How to Install Absolutely Flat Floor Tile

by Roger

Absolutely flat travertine tile bathroom floorI constantly reiterate the need for a tile installation to be flat. Not necessarily level, but always flat. This is the mark of a true professional and the thing that turns an ‘okay’ installation into a spectacular installation. (Did I just type ‘spectacular? Jesus…) Anyway, the method I use on floor tile to get it flat is fairly simple and ensures that each tile is the exact same height as the tiles surrounding it.

Before I show you that you need to understand, as always, that the substrate preparation is the most important aspect of this. If your tile substrate looks like a skate park you’re never going to get a flat tile installation over the top of it. Your substrate needs to be as flat as you can possibly get it. Take time with your preparation – it makes the rest of the installation run smoothly and gives you a solid foundation.

Start by getting a few tiles set and make sure they are all flat with your straight-edge, just place the straight-edge on top of the set tiles and ensure that there are no open spaces beneath it and that every tile is the same height. You can push down on tiles that may be a bit high or take a tile up and place a little more thinset beneath it to raise it some. Once you have that correct the rest is cake, baby! (You ever seen a cake baby? They’re messy…)

All these photos are of a travertine tile bathroom floor. I used travertine photos because it happens to be one of the least dense stones and usually have quite a few pits and open spaces in the stone itself. If the tile is ‘filled’ travertine, as this is, it is normally only filled from the front so that, once installed, it has no open areas or pits on the face of the tile. You can, however, see these open areas in the back of the tile. I’m gonna show you how to fix this, too. You get a two for one with this post.

Thinset lines all combed consistently

Photo 1

Once you have the initial couple of tiles set, as in photo 1, just comb your thinset onto your substrate in a uniform direction. (Make all the little lines from the trowel go the same way) This eliminates the possibility of trapping air beneath your tile and leaving spots that are not fully adhered (hollow spots). If you make the pretty little swirlies they may look cool, but they can also trap air beneath your tile. On a side note: my spell-check just told me that ‘swirlies’ isn’t a word – so I’m makin’ it one.

In photo 2 you can see the back of the travertine tile. See how it has all those pits and crevices and empty spots? You’ll want to fill those up with thinset to give the tile a good, solid fill and, essentially, make it more dense and durable. Do this by using the flat side of your trowel (Photo 3) and scraping thinset along the back of the tile in every direction. This ensures it is completely full and there are no open areas left. (Photo 4)

Back of travertine tile - unfilled

Photo 2

Backbuttering travertine tile - filling all the spaces

Photo 3

Backbuttered travertine tile - completely filled

Photo 4

-This is what is called ‘backbuttering’ your tile. You’ll more than likely run into that term a lot when researching tile – that’s all it is. For an installation where you have an inconsistent tile or a questionable substrate you can always do this, then flip your trowel around and comb thinset on the tile as well (make pretty little lines – not swirlies!)

Now that you have a good solid piece of shiny rock to put down on your floor, flip it over and put it there. Make sure you flip it over – shiny side up. :D When you place it in the thinset on the floor place it directly against the two tiles adjacent to it (Photo 5) so that two sides of the tile are actually touching the two tiles next to it. As you do this you can push the tile down to just the right height to be flush with the tiles next to it.

Placing tile directly against adjacent tiles

Photo 5

This will ensure that the tile you just put down is the same height as the surrounding tiles. You can take your straight-edge again and use it to push the tile down and get it to the same height. If your tile goes down too far – PULL IT UP! and put a little bit more thinset beneath it.

I yelled ‘PULL IT UP’ because for some reason people think that once the tile is down – that’s it. It can’t be moved. That’s not it. Until the thinset cures – tomorrow! – that tile can be moved, pulled up, adjusted, smashed, replaced, etc. Do not be afraid to pull it back up and put more thinset beneath it if it sets too low.

Pulling back to get total coverage

Photo 6

After you get the tile at the proper height, and this needs to be along both edges that are touching, then you can go ahead and pull it away from the two tiles to create your grout line and make sure you are, indeed, at the proper height. (Photo 6)

Then just insert your spacers and make sure it is in the correct place. (Photo 7) Pulling it back also ensures that there is full coverage between the thinset and the back of your tile. Remember those little ridges that the trowel created? The ones that were not fully squished down as you were adjusting your tile will be pulled slightly as you create your grout line and this will create full coverage and support beneath your tile.

