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.
Hi Roger
I’m doing a small bath. I’ve layed down one layer of 3/4″ plywood over 16″ OC 8/4″X6″ floor joists. I was assuming that that would suffice before laying down my 1/2″ backer board. So, are you saying that I need to add another 3/8″ layer of plywood before I proceed with the backer board? Wow, looks like I was about to commit a grave error. Right?
Thanks, your a Godsend.
Patrick H.
Hey Patrick,
Yes, you should have another layer. A correct substrate consists of a double-layer plywood 1 1/8″ minimum thickness.
I have a new plywood sub-floor and will install Durarock on top of that. I am wondering if the the direction of the cement board should match the direction of the plywood. Does it matter? Should I avoid the alignment of plywood joints with cement board joints? (you mentioned not screwing into joists) Any help appreciated, thanks,
Matt
Hey Matt,
The direction of the backer should be against the grain ideally, but it isn’t a huge issue. The seams of the backer, however, should be offset from the plywood seams by at least 1/3 the length of the backer. In other words with a 5 foot backer you need to place it overlapping the seam by at least 1’9″. I try to overlap it by halves if possible, not always possible on larger floors.
Hello Roger,
After you install the pan liner on your pre slope, should you install the cbu’s on the walls before you put the top layer of deck mud? I am putting a niche in so I am just going to red quard all the cbu’s. I know that I can’t put screws through the cbu’s into the liner, so would the top layer of mud help hold them? Also, metal lath on the curb, before or after the deck mud. Thank you for your time.
Hey Scotty,
Yes, you can install the backer before the top deck – it will hold it in place. The lath goes on the curb before the deck mud.
Hi Roger,
I have a question about leveling a sub floor. I used 3/4″ plywood over the slat board sub floor. Some of the joints are slightly higher and there are some slight dips and high spots. Do you just sand down the high spots and let the thin set cover the low spots? I was considering using the leveling compound for the low spots, but after reading some of the other questions it sounds like you use the (SLC) after you have installed the backerboard and on top of primer. Is this correct and what type of primer do you use?
Hey Andrew,
It depends on how out of flat your floor is. You can sand down the high areas and fill the low if it’s less than 1/8″ or so. You can use slc directly over the plywood – no problem with that. Every slc has a dedicated primer for it, use it first.
Roger,
I plan to use thinset and 1/2″ hardibacker board as the substrate for a tile floor of a second-floor bathroom. I am also planning to use the laticrete paint-on waterproofing membrane over the backer board.
I would like to reduce the sound coming through the floor. Do you have any experience with sound proofing membranes? Do they actually reduce noise? The installation instructions for the membranes I’ve looked at show the membrane over the substrate, with tile installed directly over it;
however, most of them are installed on a wood or concrete subfloor.
Do you have any thoughts on this?
Thanks,
rebecca
I’ve done this before without the membrane, and the floor seems to be holding up well.
Hey Rebecca,
Yes, they do work. The best way I’ve found isn’t really a membrane – it’s a thinset. Laticrete 125 sound and crack adhesive works very well for both installing the tile and dampening sound.
Roger,
I have been reading websites and watching youtube videos, and I have to say your blog is by far the best I have seen. It is interesting, amusing, and informative. I have bookmarked it so my husband can use it as a reference for our upcoming tiling project. Thank you so much for taking the time and effort to post such a great explanation of the tile process!!!!
Hi Joy,
Thanks! I’ll be here when he’s ready. Speaking of which – what the hell is he waiting for? Tell him to get movin’! That shower isn’t gonna build itself…
Thanks Roger.
How thick should the top mud bed be? Also, when mixing mud for your curb and a shower bench, you said it is exactly the same mix as your mud bed with one part lime added? 1 bag (60lb) sand topping mix, 25-30lbs of sand, 1 bag of lime? when you say 1 part lime is that a whole bag of how many pounds? i assume that i need some regular mortar mix to lay the block and to help backfill. I have a bag of mortar mix/stucco from HD. Can it be used for curb, bench or just to hold the plastic down in my garage?? Don’t know if you can tile over the mortar/stucco mix or not. Thank you again for your time.
