Before installing tile on your floor you must make sure your floor is properly prepared.  A properly prepared floor does not have to be level. It must, however, be flat.

The only time the levelness (is that a word?) must be taken into consideration is when drainage is an issue, such as on a porch or in a shower. In those cases you must make sure your floor is not level – it has to be angled toward a drainage area.

If your floor will not be subjected to water regularly, such as a kitchen or bathroom floor, it does not necessarily have to be level. That does not mean you can have a 45 degree angle from your door to the cabinet (although I suppose you could if you wanted), it just means if your floor is not absolutely level it will not negatively affect your tile installation.

One of the things you must make sure of, among other things, is that your floor is flat. If it is not it will be difficult to set your tiles without what we call “lippage”. That’s a ridiculous word, isn’t it? Lippage simply describes the difference in the height of two adjacent tiles. If you have a tile that sticks up higher than the tile next to it you have lippage. You don’t want that. Starting with a flat floor helps prevent it.

When prepping your floor for tile trade your level for a straight edge. Don’t be concerned with how level your floor is, be concerned with how flat it is.

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  • AR

    Hi!

    I have a bit of a difficult question for you (in my opinion!). I’m about to tile a bathroom (90+ years old). The floor slopes approximately 2 inches over an 8 foot length. The possibility of levelling is impossible because of a door on the low side that would cause a drastic transition. Thus the plan is to create a flat surface for the tile.

    This brings me to my actual question. The original hex tile was laid in a wet mortar bed ~3″ thick and I plan to tile overtop of the tile (this wont raise the floor a substantial amount and therefore wont mess with the radiator and toilet flange heights). Is using a sand mix concrete to level appropriate if I will then be using ditra as an uncoupling membrane?

    Reply
  • Rici

    BTW…our living room is 23×21 and only 1/3 of the way finished. So wondering if we need to prep the leveled floor somehow before proceeding further.
    Thanks,
    Rici

    Reply
  • Rici

    Hey Roger,
    I had a “tiler” bust out tile throughout my home about 1000sf +/-. He then said he’ll need to put leveler (28 bags total) and laid about 1/4 of the tile and walked off the job!! MIA…my new tiler asked me yesterday if he used primer before pouring the leveler on?? I’m sure he didn’t bc I didn’t pay for it when I paid the $900 to Lowes. Do you think this is a huge issue?? My new tiler said he’s never used leveler without primer and our tiles may lift in a few months…:(
    Thanks,
    Rici

    Reply
  • Denis Blaquiere

    I live in SW Florida and hurricane Irma recently paid us a visit. Our Florida room used to have carpet that the prior owner installed but we ripped it up a couple of years ago as it had gotten real funky being exposed to wind driven rain (tropical storms and hurricanes). We figured now was a good time to lay some tile but my question is that there is a residue of the old carpet glue covering the entire floor. I thought it was stable but after a good soaking by Irma some of the glue “bubbled” up. It scraped up no problem. Do I need to remove all of it or will the thinset work over it i.e., setup ? I have gotten conflicting opions from different tile stores and contractors. Some say remove it, others say leave it as long as the floor is dry and the old glue is stable. What do you think ?

    Reply
    • Roger

      Hi Denis,

      It needs to be removed, thinset will not bond to it. The easiest way to do that is to let it soak in water for a bit then scrape it off. It is water soluble, so if you leave it, whether it is ‘stable’ or not, and anything happens that gets it wet – your tile is no longer going to be bonded to your substrate. A tile installation is only as stable and durable as what it is installed over. Water soluble glue is not a great substrate. :D

      Reply
      • Denis Blaquiere

        Roger,
        Thanks for the reply. I have been soaking the entire floor, 15′ x 33′, with a hose for the last few days. As long as I keep it wet the glue will “bubble up” and then I am able to scrape it up. Long, tedious process but it works.
        Denis

        Reply
  • Allysn

    I have a 5’x12′ bathroom with OSB subfloor. This bathroom is down to the studs, and about a third of the floor slopes just over half an inch. It seems to run along a joist (turns out this was the builders first house). We’ve had it inspected for structural, termites, rot from water damage, and structurally fine. The room around it we were about to fix when we installed hardwood.

