Question about advice from tile installer

My house is on a concrete slab. In remodeling after a fiew, the living area was extended into one end of the garage (ell) and down one side of the garage. Those extensions are floored with plywood (1"?) on joists to be level with the cement. I am using ceramic tile throughout the house. The installer says to take out the plywood on the joists in these extension areas and reduce it to 1/2", over which he will lay cement board, then "float" the tile over the transition, gradually tapering out 4-5 feet, and he "thinks it will be okay." Everything I've read tells me that 1/2" plywood is not going to work, and there will be cabinetry and filing cabinets on the wood area, and the length of the transition line is high traffic. Help, please!

No, it won't be ok. How much of a drop off was there from the main living area to the garage slab?

Also, seems you knew the answer before you even asked. Is there some reason why you didn't just say, "Thanks for your time," and show him the front door?

Hi Ann,

Somebody should have planned this better. Didn't you know you were installing tiles when the addition was built? Definitely tell the tile guy, (is he really a real tile setter?), to re-think his idea to replace the ply with 1/2" ply. If he says it's OK, show him the door.

Why did he say to taper out 4-5 ft. If the two areas were going to be the the same level after changing the ply and adding the 1/2" CBU? What am I missing?

If indeed both areas are the same level AND built correctly, all you need to do is install Ditra Membrane on the entire area and then set your tiles.

Jaz

Call someone else

Thank you so much for your responses.

You're right that I am worried, but I only know what I've read and have no experience, so I am a bit intimidated in dealing with trades people.

It was known that tiles would be installed but apparently what was required for subflooring was not known!

This is a small house. The ell extension is 6 X 11 1/2. The extension down the side is about 2-2/1/2' (I don't have the exact info here.)

The garage is lower than the living area by 1 to 2 '. The framing for the extension floor was was built up from the garage floor. With the one layer of plywood on top of the joists, that area was about level with the cement slab. So even taking it down to 1/2" plywood, with cement board on top, it's still going to be higher than the cement.

The installer is saying he can "float" the tile over the transition in heights, gradually tapering off the distance. I think it's a leveling compound this would be on -?

Is it an experienced carpenter I need at this point? Probably the framing under that whole extension should be redone? But there is already a finished wall between the garage and living area (partitions, door, the whole bit, sheetrocked). The tile is already purchased.

Do you see any solution? It wouldn't work to make a step-down level for only that 2 or 2+ feet, but if the wood flooring level could be brought out further on the cement some way, a step-down would be logical about 8' from the wall.

Any guidance you can give me will be appreciated!

Annie you are getting some bad information from this tile guy. Most areas of the country have a minimum thickness requirement for a subfloor of 5/8". THAT, is an absolute minimum set forth by the "Uniform Building Code". The key word here is "minimum". Most builders build to minimums to save money. To remove a substantial subfloor and replace it with only 1/2" material subfloor would be a disaster.

You don't mention your joist spacing. The space between the joists is also critical in the performance of any subfloor material. Joist spacing and subfloor thickness is super critical when it comes to a tile installation. THERE ARE RULES!

If you now have a subfloor that is 1" thick, leave it alone.

You should also be aware that NO cement board tile backer offers any structural value - none what so ever. Cement board is nothing more than a suitable tooth for the adherence of the tile adhesive. To think that cement board values are a replacement for wood subfloor values is just plain wrong. Don't be fooled by the the word cement. Cement boards are not anywhere near the same thing as cement/concrete floors, they aren't even in the same league even tho they sound the same.

Something else you should be warned about: Installing ceramic tile transcending from wood to concrete is problematic. The two materials do not expand and contract at the same rate. That juncture could easily disrupt a hard tile installation. The only procedure that lends itself to some comfort is to isolate the tile installation from the substructure totally. This could be realized with a product such as Schluter DITRA or an old-fashioned mud job separating the tile from the subfloor.

I'm thinking you need a different tile guy for sure. Find one that knows the rules and understands the basics-it's not this guy for sure.

Thank you,Bud. I thought maybe no one was responding to my second post because I am not doing the work myself (I'm pushing 70, with health issues.)

I needed this info! I've been wondering if 1/2" is even legal and if cement board is structural. And I'm glad to know about the Ditra being called for in this situation (Jaz also mentioned it). I have been reading here, but wasn't certain which situations called for which materials.

I have a couple more questions, but I will measure tomorrow to be sure I have it right before asking.

And by the way, the advice came from "the" installer for one of the long established flooring retailers in town and has done a lot of tiling. By way of explanation, I am waaay in the boonies.

