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 cementious 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
You need to realize that cementious 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 - 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
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
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.
Each 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
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
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.
{ 16 comments… read them below or add one }
I want to replace my tile in my entry way. The old tile is set in a cement bed and I have been advised to tear up the cement bed and then build up the floor using a sleeper floor.
My question is about the sleeper floor. How sturdy is a sleeper floor…I mean it has space between my original subfloor and “new” higher floor. I am thinking that the tiles will crack over time.
The second question is how important is it to get the strips of wood parallel and attached to the floor joists on this sleeper floor? It seems that I would be redistributing the weight of my floor if the base of my sleeper floor is not over my floor joists correctly.
Thanks for any advice you can give me
Hi Will,
I’m unsure who advised you to build a sleeper floor to tile over but that is one of the worst solutions. You’re absolutely correct, depending on the quality of wood used, the height, as well as several other factors the amount of movement makes it unsuitable for tile installation.
Your best option is likely another mud bed. Just tear out what needs to be gone and mix up some deck mud (just like a shower floor) and create yourself a nice flat, solid substrate for your floor. It’s cheaper and better and a proven method – no way to lose.
Hi Mr Floor Elf:
Love your style & humorous writing.
I don’t have too much physical strength. I love working with my hands. I’ve previously vinyl tiled & grouted the side entrance & 2 flights of stairs & now I want to tile the front foyer. I want to use granite tiles 12×12.
(I think it’s backerboard. I found it in the basement & it is grey-cement looking with mesh.)
I hope you can advise me on my flooring dilemma. But please don’t get too technical. I’m a mom of three & I’m 5.5″ & weigh 100 lbs so please nothing difficult.
The floor is now stripped down to something that looks like planks. If i’d remove those planks-I’ll fall through into the basement. Here’s the problem. If I lay down 1/4″ backerboard & the granite tile on top, I can’t open the darn door!
Any ideas??
Hiya Goldy,
They look like planks because they are planks.
And it does sound like backerboard, but I can’t see it from here so I dunno.
The problem is that with a floor installation there needs to be a minimum of support below your tile. This is measured by what is called the ‘deflection ratio’ of your floor. In English that just means a number that measures how bouncy your floor is. The higher the number the less bouncy – get it? Now, for a normal ceramic or porcelain installation this number is 360 – a number I’m fairly certain was brought about by counting the number of unicorns in a particular smurf village. That part isn’t important, what is important is that for a natural stone (granite, for instance) this number needs to be double, or 720 unicorns.
To reach this magical number requires a minimum of 1 1/2″ of subfloor – that would be your planks plus 3/4″ plywood screwed to that, then your underlayment or tile substrate, then tile. It sounds like a lot because it is a lot. You need to make absolutely certain that your floor is not bouncy below your tile. If it is your grout will crack, your tile may crack, and my dog will burst into flames. My dog is tired of bursting into flames – so don’t do that.
Your deflection number does not necessarily derive from the layers of flooring but mostly from your joist structure. As long as your joists are in good shape and you have the required number of layers in the correct order you should be fine. I can check the specific deflection ratio for you if you would like but this would require numbers from you describing your joists sizes, spacing and unsupported span. (Real tile guys actually have to know math – weird, huh?)
Cementious backerboard (the gray stuff) does not positively affect this number at all – it is not made for, nor does it help, floor deflection. So, the bottom line: You need at least 3/4″ of plywood screwed to the planks (NOT into the joists), then your underlayment, then your tile. So above your planks you need about an additional 1 3/8″ of stuff.
Now, that will get your floor to the point of being properly installed and have it last – not too difficult labor-wise, but it does require the proper layers. It doesn’t solve your door problem though, does it? If you are able to cut the bottom of the door so it will clear all these layers you can add the proper height of layers to your threshold so it is still properly sealed at the bottom and you don’t get a nice, cool breeze blowing under the bottom of your door.
The only other option would be to remove the planks in that area and drop the joists low enough to allow for those layers. But that option is not really easy – at all. So I think cutting the door down to size to allow for the tile installation would be your best bet.
Just make sure you have enough unicorns.
Thanks for dumbing it down for me. Dropping the joists is exactly the kind of physical labor I can definitely NOT do.
Don’t roll your eyes too much, but the wood which I think looks like planks measures 3/4″. (Found a broken corner where I was able to stick in a ruler.) I’m trying to keep up with your math & all the unicorns. So do I still need a 3/4″ plywood, & then the 1/4″ backerboard? & here is another eye rolling question, how can I see the joists? The floor is completely covered with the planks & they are really tight & secure. Should I pull up the planks & see what’s doing underneath?
I’m not thrilled about the idea of cutting the bottom of the door & then raising the threshold. Too much detailed surgery. I’ll need a PHD first. The door is 60 something years old & I can see daylight at the sides. Thought about replacing the whole front door. If I leave the marble saddle in place & install the new prehung door on top of the existing marble saddle, I would get another 3/8″ for clearance. It may still not be enough.