    We would like to install tile in this bathroom, and I read the primer for self leveling cement is not appropriate for OSB. I am not sure how else to level this floor for tile. Do you have suggestions? I am all ears and want to do a good job that will last.

    Thank you.

    Reply
    • Roger

      Hi Allysn,

      I have used primer and slc over quite a few floors without issue, including in one of my own bathrooms. I would go that route. These companies have one thing in mind – covering their ass. If there is even a minute chance that something can happen they’ll just tell you not to do it. Whenever you’re going over wood something can always happen. Your slc will be just fine.

      Reply
  • Yann

    Hi Floorelf,
    Renovating bathroom 96″X84″. Subfloor is 3/4 inch plywood.
    Along the 96″ length the last 20 inches of the subfloor slopes down by varying depths between 1/8″ and 1/32″ along the joist.
    I’m putting 1/2 inch plywood tongue and groove on top as a underlayment, then Ditra heat and porcelain tile. Can I simply ignore the slope or will it compromise my tile install?
    Thanks.

    Reply
    • Roger

      Hi Yann,

      You can ignore a slope that small. What would help is, as you are adding the ditra-heat mat, place a little extra thinset beneath that area and embed it with a straight-edge so it’s flush with the rest of the room. Once the thinset cures that slope will be gone.

      Reply
  • Rob

    Hello Roger I got bathroom and it’s about 12 ft long and it drops3/4 of inch from center to out side. You can’t tell by eye but with leaves you see it. I’m tileing room 12×24 tile. I’m running tile width short side to low side’ I think you won’t see it low as room is flat. What do you think
    Thanks Rob

    Reply
    • Roger

      Hi Rob,

      As long as it’s flat it really won’t be noticed. Just don’t sit your golf balls in the center of the floor and expect them to stay there. :D

      Reply
  • Pam Horner

    I have purchased 8×8″ gauged straight edged quartzite tiles as replacement for cracked porcelain (badly installed) pool bath, entry, and wet bar floors, some are concrete subfloor, some are raised plywood subfloor (not both in any case). The store said I should wash and seal them first. However, if I seal the bottoms and edges, the thin set and grout would be adhering to a thin coat of sealer, instead of the more porous stone, right? Please advise.

    Reply
    • Roger

      Hi Pam,

      Not necessarily. You’re thinking of a sealer as a coating – it isn’t. A penetrating sealer soaks into the pores of the quartz, it doesn’t ‘clog’ them up. Thinset will still bond to the quartzite just fine. You DO want to make sure you use a white thinset if your quartz is lighter in color. Gray thinset, especially when wet, can randomly darken the look of stone from the front.

      Reply
  • Zack Jones

    Hey Roger,

    I’m installing 15″x30″ tiles and I the floor is fur plywood. I am installing a uncoupling membrane down but I was wondering I should use self leveling cement before or after the membrane.
    The floor has dips of about 1/16″ (heavy) in some spots while using an 8ft level.

    Reply
    • Roger

      Hi Zack,

      No need for self leveler with that small of a variation. What you can do is use a long straight-edge while installing your ditra. Spread out your thinset and embed the ditra into it with the straight-edge. Let the thinset cure before walking on it and you’ll have a completely flat substrate. With variation that small the amount of thinset from your trowel while your setting tile will more than make up for it.

      Reply
  • Gene

    Hi Roger,
    I’ve hired a contractor to install 10×40 wood-look porcelain tile in the living area, kitchen, and bathroom. When removing the old tile they cut many shallow, some deep (up to 1″) gouges and pits in the concrete. Now they are applying the tile directly to the pitted concrete and claiming the (mapei) mortar will fill the holes. They said they never use leveler unless it is really really bad. I’ve insisted they use leveler in at least the kitchen which looks like the face of the moon. Today I realized they are using 1/16″ spacers which I’ve read are too small and were sawing the tiles with a handheld round saw, balanced on a bucket instead of on a table. Should I believe them or consider shaking them loose before we proceed further? Thank you so much for your help.

    Reply
    • Gene

      Update: they are saying the reason is to match the level of existing tile which is fair as the existing tile appears to also be directly on the slab.