Thanks again.

Just because you are in the middle of nowhere doesn't mean you need to settle for an "I think it will work" solution. Ditra over both areas will work but you would want to honor the change of substrates with a soft joint, which would be a color/texture matched caulk used in place of grout at the doorway. Ditra would add about $2.50 sf to the overall install.

I'd asked about the height difference because if the floor was 2x4's on their flat side with plywood on top, then a mud job over the slab would have fixed the problem, but not at 2'.

He could use 1/2" underlayment plywood with 1/4" cement board and yes, it should work just perfectly if he floats the 1/2" plywood over the joists on a sunken subfloor. This is certainly not what he was intending to do and material and time wise, Ditra would be much less money. There is one more thing you will need to check about the plywood you have, though, to see if Ditra will work. I'll explain both.

A sunken sublfoor can be used when additional floor thickness of structural plywood is needed but height build up is limited for whatever site conditions exist, for example, in your case, the plywood subfloor is level with the existing slab.

To sink the subfloor, cleats of 1x's are installed along the floor joists 3/4" from the top of the joists. The 3/4" subfloor panels are then cut to fit between the joists and attached to the cleats. Next, a belt sander will take any crowns in the joists down so they are all in plane with the surface of the 3/4" plywood. After that, underlayment rated plywood is installed over everything, fastening it only to the subfloor panels, not the joists. Then cement board can be set in thinset and screwed down, with everything there now all at the same height as the adjoining slab.

The only way either ditra or cement board could work over a single layer subfloor anyway would be if the subfloor panels were tongue and groove plywood, so that the adjacent plywood panels won't sag where they cross the joists as they lock into one another. If the panels are square edged, then there needs to be framing between the joists to support the panels where they cross the joists. If there is visible space between the subfloor panels and you can poke a putty knife through them without it stopping, you have the wrong subfloor anyway, you will need minimum 3/8" plywood anyway then cement board. If that indeed is the case, the installer could use 1/2" plywood on the existing plywood area, then do a 3/4" thick mud job on the slab area, or, revert back to the sunken subfloor idea.

Thank you for the additional information and advice.

I checked measurements yesterday. Besides the 6 X 11 ½’ ell incorporated into the living area from the back end of the garage, the strip down the side also incorporated extends 35” from the interior wall.

The living area is about 11" higher than the garage floor (doesn’t seem to be consistent by 1/2" if I'm measuring right).

The original subfloor was ¾” plywood (not 1” as I thought – I apologize for not having this right and misleading you about the situation I’m dealing with – hope you will forgive me that, when you have been so patient in advising me). It is this ¾” that was level with the cement. That plywood was removed and partially replaced with ½” plywood before I called a halt.

The wood under the ¾” plywood is not on its flat (widest) side. The framing is raised from the garage floor a couple inches. The carpenter says that while the original plywood was off, he doubled the joists and added “nailers” -- what I understand the nailers to be, from reading here and his description, is wood braces lodged between the joists.

Someone has suggested (as I understand it) repositioning the joists to be lower (maybe to rest on the garage cement floor?), topping them with ¾” plywood, and pouring 2 – 3” concrete on the plywood to make the subfloor all the way through cement. Is this a good solution?

If that’s not a good idea, is the sunken subfloor the best way to proceed? Or do I use one subfloor done in tongue and groove plywood (I’m thinking my mistake in saying the original was 1” instead of 3/4” might make this unworkable)? Or do I layer plywood (what depths? ¾” and ½”?), and if so, would the increased difference between wood and cement floor heights make it necessary to have a step down someplace (logically, it would be about 8’ from the wall)?

Is it best to use the Ditra in all of the above situations?

Also, when I said the plywood should be exterior grade, the carpenter asked what that meant and told me that pressure treated plywood should not be used. What was purchased was CDX plywood. Could someone please tell me what CDX means and what exterior grade means?

Again, thank you.

By way of explanation, I am waaay in the boonies.

The (tile) installer says to take out the plywood on the joists in these extension areas and reduce it to 1/2"

When I said the plywood should be exterior grade, the carpenter asked what that meant

By any chance are their maternal grandparents also their paternal grandparents?

Exterior rated plywood means the glues for the veneers are rated for exterior use, so that when the house is being built, it won't fall apart on a rainy day. The "X" at the end of the letter code for the plywood means "exterior" it is also listed sometimes as "exposure 1"

The first two letters, and you pointed out they have CDX are the quality of the face and the veneers. The lower the letter, and they go from A to D indicates the quality, with an "A" face plywood being furniture grade plywood face and with each higher letter, larger imperfections, knotholes and voids are allowed in the layers. CDX, also known as "Sheathing rated" is the lowest quality and is only for sheathing the outside of a house or roof for nailing siding or shingles and it's not to be used under a tile floor ever.

