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
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 - 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.
PS, sorry I forgot to mention that it had two layers of construction paper over the 1″x3″ top wood layer, and two layers of vinyl tile on top. Thank you, Greg
Hello Roger, I’m having the kitchen remodeled. The House was built in 1946, and it has floor joists, with a 1″x 6″ diagonal sub-floor, and 1″x 3″ tongue and groove perpendicularly spaced boards. I want to put down 1/4″ backer board to make it the right height to align with the bottom of the kitchen cabinets. I’m trying to save some space by putting vinyl tile over the backer board to give me the exact height I will need, or 3/8″ under where I will need to be in the future. If I paint the backer board with a certain type of paint, will the vinyl tile stick to the backer board better, and be reusable, and if I need to re-tile in the future with ceramic tile, will I need to have the backer board ripped out again? Roger, any suggestions will be much appreciated! Thank you very much, Greg
Hey Greg,
I honestly don’t know how well those vinyl tiles would stick to backerboard. I wouldn’t think very well, backer is extremely porous and meant to be used with a cementious product which will bond into the pores. The glue on the back of those is a surface glue. That isn’t a very good match at all. If it’s only temporary, I’d say probably six months to a year, you may get away with it. If longer than that I would just screw down 1/4″ plywood. That can simply be unscrewed when you’re ready to change it.
If you do go the backerboard route with plans on tiling later on down the road you do need to put thinset under the backer. I just don’t know how much that glue or the glue residue would mess with the thinset bond after those tiles are removed.
Hi Roger. I am replacing carpeting with tile. I have 3/4″ chipped board on top of 2×12 joists that are 16 o.c. My questions are, can I use 1/4″ plywood on top of the 3/4″ subfloor then thinset, 1/2″ durorock, mortar, then the tile? can you estimate how much heighth the thin set and mortar adds. I am concerned with the heighth since it is abutting existing tile in another room and do not want a tripping hazard. I will have 1/4″ for the thinset under the durorock and mortar under the tile to match smoothly with the tile in the other room.
Hey Dan,
No, but you can use 1/2″ plywood and 1/4″ backer with thinset beneath it. That would add about 7/8″ – 1″ onto your subfloor before tile. The plywood has dimensional stability (vertical stress), the backer has zero. 1/4″ plywood stability is nearly zero as well – just not enough layers in it.
Roger, I know this subject has already been covered in various forms, as to the thickness of the sub flooring, but I’m facing a height differential problem. I’m planning on doing ceramic tile in the Master Bath, and hardwood flooring in the Master Bedroom. Right now I have 3/4″ fir plywood over 2″x10″ joists, 16″O.C. If the subfloor doesn’t have any give, as determined by placing a glass of water on the floor, and watching for ripples in the glass as you walk over it, do you think I’m safe to add just a 1/4″ layer of cement board over the plywood, using thinset in between. If I add an additional 3/4″ to the bathroom floor I’m looking at a 1/2″ to 5/8″ higher floor than the bedroom. The hardwood will be 3/8″. Thanks in advance.
P.S. If going with the 1 1/4″ floor is your suggestion do you have any ideas how to transfer from the two different floor heights without it being a stumbling hazard?
Hey Mike,
I wouldn’t do the 1/4″ backer over only 3/4″ ply. You really need at least 1/2″ ply over the bath area before the backer. There are several different options for your threshold transition, but you will have a height difference, no way around it with a properly built floor. The only real option beyond that is ditra xl can go directly over 3/4″ or you can install 1/2″ over the whole area – bedroom and bath.
Roger (this is the other Mike B), my understanding from reading the Ditra XL literature is: for natural stone, you would STILL need 2 layers (1.25″ total floor) and that you can use the Ditra over 3/4″ only if the tiles are ceramic or porcelain. I was worried about height differences as well, but with travertine, 3/4″ + Ditra is not enough, right?
Hey (other) Mike B.
Yes, that’s correct. With natural stone you still need the double layer with ditra xl. I’d forgotten about that requirement, sorry about that.