      Reply
      • Roger

        Hi Gene,

        Many installers have many different methods. While their method may sound unusual, it does not, as far as I can tell, violate any ‘rules’ for an installation. The methods and tools used are relative to where they’ve been trained to install tile. I’ve worked with many foreign-trained (so called ‘third-world’) setters who could cut a tile with all sorts of different hand tools faster than I could with a wet saw. The end result is what you should be concerned with – not so much the journey. :) It may seem unorthodox, but some guys just work like that. As far as the 1/16″ spacers – I use them all the time. Much of the time on tiles that they should not be used on. It has more to do with your skill level.

        Reply
  • DaveB

    Hey Roger,

    I thought I did a great job building up and flattening my floor with plywood and SLU but ended up with some hairline cracks where I really did not want to see them…

    BACKGROUND:
    I did an SLU pour over RPM mats about 3 months ago. It’s a big rambling ranch house and I am running wood-look tile all the way down from mudroom thru the kitchen and down the hallway (@52ft long).

    The home is essentially two rectangles joined together to form a “T” shape. Where those two rectangles meet I had concerns because there was a slight change in height between the two floors (maybe 1/8 -1/4″).

    5/8″ subfloor got an extra layer of 23/32 over it to build it up. Underneath there are doubled 2×10 (4×10) joists 16″oc. When I was bridging the spot where the two rectangles meet (in the hallway) I shaved the underside of the plywood to around 5/8″ to help bridge the height difference . I used adhesive and screws into the joists here because I didn’t want drastic separation of the plywood and subfloor over this bridge point. I normally purposely avoid hitting the joists so this was probably a mistake.

    I glued down the RPM mats with Roberts 2001 and put some staples in the mats to keep them from sliding while glue dried. Laid Nuheat wire, primed and did a continuous pour (TEC SLU) down through whole house. All areas were poured at least to the top of rpm mats. This transition area in the hallway was a bit thicker (@1/2″ thick).

    I had a knee injury and had to leave the job unfinished for last 3 months. I covered the floors with fabric to keep it clean. The area was however walked on quite a bit during this time. Although I feel the floor is structurally sound I’m guessing that walking on the SLU for 3 months stressed the SLU. Because when I went to give the floor a wipe down with water I found 4 hairline cracks running across the floor around this transition area that was bridged with Plywood and RPM\SLU. 3 cracks run about 70-80% across and 1 crack all the way across. See picture attached.

    They are faint hairlines (like a thin pencil line) but you see them better when wet. Tapping across the area with a screwdriver handle doesn’t sound hollow anywhere. They are not crumbling and I feel no movement. Way too thin to get any kind of knife or tool in there. Heating cables are working fine.

    I also have 2 or 3 wandering hairlines in the kitchen area (@ 2-4ft long). Nothing across the whole floor though. For those I mixed a little TEC Multipurpose primer and water and applied to the hairlines letting it bubble down and soak it in till it wouldn’t take any more.

    I’m wondering if I should just put some primer in these 4 hallway hairlines and continue on with tile or if I should maybe Nobleseal TS over the entire floor or at least this hallway\transition area to ensure future cracks don’t transfer up to tile?

    What are your thoughts? I know some hairlines are somewhat normal with wood movement and RPM does hold SLU very tenaciously.

    Have you ever used or seen NoblSeal TS put over radiant SLU before tiling (over other similar membrane)?

    I was already going to add soft grout joints zigzagged across this tile work (in same direction of these hallway cracks actually) so I guess I’ll add an extra soft joint at this hallway hairline area to be safe. I’m also going to add some extra blocking under this these 4 cracks just for extra support.

    Any advice is much appreciated. Thanks!

    Reply
    • Roger

      Hi Dave,

      I don’t see a picture at all on your comment. However, you did state that the slc was thicker at that spot, so it makes sense that you may be seeing shrinkage cracks there. They are nothing to be concerned about. They happen whether it’s been three days or three months. It doesn’t affect anything. I wouldn’t worry about TS over the installation anywhere unless you really feel like you need it, if so it’s completely acceptable to install it in that manner.

