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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  • Henry

    Hi there,

    I’m struggling to decide if I should pour concrete to level off my basement floor as there is Drainage in the middle of the washroom which is a bit higher than the rest of the floor. If I was to pour concrete and level it, it will raise the floor height where my door is and then of course I would have to level the rest of my basement. Is it possible to lay the tiles with a extra martor to level with the drain and then gradually lay the tiles to the level of the floor at the door? The height difference is approximately 1/4 – 1/2 inch at the highest. There is also a toilet flange behind the shower wall that I am concerned about if I was to level the floor. The top of the flange is perfectly leveled with the drain height.

    Thanks in advance

    • Roger

      Hi Henry,

      Most mortars are only good up to 1/4″ thickness or so. They are not made to level or flush a floor, that needs to be done prior to installing tile. You can use a floor patch, which will allow you to go from the drain height down to flush at the doorway. If you use slc you’ll need to do the entire basement.

      • Henry

        Thanks Roger! I will try it out.

  • David P

    Hi Roger,

    My question is this: do i need to cut up what I did and reinforce the subfloor better or can I use what I’ve done?

    I am installing a 72″x42″ shower with a 20″ bench in my upstairs bathroom, my house is older (1929) and the floor joists are 24″ apart on centre, with 3″x1″ tongue and groove boards covering the floor. There is an area of about 18″x24″ missing at the back corner around where I had to modify the plumbing. Being as old as the house is, the floor is not level so I placed over the shower area a layer of 3/4″ construction grade plywood. primed it with levelquik, stapled in the metal lath (I did not overlap the joint but butted it up and stapled across it), and poured the levelquik rs. I mixed half the bag the first time, poured it, realized it wasn’t enough, mixed the rest of the bag poured it (I used the proper amounts of water). still didn’t cover the 52″x42″ area that will be the shower pan. So i let it set overnight, re-primed the surface as it had sat for long than 12 hours and poured another bag on. That had it level. no one touched it for over 8 hours, it was great for the last 3 days but today it has 3 long full depth hairline cracks running out from the drain hole to the edges of the pan area. I am worried the cracks are due to lack of support in the subfloor and too much deflection.

    I am willing to cut that section of floor out, throw it away (cries a little), and build a stronger and level support. But if this is some issue with self-leveling cement, and it would be fine if I didn’t I would rather not.

    I am going to be using the schluter-kerdi shower system to waterproof with a 48×48 preformed pan cut to the right size and filled out with dry pack mortar (I am using sacrete sand mix and play sand) and I bought Mapei Kerabond for the thinset. I really don’t want all this hard work and expensive products to go to waste if I need to remove it all to reinforce the floor because my shower tiles are cracking.


    Thanks, your blog is a god send.


    • Roger

      Hi Dave,

      It’s actually just fine. Those hairline cracks are shrinkage cracks from the multiple pours. It’s not going to affect anything at all.

      Get to work! :D

      • Dave Pivato

        Awesome! Thanks!

  • Heather


    Question regarding Re& RE of my acrylic shower base. Contractor replaced shower base had to take one row of tile off to complete(tile is 12 x 24). Have now reinstalled new acrylic base and installed tiles, I now have a space between the base and my tile ranging from 1/8 to 7/16 all the way around that was grouted and the grout continuously cracking. Contractor says this is normal and there is nothing wrong with install and he assures me the base is the same size. I don’t know if they didn’t level the base or if the base is not flat or is a different size. The tiles are all the same size so it’s not the tile.
    Is it normal to have a uneven grout line of this size? How do I prove base is not flat? Should it be grouted between tile and base or silicone?
    Thanks for your help.

    • Roger

      Hi Heather,

      It should be silicone between tile and acrylic – always. Put a level on the base to see if it’s level. No, that is not normal.