Am I completely crazy?
Hey Goldy,
Even with 3/4″ planks you need 3/4″ plywood. You do not need to use the 1/4″ backerboard, you can use something like Ditra which is only about 1/8″ thick. The purpose of the underlayment is to have a substrate suitable to stick the tile to. Backerboard, Ditra, things like that. The thickness is not important.
You can either take a look at the joists from below or take off the planks to get a look at the joists if you want to. Not really necessary unless you want an actual deflection number.
If you are going to install a new door I would pull everything out including the threshold, install the 3/4″ layer of plywood, replace your threshold and place the new door on top of the saddle at that point. That should give you enough clearance for your underlayment and tile.
Your not completely crazy… Just enough to want to install tile.
Ok, so I’ve been mulling this over the last couple of days. I work very slowly when doing repairs. I work all day, then take care of the kiddos & only after everything is done, I can treat myself & indulge in redoing the house. Now if I do the tiles in stages, like plywood one day, backerboard another day & so on.
Problem is, if I take out the front door, I can’t leave the door off for a week. I need to get the new door up the same day. I don’t know if I can finish that fast.
So now I need to get a professional to install the door & only then can I continue with the tile.
You can always pull everything out up to the threshold one day, the next day pull out the door and threshold and place 3/4″ plywood beneath the threshold, replace the door, then continue as normal. If you can pull out the threshold, place plywood beneath where it goes, then replace it all in one day you’ll be fine. The only real issue you have is that the threshold isn’t high enough. If you can get that moved up before you start you’ll be fine.
The 3/4″ plywood beneath the threshold does not have to be tied into or a part of the actual 3/4″ of plywood beneath your tile in the entryway, it can be separate. The only purpose of placing it there is to give your door enough clearance. It does not necessarily need to be installed last. As long as you can get it moved up with enough clearance before you start that would work fine as well.
You are right.
And so I did a test run. I have some interior french doors that had warped jambs- got them at a steep discount. Of course, this was b/f I started studying & experimenting as a DIY’er & I did not realize the jambs were warped. Thanks for letting me ramble here.
I figured if I can get those doors hanging properly, I’ll trust my abilities & attempt installing a front door. Well, success! The doors are hanging almost perfectly. (Can doors ever be perfect?) The reveals are pretty straight & the doors open & close smoothly. 
It took me three days, but I’m happy
So I am going ahead with the front door. Still some hurdles to cross. I really need a better math education- don’t tell my kids. I must crunch the numbers to make sure I can raise the door up enough. Not sure if I have enough clearance up on top. And the door jamb widths on the exterior pre-hungs at home depot & lowes are only about 4 & something wide. My door opening is around 8″. I know I may have to do a jamb extender.
Slow & steady here. Slow & steady.
I have a question. I was told by a contractor that PL premium and 1 1/2″ ring nails would work for installing Cement Backerboard to the sub floor????
Hey Chad,
Sure, that’ll work as long as you are installing vinyl on the backerboard. That particular method is a favorite of handymen and people inexperienced with proper tile installation. They interpret placing thinset beneath the backerboard as a way to ‘stick’ the backerboard to the substrate. It is not.
Thinset is placed below backerboards only in order to fill any voids beneath it. Any type of glue such as the PL premium you are talking about will do the complete opposite – it will leave voids and create spaces. Rather than eliminating movement it actually creates it.
Get a bag of thinset and place that below your backerboard. And find a new contractor.
Roger -
great site and beautiful work….wish you did work in CT….
I am having a full basement bathroom installed and just wanted to ask a few questions regarding tile installation.
Half of the basement is already finished. So, we will be breaking through the wall that separates the finished from the unfinished side and adding a bathroom there.
My friend is a contractor who is doing the work.
Here is the tiling plan:
Floor:
2×4 sleepers, 16 o.c. (pressure treated) attached to concrete with PL construction adhesive and Red Tapcon screws (to get the bathroom level with current finished area)
(current finished area is also 2×4 sleepers, 3/4″ plywood and carpet)
Plywood subfloor (3/4″ tongue and groove underlayment)
Plywood screwed down into sleepers
1/4″ Hardiebacker set onto plywood with thinset
Screw down Hardibacker into plywood (BUT NOT into sleepers)
Thinset
Ceramic Tile
Shower:
Swanstone shower base (bulit up on same sleepers and plywood as rest of bathroom floor)
Quikcrete Sand topping mix under Swanstone base for support (as recommended by Swanstone)
Plastic/poly sheeting for moisture barrier attached to studs with staple gun
Durrock walls
Tape Durock wall seams with fibergalss mesh tape and smoothed with thinset
Thinset
Ceramic Tile
Now here is my dilemma.
I am reading that tiling over 2×4 sleepers on concrete is a bad idea…..the only real option is a mudjob…
Apparently, moisture/dampness in the voids created by the sleepers can cause movement in the 2×4 sleepers…thereby possibly causing cracked tiles/grout. True? Any remedies for this?