If you have 3/4" plywood, that is 3/4" t-g plywood subfloor panels glued with construction adhesive to the joists and nailed or screwed, then Ditra is your best option. Anything else is probably too involved for them. If they put 3/4" CDX as the floor, then it's no good, and they are cheaping out on you. Probably would be fine under carpet or laminate, but not tile.

Thank you very much for explaining plywood ratings. I am beginning to wonder about the grandparents too!

The 3/4" plywood was not t-g and not glued. Are you saying that if I replace it with 3/4" t-g, making sure construction adhesive is used in addition to nails/screws, and cover it with Ditra, I truly won't have to worry about future problems -? I thought the depth had to be at least 1 1/8 -? The Ditra would be used on both the wood and cement, right?

PS addition to last post: I take it that the cement idea mentioned 11/4 is a bad one, and the most feasible option is the Ditra matting, which I believe you are all saying should go through the entire house,correct? (+ caulk instead of grout where the wood subfloor meets the cement subfloor)

If it's the entire floor, at $2.50/sf for about 1000 sf, the mat itself would cost $2500. (Guess I won't be taking any trips for quite some time, so I'd better like what I have at home!)

Aside from the Ditka, grout, caulk and sealant, are other materials still needed when using Ditka? Leveler or whatever? (I'd like to know what I should be looking for in the plan and billing.)

If you think I am insecure about this, trying to double check everything, you are absolutely right!

Thank you once again.

Hi Anne,

As a female and an installer I recommend you leave the plywood in place and use an anti fracture membrane over the whole floor.
[Schluter.com] has a product called Ditra Mat, and it is what is called an uncoupling membrane, which means, even it releases from the substrate, the tile will stay in tact.
If it is used you must use an unmodified thinset to install the membrane as well as the tile.

If you are in Florida, I will be happy to talk to you further. It sounds like you are not having good luck with sub contractors.

Linda
aguiarfloorcovering@yahoo.com

If the 3/4 subfloor they installed is square edged CDX plywood, it's wrong, needs to be replaced with tongue and groove subfloor rated plywood. If it's square edged plywood, but underlayment rated, which would be better than CDX, it's ok to use it if, as I described before, it was both glued and nailed or screws and they installed solid blocking between the floor joists to support the subfloor panels where it crosses the joist bays.

We've already established that Billybob and Jimmyjoe did not install it properly nor did they use the correct grade of subfloor.

If they install the correct plywood subfloor, fastened properly:

1) 3/4" tongue and groove plywood subfloor panels

2) subfloor construction adhesive beads are used along each joist prior to placing the subfloor panels, 1 bead if a panel is crossing the joist, 2 beads if two panels will join on a joist.

3) Long edge (face grain) must cross the joist, not fun parallel to the joist

4) panels are to be staggered so that no 4 corners come together and there is to be a 1/8" gap between sheets

5) the minimum fasenter pattern is every 12" where a panel crosses a joist or every 6" where a panel ends on a joist.

6) joist 16" oc and deflection not to exceed L/360

Then Ditra could be (not Mike Ditka ) can be installed over everything.

As a female and an installer I recommend you leave the plywood in place and use an anti fracture membrane over the whole floor.

If it is used you must use an unmodified thinset to install the membrane as well as the tile.

Umm, no, if used, you would use a modified thinset over the plywood to set the Ditra and an unmodifed over the slab area. Then an unmodified to set tile on both.

Annie, unfortunately, your floor isn't built for ceramic as it is anyway. They need to ensure the subfloor is constructed using the minimum standards I listed above.

Bud asked about the joist info earlier, I don't recall seeing it. Provide the joist size, spacing between and how far they span between supports and we can figure out #6 above.

If you have 1000 sf of tile going in, there are other considerations as well. Interior tile work is to have expansion joints every 20-24 feet. This is done by using a color/texture matched caulk that looks like the grout in the grout joint at specified intervals. If you can throw them in doorways, then they aren't as noticable being they aren't that long.

What is the condition of the slab in the house? Are there any cracks or expansion or saw cut joints?

