I 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.
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)
Photo 2
Photo 3
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. 
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.
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.
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.
Photo 7
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: 
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Hi,
Do you have a tip for getting a mosaic tile floor nice & flat? I’m planning in setting 12″ x 12″ sheets of 3/4″ porcelain hexagon tiles.
Thanks
Hi Len,
Yes, get a 12×12 sheet of plywood (or cut one) and lay it over the sheet of mosaics you just set and hit it evenly with a rubber mallet.
Hi Roger , I am having a big project coming on!
I would like to install porcelain wood looking tiles in my basement, since we had a flood in september,and nothing else would be permanent floor covering resistant to water.
Any way I would like to install radiant floor heating supplied by WarmlyYours company , and they are recommending to install cerazorb synthetic cork thermal barrier.
The basement floor is a u insulated concrete slab 6 feet bellow grade.
The real problem is the floor is not flat nor leveled , since it has a slope towards central floor drain , which one is in utility room.
How to make floor flat, what is your advise, and what to use to adhere cerazorb to concrete slab?
How much space should I leave between tiles and wall, what would be ideal tile spacing for unseeded grout?
Thank you very much for any answer!
Hi Zoran,
Whatever cerazorb recommends to install their product with – I don’t know what that would be. Install that, then the heating elements, then pour self-leveling cement over the top of them. You’ll need to block off the portion with the drain.
1/4″ between the tiles and wall, you also need to place perimeter foam around the room (concrete section of home depot) before pouring the slc. I have no idea what unseeded grout may be.
hi,
not true.
you can lay tile on an uneven floor (i’ve done over 1/2 already on a small room). the problem is TIME.
just have a level in your hand. you won’t be able to use a trowel to lay mortar – you’d use a wide spatula and insure it’s a little higher then neighbors, then work it down – removing excess as it goes to target height. the mortar will have to be thicker paste (less water) if the floor varies say 1/4″ end-to-end. using a wide spatula, spread mortar until even – this insures when tile is laid you get “instant full contact” (the ridges aren’t necessary – you’ll be pushing the tile like darn to level it). work the tile down until it’s level and at the height that will satisfy (being even to the lowest tile if gently stepped to). another reason the notched trowel wont help is because it only works with wetter mortar – it only messes up mortar if it’s mixed like concrete. when using non-wet mortar be aware it dries rock solid to walkable in 24 hr instead of 48, and dries when working (working time) 2x as quick.
the problem is TIME. it will TAKE WAY TOO LONG except maybe for a SMALL bathroom. each tile will take time and that means mixing mortar only 7-10 lb at a time. i’m having that problem now. multiply time times hundred(s) of tiles and it’s a big problem.
the good news is the result is very acceptable with no “tipping” – and would be appropriate for a small bathroom
you shouldn’t skip the leveling step unless you have some reason to think the extra time and effort will not over-run your benefits
would i lay a 1+1/2 ” mortar let it dry then tile over it for a small footprint bathroom (no shower). no – i’d just mix a thick paste and do it all at once, with level in hand will work
Hi John,
LOL. That’s funny, because this is a joke, right???
I would appreciate you NOT spreading misinformation on MY blog. There are hundreds of sites where the administrators don’t care what type of BS ‘method’ you throw out – I’m not one of them.
The MAXIMUM build-up thickness of ANY mortar is 1/2″, and that is a very high-end thick bed rated mortar. Most mortars have no more than a 1/4″ maximum effective thickness requirement. If you try to do a 1 1/2″ thick bed of mortar beneath your tile you’ll have issues. I’m glad you have your method, and I’m glad it works for you. And I’m glad you’ve been doing this for (insert number here) of years with no problems. But I attempt to promote FACTUAL information here and give people methods which reduce the chance of failure, not increase it. Because replacing an improper installation takes a hell of a lot more time than doing it correctly the first time.
Actually, the above is simply ONE way to do it properly, a better method is a wet-set method with deck mud, that is a more proper way for an experienced setter. Your method is NOT one of the ways.
Hi Roger,
What size notched trowel for 20″ x 20″ porcelain floor tiles? Also, any special prep if the are being installed over travertine tiles?
Thanks,
Mark
Hi Mark,
Whichever size gives you the proper coverage, I normally use 3/8″ square or larger. If what is being installed over travertine? The new tile? If so, you need to make absolutely sure they are solid and the travertine doesn’t have a sealer on it which would prevent the thinset from bonding.
Tile Elf
HELP!! i have a concrete floor and the tiles keep shifting up and down, its been weeks now thin set should be dry, and ideas to keep them from doing so?
Hi Dawn,
Yes, pull them out and have them installed correctly. There was obviously something done incorrectly with the current installation, but you’ve given me zero details about that, so I have no idea what it may be.
Hi TileElf,
With regard to the expansion space around the room, I’m confused about what materials need the space and which don’t. I am flattening my plywood floor in a few spots with thinset, then laying decoupling membrane, thinset, tile, grout. Some videos show the lowest layer of thinset being applied all the way to the wall, but the membrane and tile (and I assume grout) laid with a space. Is that okay? It seems hard to keep a space when skimming the plywood.
