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

If you would like to receive little bite-sized pieces of my wealth of useless tile wisdom sign up for TileTips. You will receive a short (it’s short – I hate long emails) little email with tips, tricks and secrets (and bad humor) all wrapped up in one shiny little package. You will get one or two a week (depending on my drinking schedule) and they will help you set tile like a pro. Or, if you’re a pro, they’ll make your job sooooooo much easier – and make you rich and famous. 8)

Previous post:

Next post:


Hi Roger, can I tape over partially ground fiber mesh tape for floor joints. Put down self adhesive tape and covered with thin set. Smoothed it out and let it dry and guess what? Yes. Little speed bumps all over the floor.
Sanded down the bumps that led me to find other imperfections as well.
Did I read that you tape as you go instead of tape and let dry?

Thanks in advance


Rob R


This is a great site, there is so much useful information. Thank you.

We have had 2″ marble hexagon tiles installed on our master bath floor. At this point, the contractor has completed the tile work. There are 2 things I notice when I walk on the floor:
1) The floor it is NOT flat. I can feel the slight ups and downs under my feet. This seems more apparent in the middle of the floor. Around the edges – it seems reasonably “flat” at least as far as my feet can tell.
2) The individual 2″ hexagon’s differ in thickness and I can see and feel these differences.

My contractor is telling me that he will do a “polishing” which will smooth out the edges. I can see how this may go to address #2 above, but I don’t think it will address #1.
My question to you is:
1) Will polishing address the non-flat floor (#1 above)?
2) Is this non-flat (uneven) flooring something that is very common to small tile (i.e., 2″ hexagon marble) floors and the uneveness is just inherent in these types of floors?
3) Or is there a way to ensure a flat floor even with 2″ tile?
Thank you,



Hi Rob,

1. ‘Polishing’ – no. If that’s actually what he means. It can be ground and polished, which would solve the issue with #2.
2. It is an issue inherent to the specific mosaic. They SHOULD all be a uniform thickness, but not all mosaics are created equal.
3. Yes, begin with a flat substrate and use guaged stone mosaics (uniform thickness).


Sonja Tanguay

I had rectified porcelain 6″ and 8″ W by 48″ L wood look planks installed with a 1/16″ grout line. We used Mapei Flexcolor CQ grout but it looks low and is not flush with the tile. Can I add more grout? What can I do?



Hi Sonja,

Yes, you can add more grout with the CQ.



Awesome info!!

Can you tell me what method can be used to clean up the grout, so that it stays filled to the edge of the flat tile? Using a sponge removes too much and leaves the sharp 90degree edges of flat tile exposed in places…



Hi Alexis,

Squeeze absolutely every drop of water you can out of the sponge then go over the grout line very lightly, without pushing the sponge down, which digs grout out of the line. You’ll need to do it several times to get clean tile and a full line.



You mention back-buttering tiles; I bought 12×12 PEI 4 Porcelain tiles from Lowes (made in China of course), and they all have wavy groves on the back (about a 1/16″ deep). Does this mean that I have to back-butter every one of these times, before setting in the thinset?

Next, unrelated question. Can you provide me instructions, or a reference, for creating a ‘divot-drain’ (using a standard clamp drain), when using Aqua-defense as my topical membrane?

Many thanks Roger; I recommend your site to many people!



Hi Daniel,

Yes, skimming the back of the tiles with the flat side of the trowel to fill those grooves is the only way to get proper coverage. My buddy Jim has a great video on the divot drain.


Bob O

Love your easy going advice. Love your humor. Your the best. Will you be my best friend? I’m a carpenter by trade if you have any framing questions.
Bob O



Hi BobbO (Can I call you BobbO?),

I would be an absolutely horrible best friend. I drink a lot, tend to hide out in my garage building my car, yell at everybody when things go wrong, throw shit – A LOT, and am generally just a miserable son-of-a-bitch. I also LOVE practical jokes – which means you would never be able to simply drink a beer around me – I’m always gonna fuck with your beer. It’s just who I am.

Humor has a price. :D




Love this site. Have gotten much information on DIY.

I’ve got my final deck on the shower floor but realized I did not do a great job getting the deck mud absolutely flat. It’s pretty close and the pitch seems right, but there are high and low spots and test setting the tiles shows that it is not optimal. I will likely end up with corners either sticking up or too low. Can I screed in a layer of thinset to level it before using thinset to set the tiles? Want to get it as close to even as possible.

Thanks, Frank



Hi Frank,

Yes you can.


Joe P

Howdy, Roger. How do you feel about tile leveling systems. Specifically the cheap one from Home Depot (QEP) that uses wedges to keep two tiles at the same height. I want to use these to make leveling easier but at the same time I’m wondering if it will put too much stress on 18″ travertine.



Hi Joe,

I regularly use the MLT system. The lash works fine, but it’ll kill your thumbs by the time you’re finished. :D It won’t put too much stress on the travertine. You need to have them almost perfectly flush with one another before inserting the wedge. Just think about it as a system to hold it in place as the thinset cures (preventing the shrinking thinset from sucking one of the tiles down) rather than a tool to make it level. It’s more the former than the latter. You still need to get them very close, any system will not replace the skill, it simply locks the tiles together while the thinset cures. It will assist in getting them completely flush, though.


Russ Stangl

Greetings Roger: My Masterbath floor project will include 30″x30″ porceline tile. The initial sub-floor (5/8″) will be supplemented with 5/8″ T&G fir plywood including an appropriate expansion space of 1/8″. Do the plywood seams need to be treated similar to the tile board seams? Modified thinset, 1/8″ or 5/16″ Ditra, unmodified thinset and finally the tiles will be the sequence to the completion of the job. As a novice to this type of process I am researching the use of a tile levelling system because of the size of the tiles. Welcoming your comments, I am……….Russ



Hi Russ,

No, the plywood seams do not get treated. If the room is more than about 150 square feet I would fill the seams with silicone or caulk so they don’t get thinset in them, allowing for expansion. I regularly use the mlt system, love it.


Russ Stangl

Hello Roger: Appreciated your initial response. Additionaly, is one required to put a foam like material around the perimeter of the room ( I assume for expansion purposes )? As well as putting down 30″x30″ tile on the floor, I will be putting 36″x12″ porcelain tiles on some of the walls in this master bathroom with 9′ ceilings. The walls are of 1/2″ drywall sheets; in one section of the wall at the vanity there is 5/8″ plywood. Do I need to enhance the walls in any way before tile installation? Are there any technical procedures for this operation of which I need to be aware? Thanks for the wisdom.



Around the perimeter of the room you need a perimeter joint. It doesn’t need to have foam or anything else in it (you can if you want, but no real reason to), it just needs to be a 1/8″ – 1/4″ open space between the tile and baseplate or wall for expansion purposes. It gets covered with the baseboards.

You can install tile directly to the drywall, but the plywood needs to be replaced with either backerboard or drywall – some sort of more stable material. Plywood expands and contracts way too much to have tile bonded to it last for any significant amount of time.


Leave a Comment

;) :wtf: :wink: :whistle: :twisted: :suspect: :shades: :roll: :rockon: :oops: :lol: :lol2: :lol1: :idea: :guedo: :evilb: :evil: :eek: :dance: :cry: :corn: :cool: :censored: :bonk: :arrow: :D :?: :-| :-o :-P :-D :-? :) :( :!: 8)