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)

{ 461 comments… add one }

Leave a Comment

  • Robert

    Sorry, a bit off topic, but I was just wondering what these weird tiny little clear square flecks are on a textured, matte biege porcelain tile I was looking at. You can only see them at a certain angle and more up close, but they make the floor look slightly moist or wet when you do see them. Wondering if they’re surficially applied or some sort of glaze reduction. I can supply a photo if interested. I’ve never seen tile like this before, though it’s a very ordinary non flashy tile. Wondering how they got this effect and if there might be cleaning problems with this kind of tile.

    • Roger

      Hi Robert,
      If they are floor tiles they are likely placed there to increase the grip of the tile so they are not so slippery. If they are not floor tile then I need a photo to see what you’re describing. You can email it to Roger@FloorElf.com.

  • Dimitri Katsaros

    On my last project I used precisely this method to great effect.

    I’m wondering though… is there any benefit to using “tile leveling systems” by Raimondi, Levtec, and the like? I only ask because I’ve found no mention of this type of spacer/leveler on this site.


    • Roger

      Hi Dimitri,

      They do work well for large format tile. I use the MLT system for anything larger than 2×2 or any rectangular tile larger than 12×24. They are really good at keeping the tiles flush while the thinset cures.
      They do not make up for improper installation techniques, nor do they eliminate the need to get the tiles flat as you’re setting them. Think of them like a clamp for tile, so the tile remains where you put it as you’re setting it.
      The reason they work so well for that is that mortar shrinks as it cures, if you have more mortar beneath one tile than you have under the tile next to it, the one with more mortar will shrink more, drawing the tile slightly lower than the other. These systems keep them locked together so that doesn’t happen.
      The main reason I don’t have anything here yet is that a lot of people think they eliminate the need for proper setting technique, which leads to a lot of problems like tiles with not enough mortar or incomplete coverage.
      They do work well, though, if utilized as what they are, a tool to keep tile stable and even while the thinset cures.

      • Dimitri Katsaros

        Thanks! One thing I’m finding out with wall tiles – like the subway tiles I’m installing – is that while I can get them installed with no perceivable lippage, they are definitely not dead flat. Thank goodness I’m not doing a layout with an offset or I’d be going nuts. The manufacturer suggests not doing more than a third overlap and now I know why. Porcelain tiles are definitely not like the stone tiles that I am used to in this regard.

        • Roger

          Yup, every manufactured tile has cupping to it due to the annealing process in the manufacturing. Natural stone tiles are cut to size, so they can be exact, manufactured are cooled to size, they vary.

  • Walter Greenwood

    “Swirlie” is, indeed, a word, but not one you should use at a polite dinner party with your mother. It refers to a particular service you might receive from a significant other if you are lucky. However, if you pay someone to do it, you might get arrested. Just saying.

    Thank you for your website. I’m learning more than I ever wanted to.

  • Garrett

    I wasn’t sure if my comment belonged in the flat vs level article, but based on the other comments I’ll put it here.
    Do you have a sort of threshold where you essentially determine that maintaining tile lippage ad hoc like you describe in this article isn’t worth it and go with a SLC? Obviously the skate park reference is fair, but lets say you want to tile on a concrete slab that’s “borderline” acceptable – what would be a grey area for you? One section of the slab that has a 1/4″ offset? 10 areas with 1/8″ offset? Raised area around a toilet flange? I imagine there’s some threshold where using your MLT system and ad hoc thinset application just won’t be enough to compensate. At what point do you make that decision to throw down a SLC? Or possibly never and you prefer to grind down the concrete? For the sake of the question assume a LFT install.

    P.S.> some folks recommend grinding concrete not just for flattening, but also to prepare the surface for proper bonding, especially if there was some sort of linoleum, adhesive, or protective coating on it prior. Thoughts? What about a chemical cleaner like TSP instead of grinding? Is there a concern in changing the surface such that thinset won’t get a good bond? Or cleaning for a SLC underlayment if you choose to use one?

    • Roger

      Hi Garrett,

      Acceptable tolerances (per TCNA) are less than 1/8″ in any 10′ area or less than 1/16″ in any 24″ area. I normally bump that up a bit if using an LFT mortar, but not much. With the variation you’ve mentioned I would use an SLC, especially with an LFT.