Hey Scotty,
The top mud bed should be a minimum of 3/4″. One part lime means the same amount as the cement, in the case you’ve described it would be 15lbs. of lime. If you add a whole 50lb bag of lime you’ll have a bucket with a rock in it.
You can use the stucco mix for the curb and bench – you can apply tile directly to it. Yes, regular thinset to build your bench and curb (with bricks and blocks).
Hi Roger,
Great stuff here! I have a question where I cannot find a topic: leveling (slc) a floor and using Durock. The manufacturer states you should not use ANY self leveler with their product (I was questioning whether it should be poured over the Advantech, then the thinset/rock or thinset/rock, then leveler). They said neither is acceptable. I have just under (7/16″) of a dip/belly over 15′ and I’d really like to correct it. I honestly only want to fix it because the tub is going there (6′ tub) and I’m making the skirt out of tile. The tile will be noticably running downhill (left to right), perhaps only to me, but it will bother me for the rest of my life and beyond. Any suggestions other than basically shimming the whole area? I’m not a carpenter, (plumber), but I’ve been around the trades long enough to get me in trouble.
Thanks Roger!
Doug
Screw the manufacturer!
(I just love saying that.)
I would thinset and screw down the backer then prime it and use the slc. I’ve done it several times and don’t have problems. I do, however, use ditra over that. But there’s no reason I can think of short of improper deflection (too bouncy) that will cause problems with that.
For what it’s worth (and it isn’t worth shit in my opinion) USG also does not require a moisture barrier behind their product and, in one instance, actually attempted to convince a customer that it was not necessary in her shower. All they are doing is trying to cover their ass with absolutely every scenario. Just be sure to use a primer under the slc and you’ll be fine.
Thanks for convincing me! I kept thinking about it, and why the hell couldn’t you use it over CEMENT board?? Thanks for your help and thanks for your tile tips (ebook I bought). Now……about said barrier….I work with many contractors and one said to use felt paper (instead of 4 mil plastic). What do you think of that?
PS I was hoping you wouldn’t mention Ditra ($). It’s my house, so I do want to do it correctly, but the new bathroom’s going to be about 100 sq’ ($$$$ for everything!). What material of tile do you most suggest for the flooring?
Thanks again for everything,
Doug
Roofing felt is actually a better moisture barrier than plastic. The pores of the paper swell when exposed to vapor and tighten up. Go with that – he’s correct.
Porcelain is going to be your most durable tile product, and easier to maintain than any of the others.
Hello Roger.
Great help for many people. Thank you for a trusted source of information. A question about my subfloor and underlayment. I am building a deck mud shower pan (rubber liner) with cbu walls with Redguard. Tiling the bathroom (very small) floor also. Floor Joists are 2X12, 16″ oc, with 1/2 plywood subfloor (built in 1975). I put a piece of 3/4″ plywood underlayment in the 3X4 shower stall. Would it be ok to put a 1/2″ plywood underlayment, with 1/4″ hardiboard for the bathroom floor? This bathroom runs parallel to an outside wall. I removed a 1/2″ particle board underlayment.
Also, would it be totally wrong to lay the underlayment the opposite direction of the subfloor? I know it would be running with the joists instead of across them, but would it matter in this 5×6 bathroom?
One more please. Screws or nails in the underlayment? if screws, which do you prefer? Thank you very much.
Hey Scotty,
1/2″ ply with 1/4″ backer is fine. The backer can go over the floor however you wish, makes no difference. The second layer of ply should run perpendicular (the opposite direction) as the first layer.
I use deck screws in the ply and the appropriate backer screws (hardibacker or durock) for the backerboard.
Hi and thanks for all the information…making my bathroom project seem do-able! Some questions I have about floor tiles in a bathroom with a shower, even with the cement board as a substrate should you use any kind of waterproofing? If tile and grout are not waterproof wouldn’t water dripping off someone’s body onto the floor eventually make it to the subfloor? My wife has a habit of getting water everywhere when she’s done in the shower and I’m concerned about where -eventually- that water ends up!
