The days of grabbing a three dollar bag of “thinset” and sticking floor tile right to the plywood in a bathroom are long gone (for professionals, anyway). For a proper tile installation you need a proper substrate. One of the most readily available are cement backerboards.  These include products such as Hardiebacker, Durock, Fiberboard, wonderboard and a host of others.

When properly installed on your floor it is an ideal tile substrate for a quality and lasting installation. Notice I said typed “properly installed”? Laying them down on the floor and shooting drywall screws through them does not constitute proper installation.

Choose your weapon. I prefer Hardiebacker or Fiberboard. Whichever you choose make sure you get the proper thickness. With rare exception the 1/2″ variety would be the best choice simply because I like to overbuild stuff. With proper floor framing and deflection ratios, though, you can use 1/4″ to minimize height differences. This is not to say that 1/2″ adds significant sturdiness to your floor – it does not.

Dry fitting Backerboard on floor

Dry fitting Backerboard on floor

You need to realize that cement backerboards, or just about any tile flooring substrate, does not add deflection stability to your floor. That is the up and down movement in your floor when you walk, jump, or use a pogo stick on your floor. The backerboards will not significantly diminish that movement. This needs to be addressed by adjusting your floor joists and framing – not by adding stuff on top of them. If your floor is bouncy without the backerboards it will still be bouncy with them.

Bouncy is not good for tile. (There’s a sentence I never thought I would say type.) I will, however, address deflection ratio in another post.

Start by ‘dry fitting’ all your pieces. This simply means cut and lay your pieces into the room without attaching them. Get all your pieces cut, holes cut out, and doorways undercut to fit and lay everything in there just like it will be when installed. This saves a load of time, mess, and headaches.

Backerboards dry fitted into room

Backerboards dry fitted - notice gaps in seams

The joints in backerboards should be staggered. that just means that none of the seams should line up across the room and no four corners should be placed together. By staggering the seams you add strength to the installation simply by not having a significant weak point in the substrate.

You also want to leave 1/16 to 1/8 inch gap between each sheet – do not butt them together, and around the perimeter. If you butt them together you leave no room for expansion. The backerboard will not expand, but your walls will. If everything is butted tight and your wall expands into the room guess what happens. That’s right, your dog may burst into flames and no one wants that! It will also cause your floor to pop loose and possibly ‘tent’ or peak at the seams.

Beneath the backerboards you need thinset. Just about any thinset will work but you need to have it there. skipping this step virtually eliminates the purpose of preparing your substrate for tile – you may as well go grab that three dollar bag and start setting tile now. You need it – really.

Installing thinset beneath backerboards

Installing thinset beneath backerboards

Now that you have them all laid in there properly pick one side of the room to start on and pull a row out. You should only pull out one row at a time to place thinset beneath. That way you can replace them easier and in the proper position. If you pull out the entire room you may get to the last piece and discover everything has shifted 1/2″ and the last piece needs to be cut again. Not really a big deal but you won’t realize it until the backside of it is covered with thinset and you now need to pull it up, wipe the thinset off the wall from pulling it up, cut it, clean the thinset off your saw, snuff out the flames engulfing your dog (again), and replace it. It’s a bit easier just to pull one row at a time.

You need to trowel thinset onto your floor. I cannot overemphasize this (well, I could but you’d get sick of hearing it). This step is imperative for a proper tile installation. The thinset is not meant to ‘stick down’, adhere, or otherwise attach your backerboard to your subfloor. It is simply put in place to eliminate voids beneath your backerboard. Once laid into the thinset bed the floor becomes a solid, fully supported substrate for your tile – that’s what you want.

If you have an air pocket or some certain spot in your floor that is not level or flat with the surrounding area and you simply screw your backerboard onto it this will create a weak spot in your floor. Constantly stepping on that spot will, over time, loosen the screw and your floor will move.

When your floor moves your grout cracks. When your grout cracks your tile may become loose. When your tile becomes loose your tile may crack. When your tile cracks your dog will burst into flames – again. Put thinset beneath your backerboard. And put your dog out.