      A general rule with bonding is to splash some water on the concrete. If it soaks it in readily then thinset will bond readily. I will normally grind to do this as I’m not a fan of chemical etching for that purpose (although it does work, that’s just my preference). If you do use an SLC then go ahead and use the primer over the concrete, whether it soaks in the water or not. The primer will create a rough layer for the slc to properly bond, then the thinset will always properly bond to the slc.

      • Garrett

        Nice one! Thanks Roger!

  • Al

    What about leveling systems and which one would you recommend? Especially for long wood look plank tiles.

    • Roger

      Hi Al,

      I use and recommend the MLT system.

  • Paul

    Hi, I wanted to ask what the best saw was for cutting porcelain tiles without any chips. A cut good enough to be installed on the middle of the floor and not hidden at the edge. This cut is for a border to be installed. Small chips on a tile wood ruin the job

    • Roger

      Hi Paul,

      I isn’t so much the saw, although that plays a part (I use the DeWalt), it’s the blade that is the biggest factor. You will never get a blade that leaves absolutely no signs of chipping. A blade made for glass is the best (yes, it will cut porcelain as well). Once you make the cut run a rubbing stone down the edge and you can normally get a smooth edge with no signs of chipping.

  • Elaine

    Hi, I need your guidance. We are installing wood like tile, 8×48 rectified. My husband has told the installer that he does not want a grout line…I am begging that he does at the bare minimum a 1mm grout line, but he has already laid out 1/2 of the room. Am I overreacting or will it be okay if he can keep the lippage to a minimum. He does plan to grout to fill in any gaps at the end. What are your thoughts?

    • Roger

      Hi Elaine,

      You likely already know my thoughts – you NEED a grout line. Even 1/8″. Especially with tile that size. I would refuse to do that project, and have done so seven times with people who insisted on no grout lines. It *may* be okay, but will likely have issues (chipped tile, tenting, debonding, etc.) long-term. You also didn’t mention how large the room is, it NEEDS a soft joint as well, you can’t do that without grout lines.

  • Dan

    Hello Roger,
    Love your information & the humor is spot on !!!. My better half and I are doing our second rebuild on our second home. We’ve laid 13”x13” tiles in our old kitchen with a straightedge with 1/4” grout lines and had one lip in the whole thing, “to many hours in one day”. Both kitchens were and are galley kitchens, this one is 10’x40’ including a laundry room at one end. we are going to lay 20”x20” porcelain tiles “pavers I guess they’re called” with 1/8” grout lines. Would you attempt to straightedge tiles this big or would you use the MLT system on them and is 1/8” grout lines ok on tiles this big.

    • Roger

      Hi Dan,

      Provided the size variation in the tile allows for 1/8″ grout lines it will be just fine. Yes, I would use MLT on tiles that large. It just makes the installation so much better and takes the guesswork out of whether the mortar beneath a certain tile will shrink too much while curing and pull it down out of flush. It locks everything in place while it cures. The amount of mortar beneath tiles that large can create issues with shrinkage, creating lippage where there was none while fresh.

  • Kim

    I have appreciated your tile tips!

  • Royce

    Hi, Just wanted to say thank you for the great advise above, I’m about to embark on some floor tiling in the laundry and then kitchen and was feel’n stressed about it, I’ve done DIY stuff but never tiling and was glad I stumbled across your article.

    OZ Down Under.

  • Eloise

    I had someone Tile our bathroom floor. The travertine isn’t flush in a few spots. Are there anything I can do to correct this now??? Please help

    • Roger

      Hi Eloise,

      Unfortunately not really. Once it’s set and cured there is very little you can do to remedy any lippage issues. It is a natural stone so it CAN be refinished (sanded down and polished), but it is something that absolutely needs to be done by a professional and will cost you more than the initial installation. Can you get that person back to remove and replace the tiles in those spots? That’s about the only thing that can realistically be done.