  • Brady Porter

    I am installing porcelain tile over a plywood floor with 1/2 Hardiebacker on top. When we installed the Hardiebacker we taped and mortared the seems leaving a small hump at almost every seem. I am not sure how big the humps are, but I believe they are smaller than 1/8″. The tile we are using is 12×24 and it rocks a bit on the seems. Would you recommend adding SLC on top of the hardiebacker, or will the mortar bed be able to make up the difference and prevent too much slippage?

    • Roger

      Hi Brady,

      Provided you are using a correctly sized trowel (3/8″ or larger) those little humps won’t make any difference at all.

  • DeAnna

    When jack hammering our old kitchen tile, lots of holes were created and yet it left so much mortar. We have tried everything to remove the old mortar but it is as if the old tile was installed with cement. Can I just fill the holes with new mortar and hope I can get it flat enough as I lay the new 1 ft by 2 ft marble tiles?

    • Roger

      Hi Deanna,

      Holes in what? What is the substrate you plan on laying tile over? You can use thinset to compensate to an extent, but if you don’t have a proper substrate, especially for marble, you’re going to have issues with the installation.

  • Craig


    I’m doing a kitchen remodel and laying 6 x 24 Porcelain tile that will run through the kitchen and adjoining dining room. The issue is the kitchen has an old lineoum floor that has asbestos in it, so I decided for now to leave and install my new tile over it using SLC to any low spots so its flat, then 1/2″ thinset, 1/2″ backerboard, 1/4″ thinset and the above tile. The adjoining dining room is about 1/8″ lower than kitchen floor, so I had planned on using Slc to bring the dining room up to be flat with the old lineoum floor in the kitchen and then continuing the same plan as listed for the kitchen. I have read in one of your posts that I should in the dining room, just attached the backerboard, then the slc, not the way that I had planned to keep everything consistent, I’m open to suggestions or corrections on making these two rooms look great. I was just concerned how I would make sure both floors are the same level doing them in a different manner and end up with a lot of lippage between the two rooms.

    • Roger

      Hi Craig,

      Put down the backer first. The reason is simple, when you screw through a poured concrete product it breaks it apart and compromises it – slc is a concrete product. Once you get your backer down and pour slc over the entire area you will have a flat level floor – that’s the purpose of slc, that’s what it does. :D Doesn’t matter which order you put those products in to get it flush. If you use slc last there will be no lippage between the rooms.

  • Craig


    I may have a severe transition between a dining room with new tile installed about 3/4″ above, the carpet living room. Besides using some form of a reducer for the transition, what have you used that is more gradual or other suggestion?


    • Roger

      Hi Craig,

      I have ramped the carpet up a bit to meet the tile at a less severe angle, but there really isn’t much you can do with that short of a reducing transition.

  • Janene

    I’m running into an issue with our kitchen/dining room floor. I live in a 100 yr old home and my floors are very uneven peaks and valleys aren’t the words for my floor. Right now I have linoleum with subflooring down that needs to be replaced. What is the best flooring with the best cost to put down? Is it possible to put ceramic tile down?

    • Roger

      Hi Janene,

      Yes, it is possible. But you’ll need to flatten the floor first, the best way to do that with a highly uneven floor, which it seems yours is, is to use a self-leveling cement (slc).

  • Roxanne

    Hi. My home is about 60 years old. And I had porcelain tile installed in the kitchen. Soon after the installation I noticed the grout was cracking as well as crumbling in some areas. The installer attempted to rectify the situation. It seemed okay and then a few weeks later same issue. The tile was installed over plywood and had a area that was a little higher almost if it was a mound which he said he would fix. I am not sure what the issue was. The mound is not noticeable to the eye but if you place a water bottle in that area it seems to roll downhill. So, my question is do I need to have someone come in a reinstall the tile flooring or can the grout be repaired and not worry about the leveling of the floor. I really don’t know what to do. It was almost $2000 for labor and materials. Help!

    • Roger

      Hi Roxanne,

      Your floor should be flat. It doesn’t necessarily need to be level, but flat is imperative. If it is not then you have an incorrect installation. If your grout is cracking, and he really did install it directly to plywood (???) you REALLY have an incorrect installation. So yes, unfortunately it likely needs to be replaced by someone who knows how to do it correctly.

