane?

by the way, building paper was installed before the the 3/8" plywood was installed over the concrete. and this concrete is not a slab on grade or located over unconditioned space. i suppose if i am going to be ripping out the hardwood floor i can also rip out the 3/8" before i reinstall the plywood subfloor.

thanks for your advice.

[donq]

bb mentioned an expansion joint, i probably won't be able to do this, at least not at the location where the wood subfloor transitions to the concrete (which is just a mass of concrete that was installed to receive the old hearth stone tile). removal of the plywood that was put on top of this concrete isn't an option, i planning to put furring (nailers @6" oc) over this, then using a self-leveling fill between the furring strips to bring this up flush with the top of the furring then install a thin sheet of plywood to flush out the substrate surfaces. (there area here that i am talking about is 48" x 30")

should i consider installing a crack isolation membrane (eg noblecompany CIS membrane) over the 1/2" hardiboard.

also, before i install the hardiboard on the new 3/4" plywood, should i apply something like paint or a waterproof membrane to protect the plywood from the thinset that is recommended between it and the hardiboard?

thanks

donq