Hey Arne,
You can place a liquid topical membrane over your backer or a sheet membrane like ditra but there’s really no need for the waterproofing aspects. Short of a flood on the bathroom floor any water will evaporate faster than it will be absorbed and it would take quite a bit to even reach the backer beneath your floor tile. A lot of people like to waterproof in front of the shower for water that makes it out of the shower during use and that helps. You can do it if you want, it’ll definitely help, and either of those products have different benefits then waterproofing for floors – they also compensate for substrate movement. So it definitely won’t hurt anything – and it will help.
Hi Roger,
I’m tiling my conservatory over chip board, but will not be having under floor heating. Was thinking of using 10mm back boards, is this enough?
It seems pretty clear I should use thinset under the boards, but will I still need to thinset between the backboards?
Thanks!
Hey Brett,
The 10mm boards will be plenty. If you are speaking about taping and mudding the backerboard seams then yes, you still need to do that. The tile will be bonded to individual boards, you want them all to move together, not separately.
Excellent article Roger. Wish I would of read this before last weekend. I did put thinset though so dog will be fine. My concern is the screws I used initially for the backerboard-to-plywood went past the plywood floor (house is on cement piers) and I can see them when I peak under the house. Went to HD and got the right size to finish off the other half of the flloor. Think this will be a problem later (screws getting loser faster) cuz they are longer and exposed?
Keep up the good articles…….
Hey Rico,
No reason that would be a problem at all. Unless you have little sprites under your house pounding up on the bottom of the screws with a hammer.
And again……I am so sorry for double posting! I don’t know what my problem is!
Hey! Don’t worry about it. I see double every now and then too.
I know my Lowe’s has Laticrete, so we will use that. My Lowe’s only carries Ditra and we just can’t afford that right now. I hope the tile will be ok without it.
Going to Lowe’s to get all the stuff shortly. I hope this is my last question for you….but I can’t make any promises! :-)
1. What kind of thin set? I know Latricrete. But modified? Unmodified…acrylic..whatever….The tile guy with 15 years experience prefers white because it’s fluffier. Is this true? Our tile and grout will be dark brown.
And do I mix with just tap water?
2. 1/4″ trowel?
3. 3/32″ spacer for tile that is 6 x 20 is ok?
4. Sanded grout. Is there only sanded and unsanded grout? Special blends?
5. Anything else?
Sorry for sounding so dang uninformed. I really have read sooooo many opinions that I just want to make sure what I am getting is not a waste of money.
THANK YOU, AGAIN!!!!
Pauline
1. Modified thinset. White thinset is absolutely no different than the gray thinset. The color is the ONLY difference (and the price). If you have dark tile – use gray.
2. 1/4″ trowel is fine as long as your walls are flat. If you aren’t getting good coverage just use a larger trowel.
3. Whatever spacer your tile will allow. If you can use a 3/32″ and keep the grout lines straight then it’ll be fine (that should be no problem at all). It all depends on the tile.
4. There is also epoxy grout. Use sanded grout – preferably the Laticrete. If you want to use epoxy – use it. It is, however, more difficult to work with.
5. I’m sure there’s plenty else. Difficult to answer, though, without specifics.
Hi Roger—
Thank you for your website and all the information you already have given people. I do have a couple of questions, though.
I am planning to:
-tile kitchen floor with 6 x 20 wood look ceramic tiles using 3/32 spacers and dark grout to match the tile.
-over concrete slab (home was built in 1987).
Issues/Questions:
1. We removed the old original vinyl flooring. There is a 12″ x 12″ swath of black adhesive (cut back?) that is seriously fused to the concrete. It is creating a high spot (less than 1/8″). The people at Lowes and HD tell me to leave it alone due to asbestos issues. And it’s the only issue we have in the kitchen that is not flat…or even level.
Question 1: Can I just leave it and put a little less thin set over the high section and a little more in the surrounding area without compromising the integrity of the grout? If not, what should I do?
Question 2: Am I supposed to use a primer on the concrete with some type of an adhesive primer?
Question 3: Am I supposed to use an adhesive primer over the old cutback?
I have called Lowes and HD 3 times each, spoke with 6 different people and have had 6 different answers.
Question 4: The Lowes guy said I should use sanded grout (even with 3/32 spacer) because in his 15 years of tilling experience, the powdered just starts to fall apart. So, is it ok to use sanded grout?
Thank you for your help! I really need it. I honestly just want someone to tell me what to do! I’ll do it…I just don’t want to screw up the kitchen floor!