Also – I am installing in a small room that won’t have baseboard. Is caulk the only option to fill that expansion gap? Thanks!
Hi Julie,
It is best to have an expansion gap around the perimeter of the room for all materials. You don’t need to leave a gap in the thinset itself, it can go as far as you want (don’t worry about getting only to the edge of the gap), you just don’t want materials butted against the footer. Yes, caulk is the only option for a space without any type of base.
i have seen”zero” groutline installations in dept stores and want to
duplicate the look in a 5by 8 bathroom using 12by12 granite tiles. Can I
butt these tiles together and just wash a tiny bit of grout into the bevelled
surface edges ? Also will I have any problems cutting these tiles with a
regular score and snap tile cutter?Put down the cocktail and please give me an answer……Thanks
Hey Bud,
No, you can not. A score and snap cutter will not cut granite. If you do butt them and just fill the bevels it will crack out within six months normally.
We just had marble basketweave tile installed in our bathroom. The tile is entirely uneven and the grout covers the corners of the small square tiles. They installer said that the marble is uneven, which is why they tiles are sticking up in places. This explanation does not make sense to me 1) because they installed an entirely new floor and 2) the tile, when it came out of the box and was laid on the ground was entirely flat. Is this just a sloppy install? I want a smooth bathroom floor, but don’t want to be too picky.
Thanks.
Hi Heather,
You are not being picky – that is a sloppy installation. It doesn’t matter if the marble is uneven or not, the finished product needs to be flat.
Thanks. Do you know how difficult it is to fix the pieces that are sticking up?
What should I expect in terms of fixes? There are several cracked tiles, grouting that is missing, and tiles that are sticking up.
Unfortunately that floor will need to be removed and replaced. If it were simply uneven then it may be able to be ground and refinished (although that would likely cost more than replacement), but with the other problems it sounds like you may have substrate problems as well.
Great advice
Thanks
What are your recommendations for cutting 12×24 inch tile?
The layout I’m looking at may have a few pieces that run the full 24 inch length, but I’ll have to cut out a portion of the width to have the piece wrap around a corner. My concern is the tile will break when cutting near a narrow section of a long piece. Most tile saws I use appear to only be equipped for 12×12 or smaller, anything longer and your limited on length you can cut. Any recommendations would be appreciated
Thank you for the help. My wife and I are remodeling our bathroom and want to lay some new tile. However, I have never laid tile, so I am nervous about trying to keep it as level as you are showing. Do you think I should hire a professional to teach me how to do it? http://www.costenfloors.com/#!tile/jyy5v
Wow do I have a problem! The subfloor in kitchen had a strap that caused it to bump up but I put backer board over thinking it would be level enough for travertine tile, wrong! It still looked like speed bump and tiles cracked. I ended up pulling up 8 tiles and had to cut out backer board so new tiles could be level with surrounding tiles. Problem now is I can’t get leveling material level enough to surrounding tiles and have new tiles flat enough without them rocking. Is there something I can pour that will self level the crap I have seems to dry too fast to move around. Any other suggestions?
Hi Debbie,
Any good self-leveler will work to get it close. As you install the tile adding or removing thinset from under the tile will allow you to move the tile up or down to flush with the surrounding tiles.
Excellent !!!
Now go have a cocktail
Am getting ready to lay travertine (18×18 inch) bathroom floor..can I just butt joints or are spacers and grout a better way? Thanks in advance for all your great tips!
Hi Melanie,
You NEED grout lines.
I have applied 9×35 porcelain tile to an outside concrete porch. Used an adhesive fortified thinset. Tile are heavy so I mixed the thinset thicker to keep them from settling to much. Applied using a 1/2″ notched trowel which was recommended. Buttered back of tile but really question how thick the back butter layer should be. I estimate I put on a layer that is 1/4″thick. Seems like I used double the amount of thinset. Have I compromised the strength and durability of the tile? How thick do you recommend back buttering? By the way I used latacrete premium 254 thinset. My first tile project and it is the entry of our house. Hope I haven’t messed up. Have a back porch to do next spring with same tile and material. Will be subject to severe whether in winter.
I appreciate your help.
Hi Russ,
Backbuttering simply indicates a skim-coat of thinset on the back of the tile to ensure that all the pores, as well as any raised pattern is filled with thinset. It doesn’t have to be thick at all. Your tile is fine.
I will be installing 1000 sq ft of 6×24 porcelain tile using RLS tile leveling system and need to know how many 1/8″ clips I will need.
Thanks
Hi Mike,
Normally 4/square foot.
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
Hi Doc,
Yes, I do it as I install tile. However, if those humps are less than 1/8″ then they won’t affect your tile installation as the amount of thinset beneath the tile will be more than that.
Roger,
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,
Rob
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).
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.
Would a rubber squeegee work in this situation? Not a flimsy one like at the gas station for cleaning windshields, but a thicker one like the ones used in window tint installation.
In what situation Thomas? I can not find the comment to which you are referring.
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.
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.
Roger,
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.
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.
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.
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.
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.