Installing thinset beneath backerboards

Installing thinset beneath backerboards

Once you have the area fully covered with thinset you can lay your backerboards into the bed of thinset and screw it down. DO NOT use drywall screws! Let me repeat that – THAT! Drywall screws are not made, nor are they sturdy enough for your flooring. You will either bust the heads of the screws off or be unable to countersink them into the backerboard. Hard to get a tile to lay flat over the head of a screw.

There are screws made specifically for cement backerboards. You should be able to find them at any hardware or big box store. They have grooves on the underside of the head which will dig into the backerboard and create its own ‘hole’ in which to countersink the head as it is screwed in. How cool is that?  If you look closely at the photo you can see the ‘grooves’ beneath the head. They are more expensive than drywall screws – just so you know. But you need to use them.

Backerboard screw packEach manufacturer has their own specific spacing instructions for screwing down the backerboards – follow them – really. Some say every 12″ and some want every 6 – 8 inches. The board you use will determine the spacing. (And its right there on the sticker so don’t tell me you couldn’t find it.)

Start your screws in the center of the board and work out. This eliminates undue stresses on the boards. If you screw all the way around the outside and it is not perfectly flat you are going to have to release that pressure somewhere and it

Backerboard screw

Backerboard screw

won’t happen until you have all that pretty tile on top of it. Working from the center out eliminates that. It would probably never, ever be a problem but if you’re anything like me your installation would be the millionth one for that one in a million occurrence.

Backerboard placed into thinset and screwed down

Backerboard placed into thinset and screwed down

Your floor is probably too thick (should be) for the backer screw to actually penetrate into the floor joist. If not, or just to be safe, do not place screws into the area above the floor joists. The plywood or chipboard which makes up your floor will expand and contract at a different rate and, more than likely, in different directions than your joists. If you screw your backer into the ply and into the joist six inches over it will cause inconsistent movement – no good. Do not screw your backerboard into your joists.

After I have all my floor down I will go back and double the screws around every seam. Just put another screw between every screw along the seams. It helps me sleep better at night.

The last thing you need to do is tape your seams. Get an ‘alkali resistant’ mesh tape – similar to drywall tape – and place it over all your seams in your floor. Then mix up some thinset and trowel it over the tape with the flat side of your trowel. Just like taping and mudding drywall. This will make your floor one large monolithic structure and lock it all together. You want alkali resistant tape so it will not break down due to chemicals present in most thinsets. I do not have photos of this because I do it as I set tile.

That’s it! Congratulations, you now have a perfect floor for your perfect tile installation. When installing floor tile – or any tile for that matter – the most important aspect of the installation is always the preparation. Everything beneath your tile is important, if any one aspect is done incorrectly it may compromise the integrity of your installation. Take your time and do it correctly, you will be much happier for it.

Now go put your dog out.

{ 1721 comments… add one }

Leave a Comment

  • Eric

    Hi Roger,
    I was wrong and instead have porcelain tile. Can I still use versa-bond thinset.

    • Roger

      Yes.

  • Eric

    Hi Roger,

    I have the mapei ceramic tile mortar and some versabond which I used under my backer board. Which would you prefer for laying my ceramic tile down with. Also should I back butter my tile. They are 12×12.
    Thanks

    • Roger

      Hi Eric,

      Either will work just fine, always backbutter.

  • Greg

    I removed tile from my master bathroom floor. The tile just popped off the existing cement board so I was able to save the cement board. It looks like the original tile was set in some sort of tan mastic. The house was built in the mid 90’s. The substance is hard but it is relatively flat. I fair small trowel was used. Can I just use thinset over this?

    • Roger

      Hi Greg,

      If you splash water over it and it soaks into the board within a minute, then yes, you can use thinset over it.

  • Noel

    Roger,

    Thank you for creating one of the best tile sites on the web. I can’t even begin to tell you how much I’ve learned from this site.

    Okay, so I want to install a ditra heat system in my bathroom that I’ve been working on for about a year. Don’t ask why it’s still not done.

    My 3/4 inch subfloor was cut up like swiss cheese and has some uneven areas. The folks at Schluter said I could not use Ditra heat on cement board. Schluter recommends Ditra heat on the following substrates: wood, concrete, and gypsum. Really…drywall on a floor…that makes no sense to me.

