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.

{ 439 comments… add one }

Leave a Comment

  • Ron

    I want to install self stick vinyal tile over porcelain tile. The porcelain tile is small squares with many grout lines. Should I cover it with thinset or floor leveler. If so. what kind should I use?. Thanks

  • Alan C Sweenor

    I’m redoing my bathroom. roughly 5′ x 12′ the floor is mostly level except about 2-3 ft from the outside wall of the house. roughly 3/4 to 1″. it was two separate bathrooms and now i’m combining into 1. I want to lay porcelain tile but concern about cracking. will be laying it on schluter ditra. If I raise the majority of the floor to match the 2-3 ft area, the transition to the hallway will be roughly 3/4-1″ higher. thoughts?

  • Allen

    Regarding floor flatness with concrete subfloors, I have some questions:

    1. How do you ideally flatten a large area? Especially when you are working alone or with one other helper?
    2. When flattening the subfloor and possibly using something like leveling compound, how do you handle the sawed in control joints? Just cover them up? Fill them with backer rod, foam, or something else?
    3. What’s the easiest way to check floor flatness over a large area?

    Thanks in advance! Also curious if just learning and using the mud set method is better than worrying about getting the floor perfectly flat.

    • Roger

      Hi Allen,

      1. Self-leveling cement
      2. Duct tape over them (really) or fill them with backer rod (cylindrical foam). They are only there to tell the slab where to crack, either method will keep that intact.
      3. Use a laser level and a 5 gallon bucket. Set up your level, shine it horizontally to a spot on your bucket and make a mark. As you move the bucket around the floor the laser mark relative to the mark on the bucket will show you whether it is high or low or level with your initial spot. Ideally you want to make the mark with the bucket sitting at the highest level of your floor, then the other spots will tell you how much lower they are than the initial high spot.

      • Allen

        Thanks Roger! This is good info.

        Any suggestions on a specific self-leveling cement and process to use? Would that be better than more of a dry pack type screed?

        • Roger

          Hi Allen,

          Define ‘better’. :D For me a dry pack screed (mud floor) is the best option 99% of the time. However, most diy’ers who are on my site are not equipped to do anything like that. Slc is the easiest option. In the end, both should give you a flat substrate to work with. Just prime your subfloor, let it cure, then pour the slc following the directions on the bag (they differ).

          • Allen

            Thanks Roger. I will try some of your suggestions. Is screeding out something like NXT Patch a possibility once you get the sides level and flat?

        • Grant collins

          Grid stitch made by Fotress is the only lifetime warranty given to a cracked slab. By using a carbon Kevlar strap running perpendicular to the crack, we can lock in the slab for life. If you do a bandaid fix, future hydrostatic pressure can cause water to permeate those cracks causing more issues. If interested reach out to me.