  • Jorge

    Roger, thanks for all your effort and time. I was always taught to follow the tile when installing it so taking that into consideration i am tiling from the doorway in. So the question is, can i tile say “half-way” and leave my self an out of the room and come back 24hrs later and finsh up the rest or is it better to tile the entire floor at the same time. Thanks

    • Roger

      Hi Jorge,

      It is always best to do the whole thing at once, but there’s no reason you can’t do half at a time. You just need to ensure you have your layout nailed if you do that so there are no surprises when it’s too late to change anything the next day.

  • Joe

    I’m tiling a small bathroom. 40sqft. It slopes down back to front and left to right. After all that sloping the highest corner is 1/4 higher than the lowest corner. Can a trowel make up this space difference alone? I’m using lft cause it’s 12×24 tile and was planning on using a 1/2×1/2 trowel. I’m just thinking if I use a 1/2×1/2 trowel on the high end by the time I get to the low end the trowel won’t be able to compensate for the 1/4 slope. Would I trowel the backside of the tiles in lieu of the traditional backbuttering? Would I switch between 1/2 trowels and 3/4 trowels throughout the job?

    • Roger

      Hi Joe,

      Yes it can make up for it. Just add more thinset to each tile as you get towards the lower end of it. You do know you don’t have to have a LEVEL floor, right?

      • Joe

        I know as long as it’s flat. I do have a couple of humps from the joints of the durock in the center of the room. I could probably sand them down and then it’s a steady constant decline. Say I ignore the level ness and just use my 1/2 trowel and my lash tile levelers. Would I just work from the highest point down to complete one whole column of tile then move to the next column til it’s complete. Working column to column. That’s kind of how the slope is leaning

        • Roger

          If it’s flat it really doesn’t matter much what order you install it. If it’s a consistent lean that may be a bit easier, but if it is indeed flat then consistent troweling will keep it flush.

  • Kevin McGreevy

    Hey Roger,
    With, seemingly, every designer now in love with massive tiles- LFT, I’m about to jump into a leveling-system. Still use the old spirit-level, er straight-edge. Don’t know if you have jumped into these, but if you have, do you have a difficult time justifying to the client the additional expense of the clips ( @ 1-3 clips/sf and 15-20 cents a pop). Or justify the expense with a “perfect ” set outcome. I can see where you can get a faster install with some obstinate product, but better-for the price? Just don’t know. Whatcha think?

    • Roger

      Hi Kevin,

      I use the MLT, and they are worth every penny. I do not justify my prices to anyone. This is what they want, this is what I charge. They can feel free to take it or leave it. Stop trying to justify your job to people hiring you to do the job – you’re the professional. :)

  • ken

    Hi, very interesting tips! I know this technics but sometimes it happen sometimes that one tile are not perfectly flush and I hate that because it’s even when I leave the job and when I comeback the next day it look like it move when the thinset dry, even if it’s just a little bit uneven. It happen with 24×24 as well, I was about to use the little plastic leveling system they sell at homedepot but I don’t know if it’s a good product, not sure if pro’s use that ? and even if the plastic leveler equalize the tiles it’s not garantee that you have put enough thinset everywhere beneath so the plastics leveler do the bridge leveler between tiles but how we know there’s no ”bad support” beneath the tiles if it’s the plastic leveler who hold tiles together and not the thinset like it’s suppose to be ? Thanks

    • Roger

      Hi Ken,

      The LASH system (home depots system) works, but it’s definitely not the best. Pros do use lippage systems. With the manufacturing of tiles as it is now it is EXTREMELY difficult to get tiles flat enough to do an offset and have it flush without some type of system in place. These systems DO NOT replace proper installation techniques. You need to set the tile as you normally would, get them even, then tighten the straps down. They are a clamping system – to hold the tile in place as the thinset cures. They are not an installation system used to get your tile flush as you set them. They should be flush before tightening the straps. That being the case, you will have adequate thinset beneath your tile, the clips and straps should not affect that at all.

  • David S

    Can my condo floor – which is ~1-1/8″ out of level from one side to the other, but less challenged in regards to flatness – be brought closer to flat/planar using “self-leveling” compound, but working the stuff purely by screeding, maybe mixing it a bit thicker than normal? (I don’t *want* it to go “level” on me this time.)