Great site and thanks for taking the time to answer our questions! I am installing 18×18″ travertine tile for a kitchen floor that has a U-shaped outline with an island in the middle. The subfloor is 3/4″ exterior plywood on 3″x11″ joists. There used to be a hardwood floor which I pulled out. I would really prefer to just place a 1/4″ concrete board and NOT add another 1/2″ ply over the top first (as is recommended) before proceeding so the new tiles are level with the adjacent floor. I know it is not standard to leave that 1/2″ layer out, but in your experience, how likely will I experience a long-term failure without it? Is it certain failure or one of those things that would be very unlikely to actually cause a problem in most cases? The house was built in 2008, so the subfloor, joists and foundation are like new and rock solid.
I just now noticed your response to Matt and feel silly for not noticing it before posting. Sorry for the duplicate question! The only thing different in my question is that my joists are pretty beefy and the construction is new. I was hoping you would say it should be OK without the 1/2″ layer, but I am guessing the answer will still be ‘no’.
Hey Mike,
Yeah, you need that second layer, especially with travertine, a fairly fragile stone. I can’t guarantee a failure, all I can do is give you methods that will guarantee success. The additional 1/2″ layer is one of those.
OK, I am now putting in the 1/2″ plywood. But just one last question: is putting deck screws every 8in or so along the edges and in the center enough to hold down the second 1/2″ plywood over the 3/4″ base? Do I need to put down an adhesive first like liquid nails or something similar or are screws enough to hold the two plywoods together adequately? I hope so…because if you saw ‘no’, I will have to pull up the boards and start over! But I want to do this right…
Hey Mike,
Screws are more than enough. You don’t need adhesive. You’re fine.
Thank you so much for your time and expertise – I really appreciate it. BUT…my stupidity and inexperience has caused the saga to continue. After 5 hours of hard labor installing the 1/2″ plywood, I sat there all proud of myself looking at the floor and drinking my beer, when all of a sudden I noticed the APA rating stamped on the plywood. Yes, of course it now turns out that I failed to install exterior grade plywood and instead used “CD” 5-ply Rough, Exposure 1 plywood. About half the floor is covered with the “C” side up and the other half with “D” side up. So how bad did I screw this up? Can this still fly or is this a re-do? Yikes! I am hoping since it is “Exposure 1”, it should be good enough? Sorry for all the questions today. I wish I could ship you some beers as payment!! http://floorelf.com/wp-includes/images/smilies/icon_whistle.gif
If you’re using backerboard over the ply it’ll be fine.
This is a great site. Thank you.
I have a 3/4 inch plywood subfloor. Can I use 1/4 inch backer board or do I have to use 1/2 backer board. I don’t want the tiles/grout to crack, but I don’t want to raise the floor a lot either.
Thank you for the advice.
Matt
Hi Matt,
If you don’t want the tile to crack you need to raise the floor. That’s it, no shortcuts.
That said, the amount by which it needs to be raised is inversely proportionate (normally) to the amount of money you spend for your substrate. The cheapest and highest is adding a 1/2″ layer of plywood, then thinset and 1/4″ backer. The lowest proper option is ditra XL over the 3/4″. It will prevent cracking, provide uncoupling and only raise your substrate ~1/4″ as opposed to the 3/4+ with the other option.
1/4″ backer, or even 1/2″ backer over just 3/4″ ply has a high probability of cracks in your grout.
LOVE this website. I swear I read through all the questions so as to not bother you unnecessarily (okay, so I scanned the last 50 or so), but didn’t find my question. Which is:
I am remodeling a small house –gutted, put down 3/4″ Advantech new subfloor over 2×10 joists on 16″ centers. It already feels super sturdy with no movement. Tiling bathrooms; Can I just use 1/2″ backerboard without adding anything else? And do I have to use the thinset layer under the backer, or can I just screw it down, use thinset over backer/under tile?
Hi Charlene,
If you are setting ceramic or porcelain tiles you’ll probably be fine with just the backer. If you are setting any type of natural stone you NEED the second layer of plywood under the backer. You absolutely need to install thinset beneath your backerboard.
Our kitchen floor cracks in some spots, and since we are redoing the cabinets we’re going to put in a tile floor. Would we remove all the plywood up to the diagonal floor boards? Then lay plywood, thinset,backerboard, thinset, tiles? Or can we like Mike is going to do, just put plywood over top of the existing layer and screw it down every 8 inches?
