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 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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