Pauline
Hi Pauline,
Have you tried soaking the cutback with water? Probably, but I always ask. That will often soften it up enough to scrape off.
1. Yes, you can flatten it out with thinset in the manner you describe – not as much thinset over that area.
2. No, if you are using thinset to bond tile right to the concrete (you should have a membrane, but not technically required) no primer required.
3. No, primer won’t do anything to the cutback. That crap’s like titanium.
4. Yes, you can use sanded grout. You can also use unsanded grout. The ‘powder’ (unsanded grout I’m assuming?) doesn’t ‘fall apart’ if properly mixed and installed.
4b. If he has 15 years experience installing tile professionally why is he working at Lowe’s for ten bucks an hour. Nevermind, hypothetical…
If your home was built in 1987 it is NOT asbestos. You can tell them they’re idiots. (Sorry, I’m in a pissy mood today
)
Hi Roger—
I am not sure if this questions went through the first time, but here it goes, again. And I am sorry if this is a duplicate!
Thank you for your website and all the information you already have given people. I do have a couple of questions, though.
I am planning to:
-tile kitchen floor with 6 x 20 wood look ceramic tiles using 3/32 spacers and dark grout to match the tile.
-over concrete slab (home was built in 1987).
Issues/Questions:
1. We removed the old original vinyl flooring. There is a 12″ x 12″ swath of black adhesive (cut back?) that is seriously fused to the concrete. It is creating a high spot (less than 1/8″). The people at Lowes and HD tell me to leave it alone due to asbestos issues. And it’s the only issue we have in the kitchen that is not flat…or even level.
Question 1: Can I just leave it and put a little less thin set over the high section and a little more in the surrounding area without compromising the integrity of the grout? If not, what should I do?
Question 2: Am I supposed to use a primer on the concrete with some type of an adhesive primer?
Question 3: Am I supposed to use an adhesive primer over the old cutback?
I have called Lowes and HD 3 times each, spoke with 6 different people and have had 6 different answers.
Question 4: The Lowes guy said I should use sanded grout (even with 3/32 spacer) because in his 15 years of tilling experience, the powdered just starts to fall apart. So, is it ok to use sanded grout?
Thank you for your help! I really need it. I honestly just want someone to tell me what to do! I’ll do it…I just don’t want to screw up the kitchen floor!
Pauline
Yup, right below (above now) where you typed this one.
Check your spam folder for your email notification. Email programs don’t like me – must be my charming personality. 
You mentioned a membrane, but not technically required. Should I put one in first? I am really needing to start tiling tomorrow (spring break is almost over).
Also, I can probably take a chisel and a hammer to that section of cut back…just was concerned about asbestos.
And…there are sooooooo many different brands and reviews of these products are all over the board, do you prefer a brand over another? For thin set, grout, etc?
Thanks!
Pauline
When I say a membrane I mean products such as ditra. It compensates for movement in your substrate (concrete) and dissipates it without transferring it through to the tile installation. It is not, however, required. Just a more solid installation. I believe lowe’s has what is called spidermat – same type of product.
I prefer laticrete products for, well, nearly everything. Thinset, grout, all that. However, being that your options may be limited the versabond from home depot is a good thinset. DO NOT USE polyblend grout sold by home depot – it’s a pain in the ass. Professionals even have problems with that stuff. Lowe’s nomrally carries Mapei products – ultraflex II is a good thinset from them and their grouts are good as well. If you’re lucky your lowes carries laticrete products – if that’s the case use it for everything.
Hey Roger,
As always, thanks for the impending advice! I am tiling my second floor bathroom, and will follow the step you mentioned here for the prep work…my question, should the thinset be modified or not between the subfloor and the hardiboard? And, would you reccomened placing ditra over the hardiboard prior to tiling?
Thanks,
Hi Steve,
It doesn’t matter which type of thinset you use beneath the backer – it doesn’t need to bond anything, it only needs to cure rock solid. It is only there to fill the voids beneath the backer. You can even use that $5/bag crap called ‘custom blend’ at HD, it’ll work fine. Just don’t use it above the backer anywhere.
