Advice on type of floor leveling compound

I'm laying 12" x 24" ceramic tiles over 1" of plywood subfloor and 1/4" of cement board. The 1" of ply is made up of two 1/2" pieces of plywood laid with perpendicular grain.

My method is to use thinset over the plywood before laying down the 1/4" cement board afterwhich I'll put screws every 6-8 inches.

The floor sinks maybe 1/4" at the deepest point. What kind of floor leveler should i use to bring the floor to level before attaching the cement board? I'm not sure what will work best with the thinset.

Help is appreciate. I really only have access to Home Depot and Lowes, so any brand names particular to those stores would be appreciated.

Thanks

 

A couple of things you should be aware of. First, two layers of 1/2" plywood is not a suitable subfloor. You should remove the second layer of 1/2" ply and install at least 5/8" or 3/4" plywood. Second, any leveling that you need to do happens on top of the cement board, not under it. You mention level, but the floor doesn't need to be level, it just needs to be flat. If its flat, you don't need to make it level unless you want to.

 

HeresJohnny,

Thanks for the reply. The only way I could do as you suggest would be to rip out the entire shower base which I'm not willing to do. There are other reasons why replacing the subfloor would be a huge undertaking but I'm trying to be brief.

A few inches under the subfloor is concrete. About every 8 inches an adapted 2x4 was used between the concrete and subfloor so it's well supported. When I put the second layer of 1/2 plywood over the top, I was careful to screw through both layers into the 2x4s below.

I was wrong to say level. I just want it flat.

So you're saying lay the cement board down FIRST, then level it prior to laying tile? In this case I should use thinset as the leveler as well as the way to bond the tile to the floor? If so, I would have to level it with thinset, let it dry, then use thinset again to adhere the tile to the floor, right? Is there any problem with thinset adhering to thinset? Do you suggest a different leveler?

 

If anyone out there can just give me some advice on what kind of "leveler" to use over cement board that would be much appreciated as I'm in the middle of this project and I don't necessarily trust the advice I get from the big box stores.

Can freshly prepared thinset bond to thinset that's already set for a day? How thick can I do a layer before letting it dry and adding another?

 

I question your build up over the slab and the ability to get a solid enough sub-structure to tile. But that is not your question.

Install your cement backer board in a bed of thinset mortar. Then prime your backerboard with SLC primer and then float your primer. Any SLC will suffice, you just need to prime it first. HeresJohnny mentioned that in the first reply.

 

czizzi,

HeresJohnny also had the same concern about the underlayment. I know a tile guy and he's going to swing by next week to give his on-site opinion. Thanks to you and HeresJohnny for the red flag. I still think it's okay given the 2x4s ever 8 inches underneath but I'm just an amateur.

I'm not sure what "float my primer" means. I'm guessing this is the trade way of saying apply the primer (leveler?) with a float. Maybe this will make more sense when I check out the actual primer.

If the floor isn't level, wouldn't using a Self Leveling Cement set in a way that doesn't make the floor flat? I've done two small tile jobs before but never used a leveler so sorry if that's a dumb question. I was expecting something like thinset but I'm guessing now its' more of a liquid? Again, I'll try to take a closer look at the product.


Strange, I didn't and don't see anything from HeresJohnny about that but I'm glad you came along. I only see one post from him on this thread.

Thanks for the help and advice.

 

To be totally honest, I don't think it will matter much what you do. The subfloor build-up is a recipe for disaster.

 

HeresJohnny said in his first post that the leveling happens on top of the cement underlayment. So he gets nods to the first to suggest the correct procedure. SLC is not a robot that does what is is supposed to do, so my statement to "float" the SLC was meant to say that you just can't pour and walk away. You need to stay with it and massage. It will slump when poured, but will not necessarily flow to a perfectly flat surface on its own, you have to massage it. So, while it takes 20 minutes to set up, you have to set there the whole time to "remind" it that is is supposed to be flat. Test a small area to get use to my procedure, you'll see what I mean.

 

Peter,

The problem with your method is you're installing a "sleeper" floor over concrete, AND it's below grade to boot. Bad plan, it's not recommended by anyone who knows much about these things. But, it may just work anyway. How long before it fails? No one can tell you, 1 year....maybe 20?