Insert spacers and you have an absolutely flat floor

Photo 7

Check with a straight edge - told you, absolutely flat

Photo 8

-You can take your straight-edge and lay it across the tile to ensure that they are all perfectly flat. (Photo 8 ) If one sets a little bit high you can simply wiggle the straight-edge back and forth until it is flush. If it sets a little too low – PULL IT UP! (damnit) and do it again.

It may seem like a tedious process – it is. But when done correctly you end up with a totally flat, professional looking tile installation which will last for years.

See: 8)Absolutely flat travertine bathroom floor tile

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I have a small bathroom in the basement I am attempting to tile using Ditra.
I understand what you say about flat not equal to level. That being said, the
Ditra is not uniformly flat – I attribute that to the concrete that the plumber used to relocate the drains for the toilet and the shower and my attempt to lay the Ditra without lawn roller :-}. Query, should I remove the Ditra and start over or give a try anyway and hope that lippage will be minimal ? Thx in advance.



Hi Roger,

My GC tiled our shower floor with 2″ mosaic tiles and they are not flat. Seems like common sense to level the tiles with a straight edge but when I asked how he installed the tiles, he told me he used his hands. Is using a straight edge a basic tiling concept that all GC’s should do? Are there any tiling standards (we live in Fremont, California)? He wants me to pay more money for demo of the uneven tile and re-installation. I think he was careless and he should take responsibility. Please share your thoughts.

Thanks in advance,



Hi Will,

It is standard procedure to get flat tile. How one goes about that varies wildly. I can get flat tile with just my hands, but that’s experience and it’s more difficult. If it is not flat it is a poor installation. Unfortunately there really are no ‘codes’ that must be followed unless it is done specifically through your local building department. You’d need to contact them to find out what constitutes an unacceptable installation.


Amy Lioson

Hi Roger,

I am so glad I just found your site, thank you for all the useful information.

I have pulled the carpet out of our family room, I cant tell you yet whats underneath the plywood (if thats plywood, it looks like little strips of wood) i.e. joist distance etc, I cant recall the proper terms you used, but I can tell you for sure that the contractor used materials build to minimum code only, nothing extra.

I have wood floors right beside it and I want to install porcelain flooring in the family room so I need to have the porcelain at the same height as the hard wood floor. After reading your web site, I am coming to the conclusion that I simply cannot use backerboard unless I am Ok with a height difference which I am not, so all of this to ask about Ditra, I understand from what I have been told that I can use a Ditra membrane and this will ensure that my tiles will not crack and that by using Ditra I dont have to worry about the subfloor does this sound correct? Its a very expensive product so I want to be 100 percent sure that it works

Your advise is greatly apreciated.

Thank you


L Pollution



Hi Amy,

It does work as intended. However, you still need a proper subfloor beneath it, which would constitute 1 1/4″ (3.2cm) thick double layer of plywood beneath it, with the proper framing. If it is minimum it has the proper framing, but likely doesn’t have the double layer. It will minimize the height difference for you.



I have a room / bar, 11 x 19, with 3/4 T&G subfloor over 2 x 8, 16 on center joists, suspended but every 4 feet or so there is a half inch redwood wedge against the slab. I’m about to install thinset, Ditra Heat, thinset and 4 x 32 travertine plank. I’d love to install with no grout line, but my friend says I have to have a 16th at least. At the tile store party, a guy gave me a package of his new diamond leveling spacers, a little circle with cross inside and wedges, and flat squares with toothpick like handles to pull up on. He was demonstrating it. I’m going to use our best outdoor patio mason, his helper and myself to do the job. What about the spacing and cracking? Cyn



What about it? :D

You NEED grout lines, period. I don’t understand what a half inch of redwood wedged against the slab is? Properly built you will have no cracking, what cracking are you referring to?



Our contractor just tore out 50-year old tile in our bathroom and replaced it with larger, 12×18 (approx.) tiles. It is not level by 1/8-1/4″ of an inch. It is flat, though. Big deal or or major impact?