  • Kelsey


    We have some old tiles down on the floor that were under some lino we have just pulled up. We wanted to put some leveler down and fit new tiles. Do we need to remove all the old tiles first?


    • Roger

      Hi Kelsey,

      That would be the best option as you don’t know what is beneath the current tile nor how it was installed. It may not be stable or durable enough for a tile installation over it.

  • Tim

    I have officially gotten all ceramic tile and mortar up from the concrete slab. Still trowel marks showing but it’s smooth. We good to lay tile?

    • Roger

      Hi Tim,

      Yes, you should be.

      • Tim

        Cool, thanks.

  • Barbara

    Hi there,

    After pouring new cement to level our concrete basement floor, our contractor installed ditra this week. Last night while looking things over with my husband, we noticed peaks and valleys in a number of areas (ie measured in decimetres). After speaking about the issue with the contractor, he says he can fix the problem by adding extra thinset in the valleys on top of the ditra. Does this sound like a reasonable solution or are we better off firing the guy and starting over?

    Thanks for your advice.

    • Roger

      Hi Barbara,

      In decimeters? Really? That would translate to more than 3 inches, or 75mm, to me (but I’m just a dumb American…). If it is in fact that large of a variance then hell yes, fire him. Or give me a number in mm and I can let you know. :)

      If the variance is less than 10mm or so then yes, he can reasonably make up for that with thinset beneath the tile.

      • Dennis

        You said cannot very more than 10 mm is that over the entire floor or per foot

        • Roger

          Standards dictate no more than 1/4″ (6.5mm) in ten feet (3m) and not more than 1/8″ (3.25mm) in any one foot (30.5cm).

  • Jack

    Hey Roger,
    I don’t know how often you reply or when you’ll see this but I’m in a bit of an emergency and a time restraint. I’ve been spending the past year and remodeling the kitchen myself everything’s going great, except for the hiccups that always occur in remodeling. When I got to the kitchen floor, after removing the tile and backer board or cement backer board we had to replace one and a half of the subfloor plywood sheets. Upon taking them out I decided to fix the floor a bit and sister Joist some joists. Put in some blocking and a few other things to make the floor stronger. Before removing the wood several friends of mine have noticed that there is a little slope in the floor… which brings me to my question. This was the first for him and hundreds that I’ve been through where I found someone that said it doesn’t really have to be level but only flat. I’m glad to hear this. Because of finding this situation in my floor it is put me behind several weeks. So, I wanted to ask you I have remove tile and backer board and the tile that was originally there seem to be OK with no problem except a few pieces of tile around the edges that I’ve become loose because of no threshold. I’ll have to say that this floor I’m on other things in the house we purchased was not done properly but the floor seem to stay together pretty well. I’ve decided to remodel and make the kitchen look better stronger and I will be having an island and countertop with quarts and granite and a stove that weighs nearly 600 pounds in the island. So I needed to beef up the floor a bit before I put down the tiles. Is it common to have an unlevel floor but still have the tile be OK? I just want this to be over so I can get my cabinets in. It’s a small 11.5 x 11.5′ kitchen but I took down one wall and opened it up into the dining area. So should I just put down The subfloor plywood that needs to be replaced glue and screw it in and put a thin set in there and with backer board and then another thin set in there with tile and be done with it? I guess I could always put more thin set down in certain areas to make sure that there is no lippage..I just tried to do my best to make sure that everything is flat when I’m putting down the tile. Anyway I don’t know if this makes sense but any help at all would be gratefully appreciated.

    • Roger

      Hi Jack,

      Provided you install your tile properly you will have no problem with it at all.

  • Devin


    I am placing 18″ Travertine tiles on the floor of an 8′ X 8′ bathroom in my 1920s house. The floor joists are 2X10s on 16″ centers with about 10 feet between supports. The current subfloor is 3/4″ shiplap (plank) installed on diagonals that run continuous under the walls between rooms. The floor also slopes 1/4 to 1/2 inch toward one end.