I recommend ditra above the backer, but it is absolutely not necessary. I will be an added layer of protection for in-plane movement, but I realize it’s expensive. If you can do it, I would. It just makes your installation better. But the backer by itself is a very adequate substrate.
Great, thank you! I tend to completely overanalyze and build stuff far past the minimum…Im like you in that, if Im going to do it, its going to be right…the problem is, I dont know who to do it typically!! Thats where you come in, haha.
Another quick question, I will lay the ditra, I am installing a prefab shower pan (one of the swanstone color ones that I got for a ridiculous deal)…should I bring the Ditra under the pan and then place the pan on top of the Ditira? I suppose this would ensure water leakage would never get to the sub floor where the pan meets the floor tile, but, Im wondering if it would cause an issue with stability of the pan. Thoughts? Thanks!
…this was supposed to continue the thread directly below…I must have mis clicked.
It may cause problems, depends on your particular layout and structure. If you do not install it under the pan, though, it won’t cause any problems at all. I would just install the pan and the ditra up to it.
Great! Thank you very much!
So glad we googled you! We were about to lay Hardibacker without thinset (as instructed by the big box guy). Your directions were very detailed and easy to follow. We also enjoyed your sense of humor. We must have done everything as you “told” us to, because we now have our beautiful tile floor and our little Peanut did not burst into flames! He has, however, been condemned to the laundry room at night and when we leave the house since he is the reason we had to put up the carpet and install tile before we were ready to.
Hi Linda,
I’m glad you googled me too! Although I must say – it did tickle a little bit.
I’m glad I could help out.
i have two subfloors im taking two rooms and making one the first has wood subfloor the second has concrete slab i was thinking that i should backerboard the whole thing do you think i can screw down backerboards with cement screws this way ill have one big level floor
Hi Anthony,
You can, but it won’t last, so no. The best option is to use a flexible membrane like ditra or greenskin which you can bond to either plywood, concrete, or both. Attempting to attach backerboard to concrete always ends up badly and never lasts.
I have just removed the old tiles from the small washroom on the main floor. The tiles came up leaving the mesh & the old thin set.
My question; Do I remove the wire mesh and old cement or do I remove and start over with back board? The old mesh is showing in a few spots and was told at home depot that it could be patched with thin set. Also, it would add about 1/4″ to the height of the floor. The tiles were in good shape, just renovating and just replacing.
Your thoughts?
John
Hey John,
If the mesh is showing in spots it may be indicative of the entire substrate no longer being completely solid. While it can be patched with thinset – it shouldn’t be. The best thing to do would be to start over and build a proper substrate for your tile. However, if it is solid, and you have confidence in that, you can make some more deck mud and patch it with that. Adhere the new deck mud to the old with thinset.
Thanks Roger,
I think once I have everything removed (toilet & vanity) i’ll have a better feel for the old cement, but I am leaning towards removing eveything and installing new cement board, it would save me time/money and the headache in the end, if I had to redo the new tiles.
John
Roger,
I imagine you get asked this all the time, but is there a guide (faq?) for determining the correct trowel size for different tiles? I am also getting ready to do another floor and I would like to make sure I use the proper trowel for the hardibacker. Your assistance is appreciated.
Thanks, Dave
Hey Dave,
I don’t yet have that, but it’s a great idea! I may have to do that this weekend. I normally use a 5/16″ or 3/8″ trowel for most of my tile, but I have about 12 different sizes (no one needs that many trowels, I’m a tool whore
). For hardi to substrate I normally use a 1/4″ u-notch. If your subfloor is wavy a 5/16″ might be a better choice.
I just found your website. I LOVE it!! Now my question: I’m getting ready to tile a bathroom countertop. It is small (about 6-8 square feet), and I’m using 6″ porcelain tiles. I’m installing a 3/4″ plywood top with sink cut-out. The guy at Lowe’s told me to go with 1/4″ Hardibacker, although I thought 1/2″ might be better. So I have my sheet of 1/4″, but the Hardibacker screws are 1 1/4″ long. I don’t really want them sticking down below into the cabinet (I don’t really care if nobody sees them . . . it just doesn’t seem right to me). The guy at Lowe’s also told me I could use standard wood screws, but I just read that you say that is a no-no.
