Please help Tiling over old flooring

My house was built in 1961, it had old carpet in my home, and I decided to remove it. Under the carpet it revealed vinyl tiles as the previous "finished floor". These tiles are secured with mastic, on top of a couple layers of plywood, I believe the thicknesses are 1/8", then 1/2", it's difficult to measure due to the multiple layers and having walls in the way. Under these layers, the original subfloor is shiplapped planks running diagonally throughout the house at a thickness that is unknown and impossible to measure. I plan on tiling over this floor as the new finish, my father had brought over 1/8" mahogany plywood to seal up the old flooring and provide a somewhat leveled surface to tile over with the idea that if the floor needed to be leveled beyond that, then we would use self leveling concrete. The mahagony plywood is secured with 1 1/4" brad nailer staples. This did
Tie in the floor better than previously, however I stopped the project when I noticed a squeak in the floor and began driving deck screws in attempt to tighten up the spot. Now I find myself in a position where I am worried whether or not this would be suitable to tile over. I have no problem laying down a tile membrane over top of the mahagony of need be. I expressed this concern to my father, his logic behind the choice of the 1/8" mahogany is because I the multiple layers my floor already has and the floor has minimal deflection because the floor has plywood over top of the diagonal planks. Now I am at a point where I am questioning whether this will be secure enough for the tile, and I don't want to have to rip up what I would have done, to only solve the issue by doing what i felt should have been done in the first place. The squeak I believe is coming from a floor joist in the basement, which I will add blocking to, In attempt to eliminate the squeak. Am I alright with these multiple layers, with a tile membrane, or should something else be taking place here, my father seems to be pretty confident, and he has remodeled multiple houses over the years.

 

Even 1/4" plywood has no place in a tile installation, it's too flimsy. I would strip back to the 1/2" layer and re-evaluate.

What's the size, spacing and unsupported span of the floor joists?

 

Hi Spadaforet,

Thank your father for helping, but tell him you've done some research and found your current plan leads to failure. It's not a good plan for any flooring, but it's especially bad for ceramic.

OK, let's start over. Built in '61, I'll ask you about the joists in a minute. The subfloor is 1x4 or 1x6" boards laid diagonally. Then either ½" or could be ⅝" ply, then you probably have luaun ply with the vinyl bonded to it. You said it's ⅛", but it's probably just under ¼" .

It's confusing whether the new ⅛" (?) ply is fastened or not. (Hopefully not).

You probably guessed what coming next, but yes, you need to remove everything down to the ½" ply over the subfloor. Sorry.

Tell us the size of the joists, their spacing, and their unsupported span. It would be helpful if you also knew the exact species and grade too, but I'm not gonna hold my breath on that.

Jaz

 

Your father is probably right, the subfloor has minimal deflection, especially with 1/2" plywood.
In my home I have a 2x8 subfloor, no modern "joists", the span is further. Still it's going nowhere.

Just wanted to agree with Jaz, the floor would probably be fine to install tile if that extra layer of Luan wasn't added under the vinyl tiles.

 

I appreciate the quick responses, thank you very much.

I'm not at my house at this exact moment, but what I can tell you is that the joists are pressure treated spruce 2x10's, 16" on centre, 14.5" in between each. I have a big fat metal I-beam which supports the load above (Single storey, bungalow style home with hip roof) surplus from the mines from when the house was built. As for The unsupported span across each side of the beam, I'm not sure off hand right now, but I can get back on that when I'm back at home and I can measure.

I'm sorry if I wasn't so clear in my post, but some of the New ply has already been secured in some areas where I intended on laying the tiles.

I understand the concept of using thicker plywood as a good subfloor, but what needs to be understood is that if I can avoid removing those old vinyl tiles, that would be preferable. What I want to know is, (and I realize the disadvantage of increasing the height by adding layers), if I can remove the new plywood
and put a thicker plywood to satisfy the need to secure the plank subfloor (which, after reading, I believe to be 1x4...) or am I completely screwed? Thanks again. If you have any more questions about it, let me know, I really appreciate it. I'll measure the span from the support beam to the exterior walls when I get home if it's still needed. The layers under the tile do not contain luan, I was mistaken the dimensions, I apologize, the floor consists only of tile being adhered to 1/2" plywood, with the lapping subfloor underneath, with newly installed 1/4"**!! Mahagony on top. I was corrected when I spoke to my dad about it. My apologies for the aforementioned 1/8" dimension, that is incorrect, it's ' 1/4" '....

 

What we have here is two competing realities that you are trying to make work. You want tile but in order to get tile, you have to properly prep for that tile. The mix you have doesn't create a satisfactory base for tile. Perhaps you can think of another type of floating floor such as an engineered hardwood or bamboo. Tile is a unique animal in that success requires some pretty stringent rules be followed. If you have squeaks now, it says you have movement which will cause a failure. Thickness derived from multiple layers does not equate to structural strength. Further, you can not simply use self-leveling compound on top of plywood without the use of a wire lath for it to grab onto. Further/Further, subfloors and underlayments are not put down with brads - You use Crown Staples or 8d ring shank nails - but that is a mute point as the thin layers need to go.

 

They were crown staples installed with a brad nailer. 1 1/4 16ga? I believe.

After walking on the floor, bouncing on it, looking at the joists, coming back up, I'm not actually feeling any movement.. I believe it could be a shrunken joist, (everything was nailed in place, not screwed), because the location of the squeak comes from an area where the furnace had been framed in with double headers, and it might be possible that these boards have less moisture content than the rest. I'm going to provide extra bridging to these joists to see if that will mitigate the squeak itself. But yes I do share the idea that simply sandwiching layers of plywood together doesn't make one theoretical sheet of plywood.

 

I was under the impression that metal reinforcement is for tensile strength. I don't see how metal lathe would aid in the chemical bonding of wood to cement. In any event, there is no area on the floor that would justify adding a layer of metal lathe to make it level. If any compound would be used, it would be for the most minute difference in elevation. I figured using a primer would be the way to go in terms of strong chemical bond between the two materials. The only difference in my opinion lathe would provide is the tensile strength of the "pour" if I can even call it that, and if the lathe was fastened to the plywood, then the concrete would benefit from the bond yes, but not to the wood, but to the metal itself as it seems to react better to metal than to wood. But like I said there is no justifiable way to use the lathe in my situation, I would actually have to go out of my way to use it, because the only way at that point would be covering the whole area just to use it at all, which wouldn't make sense to me because this far, there is minor elevation difference from one point to the next.

 

Read the installation instructions on Self Leveling Compound to understand its limitations. It is not approved for use over wood of any kind without a mechanically fastened wire lath to give it something to grab. Cement, mortar, thinset or what ever does not bond with wood, there is an intermediate needed (cement Backer Board) in order for the mix to last.