SLC might be the wrong way to make this floor flat. It all depends on how much out of level the floor is and how large an area is not flat. You could end up with a build up much thicker than you planned. Thinset is not a good choice for making a floor flat unless it's just a small area and very shallow.

Me...I'm shakin my head with this.

Jaz

 

Ah, that's what you meant. Yes, he certainly did.

I didn't know about the massaging as I've never worked with stuff. Thanks for your patience to explain further.

 

Look, I know how it is. People come here all the time thinking their method is the exception to code or the rules and they are quick to tell the pros why they are wrong. On the other hand we DIYers and even contractors sometimes need to deal with unusual situations and apply common sense and make choices within realistic parameters. In my case, the expense and effort it would take to create the perfect underlayment as you describe would mean it wasn't worth doing and I'd lay something like LVT instead.

I don't expect anyone here will recommend anything other than what's known to be acceptable. That's a slippery slope. But still, what's the thought process behind 1/2 over 1/2 NOT being acceptable, but 1/2 over 5/8 is fine? That 1/8 of an inch is really the difference between a project being just fine verses it being a "a recipe for disaster" as some have said?

As I mentioned, then 1/2 on 1/2 subfloor has 2xs at LEAST every 8 inches supporting it underneath and I made an effort to screw through each board and sink into those studs. I may not get anyone here to say it, but to me that's going to be at least as strong as 1/2 + 5/8 going over studs 16" on center. I'm open to further comments on my reasoning and as I said, I'm having a pro stop by next week to give me his opinion before I go further. If I didn't value the advice here, I wouldn't be posting. Maybe you could tell me what is meant by a sleeper floor and why that's bad. Does it shift more or differently when mounted to concrete as I described?

I don't think the floor dips by more than 3/8" at any point. The area is a 4x4 bathroom that opens into a sort of pantry that's 12 x 6. I might be able to rip out the 12x6 underlayment in the 12x6 but not the 4x4 space. I'll wait for the pro to comment before I get into more detailed descriptions as everything might change.

Thanks for the advice!

 

I didn't mention the two layers of ½" ply because as you said that is not the problem in this case.

I'll assume the 2x4's have 8" of space between them, making them about 11.5" o.c. if laid flat and not 8" o.c. That floor is plenty stiff enough. Even a single ⅝" woulda been plenty. While we're on the subject, it was mentioned that two ½" layers does not a good subfloor make. That is true under normal conditions when the joists are 16" o.c as you said. Matter of fact, a single ¾" subfloor is stiffer than two layers of ½". But that's not what we're dealing with now.

The problem is your wood floor system below grade. The humidity can cause the wood to shrink and expand way more than any finish floor can handle. You're also strapping the moisture which will make it worse.

As far as 'will it work?'. This system has been used for many years, and sometimes it works ok for a long time. You will not find this method in any book as it's not a good practice that any pro can recommend.

Jaz

 

JazMan,

It's more like 8" (or less) on center, but the 2xs are upright so the 1 1/2" side is what contacts the first layer of 1/2" subfloor. I actually used liquid nail to secure the 2xs to the concrete floor. I don't know if that was a stupid, but I'm sure someone will let me know. Other than being glued down, the 2xs are not anquored to anything else, but wait... there's more..

It's a small bathroom with a toilet, sink and shower. The part I'm tiling is about 4x4 or a little bigger. The floor was raised up under the toilet such that there's about a 2.5 x 2 slab of concrete. The way it had to be done to keep things level with the hallway next to the bathroom, I ended up putting 1/2" ply on top of the concrete slab. In other words, the first 1/2" ply that sits on top of the 2x4s brings it level to the concrete slab that holds the toilet. The, I put another 1/2 ply on top of the first 1/2" and then extended it over the concrete slab. I then secured the top 1/2" piece of plywood to the concrete slab using tapcons.

If I raise the floor anymore it will probably mean cutting off the bottoms of two interior doors and one storm door heading out to the backyard. One of the interior doors goes to a closet which I don't plan to tile and which would then be lower than the rest of the floor.

Fun project huh?

 

Gee, lots of errors here.

If you wanna rip it all out and start over let us know.