      Reply
      • DaveB

        Roger,
        Thank you for that quick reply! I’ve tried attaching those pics again just to show you. I wasn’t looking to do the NobleSeal TS unless you felt these cracks portended future failures done the road. Takin my time to do it right so I don’t have problems down the road.

        Reply
      • DaveB

        Hmm. Uploading various pic formats still not working. Here’s a link to the SLU cracks, plus a picture of the plywood spanning the subfloor joint.

        https://imgur.com/a/t7wyB

        Reply
        • Roger

          Yup, shrinkage cracks. If you notice they begin at a corner on either side of where the slc is thicker, the thicker portions were simply pulling more as it shrunk and it pulled away from the thinner, cured portion a bit. It’s nothing to worry about, I wouldn’t bother with the TS.

          Reply
  • Brian

    Hey,

    So I ripped up my kitchen floor. It appears to have a leveler on the concrete already. My installer said he may have to install a new subfloor to tile over. This seems wrong, can I not just sand the old leveler and place a new one? IF that is even needed ? The floor is perfectly flat already.

    Also, can leveler be cleaned ? In case of mold or any other issues ?

    Thanks.

    Reply
    • Roger

      Hi Brian,

      It depends on the shape the leveler is currently in. It may be sufficient, it may not – I can’t see it from here. :D You can go over leveler with leveler (if it’s in good shape). It cannot, to my knowledge, be cleaned.

      Reply
      • Brian

        Here are a few pictures, if that helps at all.

        So options would be re level or sand down and level ?

        Thanks for your help!

        Reply
        • Roger

          Yes, those are your options unless you want to go directly over it with a membrane such as Schluter Ditra.

          Reply
  • Sarah

    So I have pulled up all of the tile and vct and floating floor in the house and am left with a messy concrete subfloor. I bought tec self leveling underlayment. Its just me working on this so I could only manage one bag at a time. The issue I’m having is where the has met up in some areas there is a very slight height difference. (very very slight) and also some of it is extremely smoothe and in some places a little rough. Before I paint on the vct adhesive, I want to make sure everything is as close to professional as it can be. So I need to smooth these areas where the bags met up or are slight imperfections not noticable when using vct glue and luxury vinyl planks?

    Reply
    • Roger

      Hi Sarah,

      Every imperfection will show through with lvt. Get some feathering floor patch to go over those areas. You mix it up and spread it on with a trowel, you can flush everything out like that.

      Reply
  • Ryan

    Roger,

    SOS… I have a bathroom in remodeling right now it’s 8′ 6″ x 12′. I replaced the subfloor with 3/4″ advantech T&G and then added a second layer of 3/8″ plywood over it. I am using a ditra uncoupling membrane and 36″ x 6″ porcelain tiles. Here’s my problem… I checked my floor (or thought I did) for level before laying the ditra. Tonight i was cleaning up and noticed my level laying on the floor and against one wall the floor is 1/4″ out over about 16″. The rest of the floor is flat and level but up against this wall (8 one of the 8′ 6″ walls) the floor slopes! Is there anyway to correct this now that the Ditra is already set?

    Reply
    • Ryan

      Maybe this is a dumb question… The mortar I’m going to be using to install the tiles is Mapei Uncoupling Membrane Mortar. Since I’m using LFT tiles this is a medium bed mortar. My understanding is that medium bed mortars are made to be applied thicker than a thinset. Could I use the medium bed mortar over the ditra and build it up 1/4″, let if cure then come back over it with my tile?

      Reply
      • Roger

        Sorry, I see the questions in the order they were submitted. :) You can do that as well, but the ditra idea works much better.

        Reply
    • Roger

      Hi Ryan,

      You can fix it, but it depends on how it slopes (you didn’t say). If it slopes UP (that area is higher) just cut the ditra out of that area. It’s small enough that not having ditra under that particular spot won’t make any difference. If it slopes DOWN just cut a strip of ditra and install it over the existing ditra.

      Reply
  • Paul Radvansky

    Hello

    I am building a new walk in shower and created a rubber membrane underneath my concrete base. Then i noticed that the pitch was not good in some spots and I added about 1/8 inch of floor leveler on top concrete. Is this okay or do I have to remove it some way?

    Reply
    • Roger

      Hi Paul,

      It’s fine.

      Reply