Does my Floor have to be Level to Install Tile?

by Roger

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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Hola Elf
Cant describe all the horrible problems on current job, grout joints 1/2″ +, leaks in several places, mold etc.
…A previous contractor??? Replaced part of bath floor and shimmed his 5/8 ply with strips of 5/8 ply, so I am now trying to get back to orig floor that is in other half of bathroom. It has 1 by 6 with 3/4 ply over that. I am going to use HB so I need 1+1/4″ min my question is can I use sm pieces of ply I have on job? I have been adding 2/6 and 2/8 blocks to the joists anywhere that even looks questionable
Also I am installing 16″ tile and the only trowel I could locate is a 5/8 U shape. I sent the homeowner and he looked all over town, so will it work? Thanx Elf, ur a character :lol: :lol:



Hi JayDee,

Yes, you can use the small pieces of ply. Just ensure that you use thinset beneath your backer and it’ll be fine. That trowel is frickin’ huge! Try the internet, I’ve heard you can buy stuff off of it. :D Look for a 3/8″.



Hi Roger,
I’m about to install about 1000 Sq.Ft. 6×24 porcelain tile with a wood look, it’s going in the basement with cement floor. There are expansion cuts all over the cement floor.
1. Do I fill them all, what do I use?
2. I’m planning on using flexbond polymer-modified mortar, is that right?
3. Will I experience crack later on in the tile? How do I prevent the cracking?
4. With this specific tile, what trowel size do you recommend?

Thank you in advance



Hi Alec,

The search box in the upper right corner will lead you to every answer you seek.

1. No, you don’t fill them. You can use a membrane over them to be able to relocate your soft joint, but you don’t fill them, they are there for a reason.
2. Yes, that is one right answer. It’s a good thinset.
3. Not if you properly prepare and install your tile, with soft joints and perimeter joints.
4. Whichever gives you the proper coverage.



Greetings. I have a 30sq ft powder room i will be tiling. I used my 4 ft level to check for flatness, but i have no idea if the surface of the level is flat. Do you have any recommendations on an inexpensive straight edge? Also what is the tolerance for flatness. I have 23/32 osb that will be covered by 11/32 ply, covered by schluter ditra covered by 30cm x 60cm porcelein tile. Great site.



Hi jmd,

I’ve never seen an unflat level. :D Yardsticks are cheap and flat. Your floor needs to be within 1/4″ in ten feet.


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