    It just seems logical to me to lay cement board and then the Ditra heat. I was thinking the following:

    1. Thinset cement board to wood subfloor
    2. Use SLC to get floor perfect flat
    3. Thinset Ditra heat
    4. Install tile and done…

    Honestly, the ditra heat system seems to be great. However, the damn testing tool needed to perform the three tests costs about $500.00!

    • Roger

      Hi Noel,

      I have not heard of the limitation over backerboard, I’m currently trying to get clarification on that.

      I would just go with an additional layer of 1/2″ plywood, it would actually give you more stability than cement board. Go right over that. Ditra heat is the way to go! And yes, the cost of the tool sucks, but you may be able to rent one if you call around. A regular voltmeter will check two of the tests, the third is what you need the expensive one for.

  • Karey

    Hello! Curious if it is necessary to use cement backerboard on a concrete subfloor? We are laying porcelain tile in our small bathroom downstairs. Thanks for your help!

    • Roger

      Hi Karey,

      No, you do not use backerboard over concrete.

  • Eric

    Do I need to put thinset in between the backer board before I put tape or leave a gap for expansion

    • Roger

      Hi Eric,

      Thinset between the boards while taping and mudding, open gaps around the perimeter for expansion. You want the entire floor to move as one piece, you need the perimeter for it to move into.

  • Shane

    Hi Roger sir

    You might be right but I put thinset under backer board and it’s the only one that ever cracked on all the seems every three by five feet. It seemed like a lot of extra weight to. Got a question for you Will anti fracture membranes like redguard keep tile from cracking over backer board?

    • Roger

      Taping and mudding the board seams prevent it from cracking. Putting thinset beneath that installation did not cause it to crack. ALL these steps need to be done to ensure a proper installation.

      Yes redgard will help, but there still needs to be thinset beneath it, and the seams need to be taped and mudded. Redgard and other elastomeric membranes were originally created as anti-fracture membranes.

  • Tom

    Hi Roger

    I’m installing a tile redi shower base in my bathroom. From what I’ve been reading that may have been a bad choice. Sounds like setting it solid is a bit of a pain. I read that one guy had good luck setting right on top of the backerboard. What’s your thoughts? Any expansion issues or anything? I’m using 1/4″ backer. Also I wanted to ask if you thing redgarding the floor as well would be worth the effort/expense?

    • Roger

      Hi Tom,

      Tile redi pans work just fine, you just have to pay close attention when installing them. Setting them over backer seems to be easier for people, but not really necessary. No expansion issues once in place. Redgarding the floor (of the pan, I assume is what you mean) is not necessary.

  • Shane

    Liquid nail is the best to use under backer board. Thinsets like versa bond DO NOT BOND TO WOOD. U want a solid bond to the wood the backer board screws is the way to go though and versa bond is great for setting tile to backer board and concrete not wood fYI. THANKS!

    • Roger

      Hi Shane,

      Not for a tile installation it isn’t. While I appreciate your opinion, it’s incorrect. Had you actually read the post above you would have noticed this:

      “The thinset is not meant to ‘stick down’, adhere, or otherwise attach your backerboard to your subfloor. It is simply put in place to eliminate voids beneath your backerboard.”

      It is not meant to bond anything, simply to fill voids. The fasteners umm…fasten it to the subfloor. If you are using liquid nails beneath your backer I suggest you stop doing that – you’re actually CREATING voids beneath your tile substrate.

  • Nick

    Roger,

    No need to answer my previous question below. I got it figured out. Thanks!

    • Roger

      Okay, I’ll send you a bill since I already did. :D

  • Michael

    Very informative and sounds like you know what you’re talking about.
    My entire house upstairs is carpet and I’m replacing kitchen, living room, dining room, hallway work 8mm laminate.
    I’m leaving bedrooms carpet and putting 1/4 tile in bathroom. I want to do right so I bought 1/4 backer. My concern is 2 layers of thinset, backer board, and tile are going to be much higher and won’t look good. I think the carpet bedrooms will be close with transition board in threshold. I’m wondering if I should raise entire floor maybe 1/4. I’m just nervous about starting and not doing it correctly. Only stupid not to ask.Ty for any reply.