Jaz

 

Have I questioned your knowledge or intelligence or tried to pretended I know better than you? Have I been rude or unappreciative of your help in anyway?

If not, then why take a condescending tone with me? I worked in a hardware store for many years and I enjoyed helping people. If it's not your thing, that's fine, but then why come her to a place where you know amateurs like me are going to come to seek help?

Please don't bother to comment on my problem anymore. If out of some twisted form of solidarity this means others won't help me here either, then so be it.

 

I understand to flooring is usually over joists but this is a basement so one way or another this floor will have to rest on concrete. I don't understand what the concerns are for moisture or swelling or how to avoid them. Even if I rip out the 1/2 ply and replace it with 5/8 or 3/4 as was originally suggested, it will still be over concrete. As I described below in this thread, they poured a sort of slab just under the toilet. I also don't know if I should be using liquid nails, trying to secure the base to wall studs or leaving it alone in some way for expansion.

As I said, I've heeded your advice and have stopped going forward until a pro comes out this week. Unfortunately, it was "pro" who lead me to believe the floor would be fine in the first place, so it's always good to get a second opinion.

Thanks!

 

You would be better served to build your tile floor directly on your concrete and do away with the sleeper system all together. As many times as we have seen these sleeper set ups over slabs, there always are complications that ruin otherwise good intentions down the road. Tile likes solid stable surfaces. Any moisture in the slab will cause major movement in the wood members underneath. Liquid nails as the attachment medium will only last for a limited amount of time as that is not what it is designed for. Over time, any movement will cause your floor to fail. We can not in good faith tell you this is a good and solid long term proposition to move forward with. Please take this under advisement and not as a point of contention. We are trying to help and are saying that the set up you have is flawed.

 

czizzi,

Thanks for the reply. The area I'm trying to tile is in a bathroom. The original home owner poured a concrete slab under just the toilet and used a sleeper setup for the rest of the room bringing it up to level with the concrete slab. The bathroom area I need to tile is about 4x4 and joins another 12x6 area that's also raised and can't be lowered do to having a closet and a door going outside to ground level. (I live on hill, so basement is exposed on one side)

If I'm understanding you right, the only acceptable solution would be to pour concrete for the rest of the bathroom and the remaining 12x6 area, then tile on top of that once it cures and other preparations are made. Is that what it comes down to? There is no wood frame solution that's acceptable regardless of whether it's attached to the walls studs or if I put down an vapor block or anything like that?

With all due respect, this entire thread is a testament to me understanding that. At one point I literally said "I don't expect anyone here will recommend anything other than what's known to be acceptable." I've taken the warnings seriously, stopped work, and called in a pro. The two layers of ply are already down. The only reason I've been taking all this time to explain all the details of what's under it is because I'm trying to determine what's wrong and how to fix it and I've only done all this because I've taken the warnings seriously.

Thanks for setting me straight. If it really is the case that pouring concrete is the only truly acceptable solution, then I'll need to reconsider the whole project. LVT and linoleum maybe aren't so bad after all. lol.

 

Boy oh boy, you are very sensitive.

What's wrong with saying there's lots of errors and it would be best if you could start over?

Go ahead and do it anyway you like regardless of what advice you find here.

You got that info from a pro? There you go...... So, if another pro tells you the same thing what does that mean? I told you it might work anyway. Good luck.

Jaz

 

Can the additional slab that is under the toilet be removed so that you are down to the original concrete all at the same level? That would, in my opinion, be the optimal solution. There must be a reason the additional slab was poured around the toilet that we are not aware of.

 

czizzi,

Of course I could remove the slab, but I'm pretty sure the reason the toilet was raised in the first place was to create a downward grade for the drain. It's already touchy and I've had to rent an auger on a few occasions to clear clogs. Good suggestion, but I'm not willing to risk losing the toilet. Also, an exterior door going out to the backyard patio are on the same level as the raised floor.

Well, I think I have a good idea what my options are at this point. If there was a way to use a moisture barrier or to do something other than a sleeper floor, I'm sure someone here would have told me by now. I'll see what the tile guy says when stops by but it doesn't look like there's a practical way forward.

Thanks for your patience and advice. I think you guys have done all you can for me at this point.

Thank you