    I’m thinking I’d feel better about getting as close as possible to flat, before laying thinset, since the alternative of the trial-and-error process of building up thinset at lower parts of the floor seems like it would be quite fatiguing and prevent getting into a groove…

    Also – how do you prevent discovering, halfway through a room, that the top plane on which you’d been setting tile turns out to run into a high area of the concrete subfloor? I’m guessing it’s pretty important to figure out where that high-point is to begin with, and start setting tile close to it (or grind it down) – but finding that location seems not trivial when there’s no “level” in the equation.

    I guess I shoulda kept my old non-self-leveling laser-plane?!

    • Roger

      Hi David,

      You can not screed slc. Using a medium-bed mortar (or LFT mortar) with the ‘trial and error’ method is about the quickest way.

      To find your highest spot – you need a laser level. Set a bucket on what you believe your highest spot to be, then make a mark on the laser line. Leave the laser where it is and move the bucket all over the room. Provided the laser line does not go below your marked line – that is indeed the highest spot.

  • Nolejoe

    Just use clips then you have no lippage if you don’t do this 52 weeks a year

    • Roger

      Hi Joe,

      I do (use clips, and do this 52 weeks a year). But this site is mostly geared towards diy’ers. Doubtful they have the ability to drop a grand on the system I use when doing a small bathroom. :D Plus, most (even professionals) don’t seem to understand that these systems STILL require every other aspect of a proper installation, they just take out that last very little bit. It still needs to be installed flat and correctly.

  • Roger

    Hello Roger,

    Which tile is the first to get set down? In the middle as I’ve seen some videos or towards the edges of the room? I have a layout chosen; where smaller cut tiles and uncut tiles go, but I’m not sure how to get started on this project stage (ditra is down and we’ve addressed peaks).

    Thank you!

    • Roger

      I start in the corner furthest from the door. But you can start anywhere you want.

      • Roger

        Ok, that sounds great, but what happens as I fill out the room towards the door? When I reach the door, I will have a space less than the complete width of another tile, which means I need to insert a row of cut tile at the door. Is this ok?

        • Roger

          Yes. Or do your layout so you have a full tile in the doorway. You didn’t ask where to start with a full tile. :D

  • Roger

    Nice name, first off, and second, I love the post, thank you. I am working with the mrs on our first travertine tile project in our bathroom and we’re both learning how to do all this work ourselves. We have a wood subfloor and have placed shluter ditra on the entire space. Now, as I learn about preparing for laying tile, I came here and read your great post. My question is… how do I properly deal with slight peaks and valleys on my ditra? A little extra thinset for the valleys, but what do I do with the peaks (a little bump showing under the ditra)? I had the idea of cutting the ditra around the bump, sanding it down, and replacing the ditra in that shape. Is this ok?

    Thanks again for helping us noobs.

    • Roger

      Hi Roger,

      Yes, you can remove and sand, then replace. And yes, more thinset beneath the low areas. If your peaks are less than about 1/4″ difference from the plane you actually don’t need to do anything to them, the trowel size and amount of thinset it leaves will compensate for those areas.

      • Roger

        hi again, Roj! Thank you for your help so far. Last night, the mrs and I dry fit a few 18×18 travertine tiles in our walk in closet (adjacent to our bathroom, which also is getting tile). The room is 93 inches wide by 137 inches long. Placing tiles across the width, I can fit 5 tiles, with .16 of a tile left over. If I split that difference, (to divide evenly between the 2 walls that run length wise, this doesn’t give me much stone to cut and place. I am afraid I cannot cut that slim a width of stone tile, or can I?

        I do have 1 inch of baseboard (.5 x 2) to replace once the time is in place, so would you recommend I try absorbing that space somehow, or do you believe I can and should cut stone to fit there?

        Thanks again :)

        • Roger

          How big are your grout lines?

  • Helenn

    Roger I love your tutorials and diy help! I used to install 12×12 ceramic about 15 years ago as a job. Not so much anymore. I just bought 12×24 porcelain tiles for a bathroom. Small but they’ll look nice. I’ve seen the 1/3 rule for layout but how do you do this and where do you start your first row? I have to work from bathtub to door and will run the length of the tub. Also, 1/4″ spacing ok for grout lines on these? I bought mortar for porcelain tiles as this seems to be a thing now but I now see others recommending a large format mortar? I have maybe 30sf to install but I want it done right! This is my forever house after all! Thanks!! Just haven’t worked with this size or porcelain!