Thank you
Hey Whitney,
Depending on what shape the plywood is in you may just be able to screw it down well. If the plywood has thinset stuck all over the face of it I would take it out. Above the second layer, whichever way you go, would be thinset, backer, thinset, tile.
Thank you!
I installed a new floor and did not use the thinset layer… now my dog caught on fire.. WTF do I do ?
Hi Ed,
Put your dog out.
Don’t understand what you mean by not using the thinset layer, do you mean the thinset beneath the backerboard? If so there’s not anything you can do about it at this point short of tearing it all out and redoing it. Whether it lasts or not is pretty much a toss-up, depends on the floor beneath it.
Roger, I am putting backerboard on my bathroom floor and have just put the thinset and board down. Do I wait 24 hours for for the thinset to dry before putting in the screws. My instruction book is telling not to step on it for 24 hours but does not tell when to put the screws in. Thanks, Ginny
Hi Ginny,
Put the screws in right away. What instruction book would that be? No reason to wait unless you have an extremely wavy floor and you’re using the thinset beneath the backer to level it out some.
My husband and I will be laying a tile floor in the bathroom. We have 3/4″ ply. I think the proper layers are 1/2″ ply (screwed to 3/4″ply), thinset, 1/4″ backerboard, thinset, tile. Do I need to use Schluter Ditra in there somewhere? I am confused when to use Ditra? Is Ditra only when you need a waterproof layer? I am really concerned about my dog catching on fire!! I have plenty of beer on hand!!
Hi Kathi,
No, you don’t need ditra in there anywhere. Ditra, when used, is used in place of the backerboard. Backerboard and ditra are products that accomplish the same thing – give you a proper bonding surface for your tile. Ditra is a better option because you get added benefits such as vapor dissipation, extended in-plane lateral movement, etc. But it’s not needed if you are using backerboard.
Your just fine – have a beer!
Hi Roger, followed your instructions and got to this part “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”. So did just that taped over the spaces and put thinset over it. When I read the instructions for spacing on the wall with cement board it seems to suggest you fill in the space with thinset first and then tape over it. Now getting confused, is it different for the floor than for the wall? If you put thinset in between the spaces then doesnt that defeat the purpose of allowing things to “move”? Great site btw
Hey Alex,
The movement aspect of any installation needs to be around the perimeter or through the soft joints. It is no different on walls and floors, except on walls you normally have a change of plane in your installation. Locking the separate boards together allows the entire installation to expand and contract as one, provided there are perimeter joints. You can fill the seam before you tape it on the floor as well, makes no difference. The reason I did that is that on a floor the thinset will get into the seam fairly uniformly, on a wall it won’t. Filling it first on a wall ensures you get good contact.
Thanks again for the help. Moving forward with the bathroom job, and have a question. Do you have a view as to which, if any, of the tile saws available at lowes or hd would be suitable for DIY use? I don’t mind paying for quality, but don’t need something that wil stand up to professional use/workload. Outside of the current task I have been assigned, er volunteered for, (floor, tub surround), I don’t have a specific future use in mind. Would rental be a better way to go? BTW, I tried to find this answer on your site. If I missed it, sorry. Thanks!
Another question (sorry to bouther you) – I will be using various Laticrete products on my project, and called them to check on a couple of items. The tech guy I spoke with said that Laticrete products were not rated to be used with Ditra, so he could not provide me any adivce on that issue. So, I’ll ask you -is the 253 Gold thinset I am planning to use for my wall tile instalation also suitable for the the layer between the plywood and the Ditra? If it is, would I then use 317 (which I understand to be their unmodifided thinset) for the layer between the Ditra and the tile? If 253 is not suitable, what products should I use?
Thanks!
From a fellow DIY’er. I’ve found, for the several home projects I’ve done (kitchen floor, backsplash, hearth, bathroom), an inexpensive ($60/100) saw with a four inch diamond blade works fine. Granted the job will take longer and more so with a lot of cuts, but I’ve had the thing for almost 10 years and it does not take up much space in my tool shelf. Watch those fingers.
Hey Brad,
Both of the products you’ve referenced are suitable for the applications you’ve mentioned. 253 under ditra, 317 over.
Thanks!