    I am considering some additional support to the joists because they’ve been modified for plubming but my biggest question is about the subfloor. I’ve read that adding 1/2 inch plywood to the shiplap would be a good idea, screwed to the shiplap NOT the joists. Then I was thinking of pouring self leveling compound, installing DITRA over that, then the tiles.

    My biggest concern is that the surface of the shiplap is uneven in places so there will be a lot of little areas where the 1/2″ plywood is not continuously supported. With all of the steps to minimize deflection that seems like it could be a problem. What would you suggest?

    • Roger

      Hi Devin,

      Exactly as you described, except I would place a layer of thinset beneath the plywood and shiplap first, then lay the plywood in it. That way once it cures your ply is completely supported.

      • Devin

        Thanks much Roger! Do I place the plywood in the thinset while it’s wet and screw it down right away or wait for it to dry as you described below? And I assume I can do this with just a straight edge trowel?

        • Roger

          I would use about a 1/4″ v-notch or square notch trowel, You want the ridges to be able to touch both boards in areas that aren’t flat. The thinset makes up for that. You can screw it down right away.

  • Jes

    What is the best method to obtain a flat plywood underlayment for ditra XL? Subfloor is 5/8″ with high and low spots 3/8 -1/2″ max, joist 12″ oc. SLC to fill up the low spots followed by 1/2″ plywood? I’m concern of screws cracking the SLC. Will this create a problem? I like to glue some “furring strip” cutout matching profiles of the low spots for the screw and use SLC around the furring strips beneath the 1/2 ” plywood? thanks for your help

    • Roger

      Hi Jes,

      The easiest way is to install thinset beneath your plywood or backer substrate, lay the substrate into the wet thinset and get it flat, let the thinset cure then screw it down. The screws will crack the thinset around the penetration, but that won’t make a difference, it’ll only be around the penetration. The slc, on the other hand, is a monolithic pour, meaning that once it cracks the entire pour is compromised if it’s cracked.

  • Arthur

    I replaced a small portion of my wood subfloor in my kitchen, now the piece I replaced is about a 32nd of an inches higher on a portion of the seam. will it make a difference if I lay the vct tile over it.

    • Roger

      Hi Arthur,

      Yes it will. You need an ABSOLUTELY flat substrate with vct.

  • Ken

    How flat is flat enough. I have a large room – 12×24 and I have a concrete slab floor. Took off the carpet. What kind of variance over what length can be tolerated when using tile (36×6 faux wood porcelain) and or engineered hardwood (haven’t decided which I am going to use)

    • Roger

      Hi Ken,

      Allowable variance is 1/4″ in ten feet and no more than 1/8″ in any two foot span.

  • Orlando Solorio

    Hey Roger question. I am tiling on a concrete sub floor but there is a lot of glue from what I believe was hardwood flooring or laminate. I have attached an image. So question is do I have to scrape all that glue off? Or can I just install over it.

    • Roger

      Hi Orlando,

      You want to get as much as humanly possible off of there. You can scrape (try soaking it in water first, makes it easier) or grind it off, if need be. Thinset will NOT bond to that, so you want your slab as clean as possible.

  • Ana

    Hi Roger. I am wanting to have tile that looks like wood installed over my existing tile and carry it over into the bedroom. However the bedroom has always had carpet therefore there is about 1/2″ transition. Can you tell me if this can be done and how? Thank you.

    • Roger

      Hi Ana,

      You can install 1/2″ durock in the bedroom everywhere the carpet is. Or, better yet, remove the existing tile. :D

  • Jared Duplantis

    Hi, I’m wanting to lay ceramic tile from my kitchen into my living room however. The cement slab where the kitchen and living room meet are different hieghts. About 3/8″ to 1/2″ difference. The living room was an add on so the slab wasn’t poured at the same time. What can I do? Also, considering staining the living room maybe. Thanks :censored:

  • Nate

    I have a bathroom floor in a basement we are finishing. The floor concrete and we have poured self-leveler over it to deal with a small peak at a seam. Can I tile directly over the self leveler, or do I need to put something like DITRA down over the self-leveler first? (The room is 5×7)

    • Roger

      Hi Nate,

      You can tile directly to the slc.