Shouldn’t the combo of Tapcon screws and PL glue hold the 2×4 sleepers in place to minimize any movement?
I will try to look into the mudjob….but I have to try to find a reputable guy in my area, plus I bet it is expensive due to the labor involved….
Overall, does the plan look good? Any criticisms or suggestions would be helpful…..
If more info is needed, please let me know and I wil provide.
Thanks for the help. I sincerely apologize for the long, segmented post…I just wanted to make sure you had all the info you needed.
mm
Hey Mike,
I have combined your comments into just the one. Apparently it is too long for a normal comment box, sorry about that.
The information you’ve found is correct – you do not want to tile over sleepers on concrete. Concrete will allow moisture to evaporate up through it from the ground and this will get trapped between the sleepers. Air and moisture with no way to escape is never good for tile. Tapcon screws and PL glue are not sufficient to hold those sleepers in place when you start injecting those two things into the equation. I know that doesn’t sound right – but it is true. Trust me on that.
It sounds as if you only have about 2 1/4″ from the concrete to the level of your floor outside this area. That is actually ideal for a regular mud bed for your floor. I really don’t know the price of labor in your area for mudwork but you can always ask around. Or, if it is an option, you or your contractor can do it yourself. A mud bed for a floor is actually fairly easy if you use the correct method and take your time. If you’ve read through my ‘how to create a shower floor’ threads it is almost just like that. Same mixing ratios, same techiniques, except you are making the floor flat rather than sloping it.
The price for materials is just about identical to using the sleepers, plywood, and Hardi. In fact, it will be a bit cheaper since you are only buying concrete and sand. When done carefully (take your time) this is the best way to achieve an absolutely flat floor for a tile installation. I would do it all the time if I had the space to bring the floor heights level – you already do.
You basically just mix up the deck mud, get your height level around the perimeter and place screeds at that height for the remainder of the floor. Fill in the center and screed it off level. The next day you have a perfectly flat, level floor for your tile. If this is an option I’ll be more than happy to answer any questions you have as you go along.
The only other option I can think of to raise your concrete to the level of your floor outside that area would be a membrane made to raise the floor in commercial applications. These would be varying heights and would probably be difficult to find one that would match the height you need. They are also extremely expensive. The price of the membrane would be more than hiring a professional to install a mud deck for you.
I would go the mud bed route. It enables an uncoupling barrier between your concrete and tile and gives you a worry-free substrate. Hope that helps. If you have any more questions please feel free to ask.
thanks for the info roger .. i think i will go kerdi drain and pre slope
hello roger thanks for all the info on you site .. i have a ? can you use kerdi on the shower floor with out using the kerdi drain ? if you can how ?
Hi Ed,
You can but, to be honest, its a pain in the ass.
What you need to contend with is the weep holes in the lower half of a regular clamping drain. In a traditional shower you will have from 3/4″ to 1 1/4″ of deck mud above the weep holes. To deal with this with the Kerdi membrane you can use what we call the ‘divot method’. While more commonly used with liquid membranes it can also be utilized with Kerdi.
What you do is create the shower floor but leave a large divot from the top of the mud bed down to the weep holes. When done correctly it looks like when you made your mud bed you left a volleyball sitting on top of your drain flange. It’s a regular bed then about 4 – 6 inches around your drain it dips down in a reverse sphere to your weep holes.
The pain part comes when waterproofing this particular part of the bed. Kerdi doesn’t like circles very much. While it is absolutely possible to do it’s a questionable process for someone not very experienced with Kerdi. To ensure your floor is waterproof in that spot, which happens to be the lowest spot in your shower and therefore sees more water than any other part, you need to have a rock-solid technique and absolute confidence in your ability to properly waterproof strange shapes with Kerdi. In other words it takes a lot of practice.
After doing that you just fill in the remainder of the divot with deck mud and tile as usual. the deck mud in the divot will become saturated and drain correctly just like a traditional mud bed but the remainder of your shower will be topically waterproofed – that is waterproofed directly behind your tile – with the Kerdi.
You must use this method because if you do not have your waterproofing below the weep holes the water will drain into the top of the drain and some will drain out of the weep holes. If the Kerdi is not below the weep holes that means it drains into your floor, framing, basement, kitchen, antique pez collection, etc. It is a very specific process and one I would be extremely leery recommending to someone without much experience. Not that you couldn’t do it, just that I would not recommend it. But hey, it’s your pez collection, do what you wanna.
Another mildly insane tile contractor from New Yawk named Gueuze (pronounced goose) has put together a ‘tutorial’ of sorts describing his method of waterproofing with liquid membranes. It does, however, explain the ‘divot’ with photos and everything. It can be found Here. (The first page is with the Kerdi drain, the divot photo and discussion starts on page 3)
Hope that helps.