Hey Brad,
The ridgid 10″ (WTS2000L ) is about the only one that will hold up to regular professional-grade use. Some guys like ’em, some don’t, but it’ll do the job. The R4020 7″ is a good portable saw, but I wouldn’t use it with a heavy workload.
Roger – Doing some planning on the wall portion of the project, and just spent some time reading your instructions on building corner shelves. Thanks for that. Question – I’ll be doing a brick pattern with rectangular tiles. When I get to the corner and am switching from the back wall to the side wall, do I match short tiles to short tiles, or do I match short to long? Said differently, do short tiles meet short tiles in the corner, or do short tiles meet long? (Seems like short to short and long to long makes sense.)
Hi Brad,
The better look, and commonly accepted method, is short tiles to long tiles.
Thanks. Will do it that way.
Question – Tiles are going floor to ceiling. For the joint where cement board meets dry wall ceiling, do you recommend alkali-resistant mesh (the same thing that I will be using for seams in the cement boad, that is) or something else?
Yes, alkali resistant mesh tape there as well. Anywhere it will come into contact with thinset.
Hi there! Finishing up the prep work on the wall and floor, and have a question: I am installing/replacing a skirted tub and understand that I meed to leave a space betten the bottom of the CBU and top of the tile flange. I’m wondering about running a bead of caulk in this space. Any reason(s) why this would be a good or bad idea. (I will be painting/applyin Hydroban to the CBU (Hardibacker) prior to tiling.)
Like Jeopardy, should have been in the form of a question “Any reason(s) why this would be a good or bad idea?”
Yes. Same answer.
Hey Brad,
You can leave a 1/16″ space above the flange or shim the backer out so it goes over the flange. You can silicone that space since you are using a topical membrane. In fact – you need to, otherwise it won’t be waterproof.
Roger – Thanks for your prior advice. Project is going well, if a little slowly. Beer runs are taking more time than I had planned. Dog is still flame-free. Question – As previously mentioned, I am tiling a tub surround in a brick pattern. There is one course of glass higlight tiles about 4 inches tall/high. When I set the first course of base tiles above/after the course of higlight tiles, do I set that course on the same pattern/offset as the last course of base tiles below/before the highlight course, or do I set it on the opposite pattern/offset? That is, do the courses of base tile on either side of the highlight course have the same pattern, or do the yave the opposite pattern (as though the higlight course was not there)?
Hey Brad,
I think it looks better, and proper, to have the pattern offset from the one below your insert or liner.
Dog is flame-free and beer runs taking up a large chunk of project time? YOU’RE DOING IT RIGHT!
I have a kitchen floor with 3/4 in floor boards diagonal across the floor joist with 1/4 plywood on top and covered with vinyl stick down tiles. I would like to know can I lay 1/4 plywood on top of the floor and screw it down every 8 ” to give a clean base to prepare for a new tile floor. After this I would put a scratch coat over mesh. Will the floor be ok to put the plywood over the original floor surface.it will give me a total of 1 1/4 of wood thickness.
Thanks
Hey Mike,
Provided it is 1/4″ plywood and not luan it should be fine. Unless you put a scratch coat over mesh.
DO NOT (!!!!!!!!!!!!!!!!) put a scratch coat over mesh wire beneath your tile! It is called a ‘Jersey mud job’ and it is absolute shit. And it WILL fail.
But yeah, you can put a 1/4″ layer of ply over that.
Roger,
I have a small bathroom in the upstairs of my house. Currently I have everything down to the original 5/8 plywood, and the joists are 2″ X 9″ with 12″ spacing. Floor size is roughly 7′ X 5′ and it feels very solid. I was thinking of putting down 1/4″ backerboard as I dont want to go any higher than this. I will also use a thinset between the 5/8 plywood and backerboard of course.
Thanks in advance,
Hey Kevin,
Is there a question there? For a proper substrate you need a minimum of 1 1/4″ double layer of plywood beneath your backer. I’m not saying it will fail, I’ve done plenty of single layer floors. Just letting you know what you need for a floor that conforms to standards. It will likely be fine provided it’s good and solid.
Hi,
I’m doing a bathroom remodel on a 1950’s house. I removed everything down to the studs and floor joists, as some of the plywood was bouncy and flaking apart. I’m going to install 12×12 ceramic tile on all the walls and floor.