    • Roger

      Hi Michael,

      Regardless of how much higher the floor may end up NEVER compromise your tile substrate to meet up with existing flooring, they make thresholds for that. The layers you speak of will only be about 3/4″, hardly ‘much’ higher than the carpet. Unless I’m misunderstanding something. I may be, since you stated raising the floor 1/4″??? If you’re talking about the tile floor – just use 1/2″ backer instead. If you’re talking about something else you’ll need to let me know what that is before I polish off this 12-pack. :D

  • Nick

    Roger Sir,

    Turns out Ditra XL only comes in 175sqft rolls and I need about 45…so I am switching gears and considering Hardiebacker for bathroom floor because I want to match an existing floor height as close as possible.
    I already bought the thinset for a Ditra / Kerdi job (Laticrete 317 for the Kerdi and tile over Ditra and Laticrete 254 for under Ditra to OSB).

    I still intend to build a Kerdi shower, so I will keep the Laticrete 317 unmodified. Should I return the Laticrete 254 and use a much cheaper thinset for HB board to OSB? If so, what do you recommend? Mod? Un-Mod?…how bout Versabond from Home Depot?

    • Roger

      Hi Nick,

      The versabond is fine beneath your backer. The 254 is great between your backer and tile.

  • George

    Our condo has concrete floors/ceilings. Most people have used quarter-inch cork as the substrate for their tile. This doesn’t eliminate the noise very well. Is there a better product? Thank you…

    • Roger

      Hi George,

      A thicker or double layer of cork works well. There are many sound isolation membranes out there, as the effectiveness goes up so does the price. An effective and mid-range option would be cork combined with Laticrete 125 sound isolation mortar.

  • Missy

    Use or replace backer board under tiles I removed in my bathroom.

    • Roger

      Hi Missy,

      It depends on what shape your backer is in and whether or not it’s installed correctly.

  • Corey esamann

    Hello,

    Great article!! I have a few questions and I would love some feedback.
    1. I pulled up the ceramic tiles in my bathroom and there is 1/2″ backer board under it, thunder to the plywood. Can I reuse that same hardi backer OR should I pull it up and replace?
    2. How can I identify where my floor joists are without pulling up the plywood subfloor? I want to avoid putting screws into the joists as you state above
    3. If I am not cutting or causing dust from pulling the hardi backer up, do I need to still wear a pricey respirator? Or can I go without and just be careful and pull it up in pieces?

    Thanks so much!!!

    • Roger

      Hi Corey,

      1. Provided there is thinset beneath it (I assume that’s what ‘thunder’ meant :D ) yes, you can use it.

      2. Pull up your heater vent, find the joist, measure every 16″. Or just use 1 1/4″ screws.

      3. No, but it doesn’t hurt. A regular dust mask is better than nothing. You can’t always see the crap you’re breathing in.

  • Al Foley

    I wished I had read this post prior to doing my floor, I did not know I could set my dog on fire but we had his service this morning, we had the service outside in the rain because it was unsafe to walk on the floors in the house due to all the cracks. My wife filed for divorce following the service and my best friend is suing me cause he tripped on my cracked tile floor and broke his leg…I am going to set fire to the house now….

    • Roger

      Well, that’s a bit extreme. I’d burn down the neighbor’s house instead. The floors can be fixed. :D

  • David

    Can cement board (Durock or Hardy Board) be laid over existing tile? Is this goofy or common practice?

    • Roger

      Hi David,

      No, it can’t. You can use a product like greenskin over existing tile, though.

  • Chuck

    FE, thanks a bunch for writing and helping us. Do you use the same thinset under the backerboard as you use to actually set the tile(s), or are these different types of thinset/mortar for an important reason. I see above that you say just about any kind will do under the backerboard. I’m assuming it is because of your other statement that the purpose is not for bonding, but just to fill voids. Therefore, would I be safe to assume you care much more about the specific kind used for bonding the tile?

    • Roger

      Hi Chuck,

      Yes, I care much more about the thinset used for the tile. :D The stuff I normally use for tile is upwards of 30-40 dollars a bag, which is why I normally use the 12 dollar a bag stuff for under the backer. But you can always use the same under the backer if you want to.