Hi Suz,

It’s done correctly. As long as it’s flat that is sometimes all you can do. For instance, if the floor at the doorway were 1/4″ lower than the back of the room, leveling it will require raising the floor another 1/4″ at the door, causing problems with the transition into the next room. As long as it is flat it is correct.




I just had my master bath tiled with 18×18 tiles. There was a heating element installed with a thin-set mortar before the tile was added. The tiles are not flush in many parts of the bathroom and I am wondering if this is to be expected or not. Thank you.




Hi Alicia,

Absolutely NOT! It sounds like you had a contractor who had no idea how to correctly install tile over heating. It is not proper, and it needs to be redone. Your floor tile should be absolutely flat, no matter what you have beneath it.




I am getting ready to lay down marble hexagon tiles, a bunch attached to a mesh. During subfloor prep I encapsulated radiant heating into Self Leveling cement. Unfortunately the concrete is not flat. Do I need to pour more to flatten it, or can I fill the gaps with thinset and level it using your approach here.




Hi Yev,

You can use this technique with mosaics, but it’s a huge pain in the ass (you’ll have thinset squirting through the grout lines). I would level it out with slc or thinset to get it flat first, it’ll be MUCH easier.



Good day,
We had a honed travertine floor installed using a schluter system in the bathroom and there are areas where stones meet but they are not level to each other. The worst areas are maybe a couple finger nails thick where the butt up to each other. The GC says that is the beauty of stone, I think they took a short cut. We paid well for the job. When there is unevenness like this can they sand/grind to smooth the variance going from a low to high grit? If so would this be part of a normal installation? Might we be more disappointed after this type of fix?
Thanks, Steve



Hi Steve,

With a honed travertine the tile should be flat and flush with one another. It’s called lippage, and while there’s an acceptable amount, it’s normally less than the height of a dime. It can be sanded down and finished but to get a professional job on it you need to hire a professional to do it. If not done correctly it will definitely look worse than it currently does.




I am tiling my floor with 13 in square tiles. I applied 1/4 in hardibacker over a wood subfloor per your instructions, taped and all. I was checking out the level of the floor and I noticed that when I “dry laid” out my tiles over the floor, there were a few tiles which are “rocking”, creating about 1/4 in “lippage” if I make one side of the tile perfect with an adjacent tile and then measure the height difference on the opposite tile.

I think that the root cause may be that I applied a small amount of extra thinset over the seams. (Although, the build up is only about 1/16 of an inch on the seams.) Anothe possibility is that I also had replaced a plywood sheet in this area before installing the haridbacker and it was not exactly the same thickness as the extsting ply (but off by a very small amount, like 1/32 of an inch).

My question is whether or not the tiling technique that you recommend can compensate for this 1/4 in of potential lippage. Or should I resort to something more dramatic like a self leveling cement.



Hi Jim,

I just answered your question where you asked it the first time. :D Yes, you can make up for that with this technique.



First of all, excellent advice on this site! A couple questions for a major tiling job I’m embarking on. We purchased a foreclosure which has 24×24 honed and filled travertine in the living room. Several tiles are cracked (I suspect because installer did not put cement board over the plywood substrate before tiling) and we are going to dig them out & replace them. This size is very difficult to find and may end up going to Miami to ferret some out. We want to tile the bedrooms in 18×18 travertine and want to do it right. I’ve read a 1/2 cement board is appropriate over the plywood floors in the bedroom but what if the height of the backer board and 1/2 travertine creates a lip between the new tile and old at the transition point? How to handle? Can I use 1/4 backer board or is 1/2 the way to go?



Hi Dawn,

Transitions always need to be made. NEVER compromise a tile installation because of a transition. You can use 1/4″ backer on a floor provided you have thinset under it (as well as under 1/2″, should you choose that). However, the floor substrate itself requires a double layer of plywood above the joists with a minimum thickness of 1 1/8″. You can not go over a single layer with backer and not get cracking. Your cracking problem is likely either no second layer of ply, no backer, or, if he installed backer, I can nearly guarantee that there is no thinset beneath it.


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