Can you kindly tell me the layers of material to use from the joists up? Do I need plywood, or can I just install backboard directly to the joists. If so how thick on the plywood and backerboard. Should I lay down a plastic vapor barrier anywhere? On the walls, can I just screw backerboard to the studs? Thanks for your assistance!
Hey GT,
For the floor you need a double layer of plywood totaling 1 1/4″. Normally a 3/4″ layer and a 1/2″ layer. Above that you need thinset then your backer. Either 1/4″ or 1/2″ backer will be fine. On the walls you can screw the backer directly to the studs, but you need a waterproofing layer in there somewhere, either behind the backer over the studs or on the face of the backer.
Cool site – funny and informative. I am doing a bathroom remodel (reasonably handy DIYer), and have a floor question. The old floor is ceramic tile in what I would call a traditional thickset – tar paper, metal lathe 1 1/2 inch mortar, ceramic tile. The ceramic tile is in perfect shape, i.e. no cracks, loose or displaced tiles, etc., but needs to be removed. The subfloor is 1/2 plywood over 2x10s 16oc, with about a 15 foot span. The question I have is what do I need to do to prepare the floor (once the old floor is removed down to the plywood, that is) for new ceramic tile. Do I need to re-do the thickset, or is there a different way to go? On one hand, re-doing the thickset seems to involve a lot of mortart. On the other, I want to make sure the floor is sufficiently stable. Any advice would be most appreciated.
Hey Brad,
You can do another mud floor with deck mud if you want. If you have it down to the 1/2″ ply you can also install a second layer of 3/4″ ply, then your tile substrate and tile. Once you have it down to the initial layer you can do it however you want. The deflection is adequate for any type of substrate you choose.
Thanks for the reply. Really appreciated. To make sure I have it right, I can add 3/4 plywood, 1/4 CBU and tile?
Thanks again!
Brad
Yes, as long as you have thinset beneath the 1/4″ backer.
Yes, got that – thinset beneath the backer board. One more question, if you don’t mind:
I see where you really like ditra. For the job I have described here, would you recommend I use it? If so, could you describe the “build up”, ie new plywood, thinset (modified, unmodified), ditra, thinset, tile?
In addition to the question re Ditra, above, a couple of other questions came to mind late last night (when I should have been either sleeping or having a beer, not worrying about a bathroom renovation).
When fastening the new 3/4 ply over the existing 1/2 ply, I understand that I should use deck screws, and not into the joists – only the old plywood. Is that correct? Separately, should construction adhesive be applied between the sheets of ply?
Thanks so much! Your advice/time is very much appreicated!
Yes, Ditra is always a better option. If you use it you want the second layer of ply then modified thinset, ditra, unmodified thinset, then tile.
Correct, only into the first plywood layer. No construction adhesive, it may create voids.
Thanks!
Your site is great…a smart ass who know his stuff. Anyway, I have been doing a ton of research and of course everyone says different things. I ripped up the vinyl floor. I will then put down a thin layer of thin set and place the cement board down. I will then screw them down. This is my question. I have heard before you want to screw them into the joists, but you mentioned not to? I am also going to lay the tape where the cement boards meet when I lay the actual tile. How long do I have to wait until I start laying tile after I attach the cement board?
Hey Chris,
TCA specs state NOT to fasten the second layer of ply to the joists, only to the first layer of ply. You can begin to set tile as soon as you have it screwed down.
Hi,
I want to know if I can use 1/4 0r 1/2 cement board or fiber board on my old kitchen Floor. The floor has a layer of vinyl tile on 1/4 popular underlayment which is on top of 1/6 x 5/8 or 3/4 thick floor board cross diagonal over the floor joist.Will I be able to use modified laytex cement between the new boards you recommend and the vinly tiles.After that screw it down over the old vinyl floors.
Thanks
look forward to your reply
Hey Mike,
The 1/8″ ‘popular’ underlayment is likely luan and needs to be removed. If you want a proper substrate that needs to be removed and a 1/2″ layer of plywood installed over the bottom substrate. Then any of the cement boards you’ve mentioned can be used with thinset beneath them. Luan beneath any tile installation causes problems.