      • Chuck

        Thanks, Roger. I called Laticrete and they recommended 253 Gold for my 12×24 porcelain tiles over 1/2″ Durock in a laundry room. I hope the benefits are worth that price… “Gold” indeed.

  • Chad

    Excellent article. I came by your site and info by chance. I live in a late 1800’s home and i am refurbishing a bathroom that i am going to place tile on the floor. current floor in 2 3/4″ thick. I have joists exposed as some repairs need made. Joists are 18″ apart. I have looked over lots of info here but have not seen if OSB is okay. Here are my thoughts…

    If I start with 2 sheets of 3/4″ OSB(only first layer screwed into joists), then 1/2″ plywood, then 1/2″ backer board and finally 1/4″ tile.

    another question is obviously the thinset will add to my height. should I reduce a layer of OSB or plywood to compensate for it?

    • Roger

      Hi Chad,

      OSB is fine. You need both layers. You can use 1/4″ backer on the floor rather than 1/2″, that can compensate for any height differences.

  • Tim

    Best article I saw on floor tiling with cement board. One sub-step I would like answered, Is it proper to let the backer board screwed down into thinset to dry in place for the day and then come back next day with mesh tape and tile, or is that unnecessary and just do whole job at once?

    • Roger

      Hi Tim,

      You can do it right after, the next day, or as you set the tile. The timing of it doesn’t matter as long as it’s done.

      • Norm

        Hi Tim. Roger stated in an earlier post that he prefers to mesh tape while laying tile. I highly suggest that you follow that advice. When I mesh taped a day or so in advance of laying the tile I noticed that the tape and thinset combo created a slight ridge (hump) that I had to account for when laying tile. I did my best flattening the taped seem & thinset but when it dried there was a detectible ridge.
        When I mesh taped as I was laying tile and as Roger stated, the tape as you go process resulted in one even plain without any ridges.

  • Norm

    Hi Roger. I am working by myself laying 3’ X 5’, 1/4″ HardyBackerBoard using applying Flexbond quickset with a 1/4″ notched trowel.
    1.) How long can the board lay on top of the quickset before I have to apply the Buildex Backer-on 1 1/4″ screws?
    2.) Do I have enough time to layout thinset for two or more boards before applying screws?
    3.) Since it takes me about 20 minutes to screw down each board can I cover any leftover thinset to prevent it from drying out for 30 – 40 minutes?
    3.) After 30 – 40 minutes of fastening the screws, Can I mix subsequent batches of thinset in the same 5 gallon bucket or do I have to thoroughly clean the bucket first before mixing the next batch?

    Thanks Roger

    • Roger

      Hi Norm,

      1. It can lay on there until the thinset cures, if you want. But it needs to be flat and flush with adjoining boards while it cures.
      2. Yes.
      3. No, thinset does not cure because it’s exposed to air, it’s a chemical cure. It will cure at the bottom of a bucket of water. You need to pay attention to the working time of the thinset on the bag.
      3 (2). You need to clean the bucket first, especially with quickset.

  • Luz

    I am having tile installed in a bathroom and the hall way upstairs that when I took out the carpet has plywood, my contractor want to put the tile on the plywood, I Have read we need backer board but what happens to the toilet ,dose it have to be removed and reset on top of the tile?

    • Roger

      Hi Luz,

      Yes, it needs to be removed and tile is installed beneath it.

  • fred

    Just letting you know this article was one of the best ones I have read in helping with my project great job.

    Thanks,
    FRED

  • Daniel

    Hello,

    Is it okay to use the liquid floor leveler before setting down your backer board?

    • Roger

      Hi Daniel,

      No, because you can’t screw through it without cracking it. You can use the thinset that should be installed beneath the backer to level it out if you need to. If you want to use the slc just install the tile right to the cured slc – no need for backerboard at all.

  • Jerry

    Jerry

    Hi Roger
    I am tiling a floor with only 5/8″ plywood for the sub floor. I was planning on adding another 5/8″ plywood layer and then backer board or Schluter Ditra which is best for this job? We are using 12″by 24″ porcelain tile.

    Thanks

    • Roger

      Hi Jerry,

      I prefer ditra, but either will work fine properly installed.