Back to the garage, how many total square feet is it? Another underlayment option is NobleCIS. Installed it's only 1/16" thick and if the slab is in fine shape in the house, you could do CIS on the garage floor area of plywood only. 1/16" is within tolerance of the in plane variance of a to be tiled floor and if there are no cracks or other issues in the house slab, it would eliminate the need to cover the rest of the living area with a membrane.

Lastly, threads close after 20 replies so when this one hits 20, just start a new thread entitled "Annie's garage, continued"

I do understand I need to replace the subfloor in the wood section, and I thank you for taking the time to give me specific information about how it should be done. The only point I don't understand is the meanig of allowable deflection -?

I am glad to know about the expansion joints needed throughout, in addtion to using the caulk where the cement and wood meet. Should the tile be laid such that the caulk line runs precisely over that meeting place?

I went over there today, thinking I could measure the joists, but the ell part (taken from end of garage) is still covered with the 1/2" plywood, as is part of the 35" strip down the side. I will get that cleared out so I can give you better information.

In the 3' part of the 35" strip I could see: There is a board 7 1/4" x 1 1/2" along the wall next to the garage (1 1/2" side up), beginning about 3" up from the garage floor (I could not see what was supporting it). Nailed to that board, flush with the top, is another board 3 1/2" x 1 1/2" (1 1/2" side up). There are 3 more single 3 1/2 x 1 1/2 boards at the same level as the first, all running parallel to the wall next to the garage, with the last one along the living area cement slab. I did not see any support running between them. More info to follow when the 1/2" plywood comes up.

There are no cracks in the cement in the living area. The garage cement, about a foot lower, does have a few cracks, one of which runs close to the living area. I will check under the ell section when that plywood comes up.

The cement in the living area is not smooth like new-poured concrete - it's bumpy. I know some high areas were taken care of awhile back -- but I should check with an actual level, right? Where the concrete meets the wood, it has a ragged edge, if that is significant. The cement is all one piece. Is this considered good enough shape not to need the Ditra, or would using the Ditra be safer?

What is the difference between modified and unmodified thinset? You mention using modified over plywood, unmodified over slab.

The saga continues. (Billybob and Jimmyjoe are the anti-heroes.)

THANK YOU!

PS The distance between the 3 1/2" and 1 1/2" flooring joists described above varies - 8 3/8", 11 1/4", 7 5/8", with the 11 1/4" being in the middle.

Finally, I have more specific info about the floor framing, which does not, to my untrained eye, appear stable.

[Reminder, 'cause it's been awhile: When remodeling after a fire, the living area (on a concrete slab) was extended into the back end of the garage (that ell is about 6 x 12') and down the side of the garage (3' strip). The garage cement floor is lower than the living area slab by about 2', and it slopes down to the front. It's the floor framing in the ell and side strip (formerly part of garage) that I'm talking about. The finish floor will be ceramic tile througout the small house.]


In some places the sides are fully resting on a cement sill, but not all. On the side of the ell towards the garage, there is a 2 x 8 that really isn’t supported by anything except the cross joists which are in turn supported by the arrangement described below.

From the living area to the end of the ell, there are 2 x 8 joists going across, spaced 12” and 16” oc. On the outer side (what was the back end of the garage), they are hung over the cement sill with notches half way down them. Isn't that too much weakened?

Underneath the joists going across the ell, apparently for leveling, there are pieces of 2 x 4 here and there (no particular pattern) lying on the 4” side against the cement, many with some wedges (even the occasional skinny piece of scrap wood) on top of them as shims under the joists.

Along the living area slab, there is a 2 x 8 resting on a concrete “ledge” which appears to have been chipped out of the slab (or a separator?), but the ledge is so bumpy the board and concrete are not in full contact… there are significant gaps (up to at least ½”) between them for long stretches.

On the outer wall of the strip (toward the garage), there is a 2 x 4 directly on cement (on 2” side), then another board overhanging that by an inch or so, then two boards with sides butting on top of all that overhanging by another inch or so. Doesn’t make sense to me.

Also, although there are no cracks in the slab in the original living area, there is a crack in the cement in the portion of the garage incorporated into the living area – a gap of ¼ to 3/8” wide, running crookedly for about 3’. One side of the crack begins butted tight to the cement which separates the higher living area slab from the garage slab, while the other side of the crack begins ¼” or more away from that separator. It appears that the tight part buckled.

This whole thing can't be right, can it? Am I right in thinking I need to have all that taken out and start again? I would appreciate any guidance you can offer, as I would like to be sure it's done right this time. And again I thank you for your patience and help.

I don't know what kind of wood is there. Some seems to have a lot of knotholes. Some (not much) appears to be treated (darker).