I have built a 17×20 screened porch off the back of my house. I am looking to use 18″ floor tiles. The bottom plate on the walls is a 2×4 laid on the side. The floor is currently Advantech. I am going to put down 1/2″ cement board on thinset. My concern is what can I do to prevent water from penetrating between the bottom plate and the cement board/tile. Everyone tells me to caulk it after I finish the floor where the tiled floor comes into contact with the bottom plate. Any other suggestions or will this be ok? I am proud of this accomplishment
and want it to last! Thanks for the advice!
Hey Greg,
Get some roofing felt (tar paper) and fold it down into that corner so it turns up the wall over the bottom plate about two inches. Install your thinset and backer and screw it down. You can then either cut it of flush with the top of the backer or go ahead and tile then cut it off flush with the top of the tile.
I’m laying tile in a bathroom in my new house that used to have carpet (gross, I know). I’ve pulled up the carpet, padding, and tack strips, and I’m noticing that the plywood in the room is multiple pieces (which I assume is normal) and not entirely level between a couple of the pieces. It is about a 1/16″ lip between the two pieces. Is it OK to just put my backerboard over that and progress with my project?
Also, should I ensure my thinset between my backerboard and plywood fills any gaps between the plywood?
Hey Wes,
It is fairly normal under carpet. As long as you get good coverage under your backer you’ll be able to level that out just fine. Thinset should not fill the gaps in the plywood, they are needed for expansion. Don’t pack them full.
Thanks for the response (that was fast!). I have done everything up to and including laying my backerboard on my thin set base. While it is more level than it was before, I can still feel a very slight lip when I run my hand over it. In my efforts to measure it I’ve come up with right around 1/16 of an inch. I don’t know much about this stuff, but my intuition tells me that is not good. What do you think?
If it’s only 1/16″ or so you can make up for that easily as you set your tile. The amount of thinset beneath the tile allows you to adjust it as needed.
Roger,
I’m remodeling a small half bath (about 5’x5′) in an older home. I’ve ripped it down to the studs and subfloor. The floor joists are 2″x10″s 16″ oc, covered by 1″x6″s laid on a diagonal. I need to make up 3/4″ BEFORE adding my finish surface. Am I better off to use 1/4″ plywood covered by 1/2″ backer board; or 1/4″ backer board covered by 1/2″ backer board; or some other combination? The other option I thought of is to rip up the 1″x6″ subfloor and replace it with 5/4 deck boards.
Hey David,
I would go with 1/2″ plywood with 1/4″ backerboard. As long as you install thinset beneath the backerboard it doesn’t make any difference how thick it is for an application such as that.
Hello,
Love your website and knowledge (and sense of humor).
I nailed furring strips to the studs to 3/4″. The Hardybacker screw is to short to penetrate the backer and the furring strip and still solidly anchor in the stud. Can I use just a regular screw. Or do I have to worry about the chemicals in the cement corroding the screw?
Hey Oliver,
You can use deck screws but they’ll be difficult to countersink. You can also use the coated screws made for wet areas (usually gray or green) but you’ll have the same problem with those. If you use a larger trowel to go over the heads of the screws you’ll be fine.
No need to post a question both here and my facebook page – I answer them all.
Thank you Roger,
)
Really apprechiate your quick response. (I will not send you this via FB
Floor Elf
I’m doing a small (7×10) bathroom floor.
Two questions: 1) Is it necessary to dampen the plywood or backerboard before stickin it into the bed of thinset. And 2) can I use 1 1/4 roofing nails instead of the $$$$ backer screws?
1. Nope, it’s only there to support the backer, it doesn’t need to bond to anything.
2. Yes, that is an approved fastening method. I don’t like it – but you can do it.
Roger,
I’m remodeling/increasing the size of my bathroom. There is currently a 3’x5’x2″ tiled mortar bed and an 3’x5’x3/4″ plywood subfloor under a fiberglass shower enclosure. Here is my plan: I’m going to rip the tile and shower out leaving the mortar bed and exposed subfloor. Then, I want to fill in the 3/4″ subfloor with the appropriate thickness of cement backer board (ensuring thinset is used between the subfloor and backer.) Next, I was thinking of covering the lot with self-leveling concrete to create an acceptably level surface before applying the tile. Do you think this will work?
Hey Rick,
Yes, it’ll work fine. Be sure to use the primer for the slc, it makes a huge difference.