    • Roger

      Hi Helenn,

      1/4″ spacing is HUGE. I normally use 1/8″ on floors. I start my first row so I have a full tile in the doorway and work back from there. Just offset the second row 8″ from the first. The porcelain tile mortar that you have is a large format mortar, so you’re good.

    • Luke Elliott

      1/8 space or less is best. Start from most visible corner and continue around corners with the remainder of cut peices. Alternatively start in the middle of dominant wall for even corner cuts on that wall

  • Mike

    I’ve searched your website and haven’t found the answer to this question. Is there a preferred direction (technical, not aesthetic) when laying 12×24 rectangular porcelain floor tile in relation to the floor joists (assuming properly prepared sub floor and base)? Should these tiles be laid with the long edge perpendicular to the joists or parallel? Thank you again for your help!

    • Roger

      Hi Mike,

      It makes no difference at all which direction you run it.

  • Kev

    Finally someone who uses the words “straight-edge” not “spirit level”! I read a few “how to lay tiles” articles and watched videos and they all said “use your spirit level” I was pretty sure the really meant straight edge but they never explained what they meant. I kept having visions of novice’s actually using it as a level and by the time they finished the tile adhesive was about three inches thick on the other side of the room. I admit I did struggle with leveling 6 inch quarry tiles.

    • Bry

      Yeah, Kev…I’m finding myself in that “novice” category problem. I’m tiling a 20′ by 20′ room using 6″ x 36″ tile. I started in the middle of the room, and I have approximately 4-5 feet more to go on one side and my thin set is at 3/4″. I started with 1/2″ trowel. I used my 6′ level and everything looks good, but I’m having to increase my thin set. I’m getting a bit concerned. Luckily, this is a three season room, so I have plenty of door clearance. Looking at the overall job, it’s looking nice- just getting concerned (and found your “spot on” comment). Do you have any suggestions? Should I start gradually decreasing the thinset? Thanks in advance. Anyone else with suggestions, please feel free with advice. Large area- with big concern. Please help.

      • Kev

        Hi Bry, sorry, I’m strictly a novice myself, I just kept seeing this crap about “spirit levels” and thinking someone’s going to come a cropper one day. If I was in your shoes and it was too late to start again I’d go with what you said and try reducing the thickness as you continue. You’ll probably be the only one who ever notices any discrepancy.

  • Rick

    Huge fan, and glad to have found your site. Quick question or two, I’ll be using a speedset mortar to set a two-tile pattern in an entryway (6×6 & 1×1 inch tiles). This thinset specifies light traffic after six hours, groutable in two. If the material does takes six hours to develop enough strength to withstand foot-traffic, why am I not concerned with my body weight on the tiles four hours earlier to grout?
    Secondly, if one were to grout prior to six hours of curing, should an installer use for ex. a board to spread his/her weight over a larger area to be safe? Or is it no real concern? Much appreciated!

    • Roger

      Hi Rick,

      You should be. See, in the manufacturing world they have this magic grouting technique where they don’t put any weight on the tile at all. It’s a miracle! :D Yes, a board would work best. The biggest issue is sideways force on the tiles, sliding them out of place by sheer force, not necessarily the weight on the tile.

      • Rick

        Ok good deal, thanks for confirming! And now that I can be confident that method will work, I won’t have to wait 6 hours 👍 (6 hours of wondering if I could have gotten away with jumping on it sooner… figuratively… … and believe me that “weightless grouting technique” had me puzzled…) To be on the safe side I feared I’d need to just assume the two-hour mark only referred to when the mortar would be “ready” for exposure to other materials (namely the water content of fresh grout) without compromising the cure- am I close on that? feel free to correct me, this is for posterity after all, but since I just couldn’t be bothered today to dig through the lit’ looking for the strength gain ratings for this material to figure it out for myself, your input is very much appreciated. And so thanks again, and also for replying quickly you’ve saved me some time!
        -a fan. Figuratively

        • Roger

          Two hours is the amount of time that compression strength will not be compromised. There is still the risk of sheer by placing lateral force on the tile (because people can’t pick up their damn feet when they walk), it takes six hours to guarantee that won’t be affected.