  • Rick

    What is the best method to obtain a flat subfloor. The subfloor is 5/8″ plywood and there are a couple low spots, about 1/8″ to 1/4″ max. I believe the knuckleheads who built the house put a couple joists crown down. Shingles and roof felt followed by 3/8″ plywood followed by 1/4″ durock; or 3/8″ plywood followed by 1/4″ durock and then the low spots filled in with SLC? Thanks for your help.

    • Roger

      Hi Rick,

      No shingles or roofing felt. The ply, durock with slc over it (thinset beneath the durock) will work just fine.

  • Kathleen A Ferraro

    The contractor who replaced the tile in our bathroom after it was damaged by water and chemicals used to put out a fire wrote in his insurance proposal that they would remove and replace 1/2 inch cement board and 3/4 inch BC plywood. The bathroom had been installed in 2002, and we had had no problems with the tile or grout until the fire. The height difference between the tile floor and the wood floor in the bedroom was less than 1/4 inch. We indicated we wanted it to be restored to its pre-fire condition.

    The new floor is about an inch higher than the original one. The contractor cut the bottom of the door to fit. The door is now 3/4 inch shorter and there is barely 1/4 inch between the bottom of the door and the floor. In addition the floor feels kind of lumpy underfoot. I am also concerned that the height difference might create problems with our curbless shower.

    The wall tile job is also terrible. I have not paid the contractor’s final payment and don’t plan to. My guess is the contractor did not replace the old cement board and plywood before installing the new floor, but could something else have caused the height difference? I can send photos.

    • Roger

      Hi Kathleen,

      I think you’re probably correct. That’s a huge height difference. He likely just went right over what was already there.

      • Kathleen A Ferraro

        Thanks, Roger. A floor inspector came today and was able to look below the new plywood and found it had been installed over the old subfloor. The contract says remove and replace subfloor, so I believe this is a breach. The inspector also said the floor is moving and has bumps in it. I am waiting for his report on the floor and the wall tile and plan to send the contractor a letter saying I will not pay until he fixes the problems with the floor and also the poor workmanship with the wall.

  • angel barros

    Hi, First I want to congratulate you for keeping this page, it helps a lot to installers like me.
    I have a project of 4500 sf on a second floor. the substrate its a lightweight concrete over wood beams, and needs a lot of prep. i’m planing on patching cracks and then self leveling the floor and install a ditra underlayment and then lay tile with 12″x24″
    My questions is, if the lightweight concrete its going to support the weigh of the tile, I’m worrying about doing a good installation that can fails in a year with a bunch o crack tiles or worst.

    • Roger

      Hi Angel,

      If you are talking about gypcrete – yes, it’ll support it just fine. Be sure to use the primer for the slc to ensure a proper bond to the gypcrete.

  • Albert

    I live on the second floor in a condominium. I am replacing the marble tiles with 24″X24″ rectified polished Porcelain tiles. The existing area has plywood sub floor with 3/4” concrete over. I am tiling the foyer, kitchen and the powder room. The floor slopes down from the entry door toward the kitchen of about 1”. I am confused of how to tile the area with the existing condition. Does my floor have to be level to install tile? Some installers have suggested to remove the concrete and use Hardie Backboard for tiling. Others have different way of leveling the area which is to use paper on plywood, pour cement mortar and thinset and then tiles. I am really confused. What is the correct way of handling this project? I appreciate your help?

    • Roger

      Hi Albert,

      The best solution is self-leveling cement. I highly doubt it’s actual concrete, it’s likely gypcrete (lightweight concrete). Your floor does not need to be level, but it does need to be flat.