What do you recommend? I can take exchange any of this stuff if need be. I bought the Spectralock and Mapei Ultraflex mortar, as well as 1/16″ spacers.
I’ve never tiled before, and I want to make sure my first experience is a success, so any recommendations will be taken seriously. I believe in doing things right the first time so that there doesn’t have to be a second time. I just need to know what the right way is!
Thanks!
Tracy
Hey Tracy,
You’re correct – you don’t want those screws sticking down. They’ll scratch the crap out of you the first time you reach into that cabinet for something.
Regular wood screws will not countersink into the cement board – you need the cement board screws. If you look at them they have little teeth on the underside of the head which cut into the backer as you drive them in.
I would install an additional layer of 1/2″ ply or use 1/2″ backerboard. The backer won’t add any structural strength, but it will prevent the screws from sticking through.
Hi-
Great website, I bow down to you…
I have sexy new sistered floor joists covered with 22/32 span sheathing under my ancient house’s gutted 2nd floor bath. Seems very stable to me but one of your posts somewhere (can’t find it again sober) suggests I need more. I am planning to thinset down 1/4 hardie (could go 1/2) then suntouch mat, then a mosaic tile (pinwheel). Questions are:
1. Do i Need more plywood? aka Where is the substrate post for floors?
2. Assuming I have hardie board or similar thinset over level ply- do I need to use SLC over around my warming wires? Or can I just trowel on thinset and set tile?
Thanks!
Hey Harry,
The minimum you want is 1 1/8″, so you need another 1/2″ of ply over that. You can use 1/4″ hardi over that. The in-floor heating is going to cause a lot of temperature differences, expansion and contraction. You want to have a double layer of plywood beneath all that to compensate for the in-plane movement the floor will have. I think I described it here: Cement backerboard for floors. I don’t think I’ve yet gone into detail on that particular subject except in the comment sections.
You do not need slc, but it sure does make the tile installation a hell of a lot easier. It gives you a flat substrate to set your tile on. But yeah, you can just thinset and tile if you want.
Thanks- I can’t find the comment where you describe the double ply fastening technique you favor. Can you please give me a recap?
You want to install the second layer perpendicular to the first and overlap the seams by 1/3 (not 1/2). Begin your fasteners in the center of the board and work outwards. Leave 1/8″ gap between sheets and fill those with silicone to prevent getting thinset in them and maintaining the ability to expand and contract.
UDAMAN!
Hi Roger,
You have helped me in the past, and am eternlly grateful. My question today is regarding the install of cement board on the floor. We followed your instructions for installing the cement board up to the point of mudding and taping the joints. Is there a time period I have to wait for the mortar to dry (between the ply and cb), before I can mud and tape? I think you say that you mud and tape as you tile? If you do mud and tape as you tile, how do prevent lifting/scraping up the tape when you trowel the thinset? Hope this is not too confusing. Loooove your site!
Hey Sherry,
Nope, you can mud and tape it right away. When I do it as I tile I flat-trowel the tape down and comb the thinset along the length of the tape holding one end if need be. If you try to comb across the tape you’ll pull it up with the trowel.
Hi Roger,
Just wanted to say thanks. Your instruction has been invaluable. You know it’s not that we love the diy stuff, it’s just really difficult to find anyone that seems to know what they’re doing, not ruin/ damage other areas of the house, or charge a fortune. So it really means so much to have found your site and recieved the pro info with a sense of humor. You have totally instilled confidence for future projects. Thank you for giving up your personal time to help us .
How you connect hardwood floor and tiles , tiles will stick about 1/4″ to 1/2″ above.
Hey Lucjan,
You can use a marble or wooden threshold or a transition strip like Schluter.
Roger,
Thanks for the write up, you’ve answered many of my questions and gave me some great pointers. I am about to embark on a tile job for my kitchen and adjoining laundry room. We are using 18″ tile for both. I have three questions for you.
1. I’ve determined that 1/4″ Hardiebacker will work best due to clearance issues. We have a sliding back door and only have 3/4″ from the top of our current linoleum to the top of the slider track, so we have very limited height clearance. Will 1/4″ backer suffice for the floor? The joist are 2×12’s and I dont feel any play in the floor. The house was built in 1904 and remodeled in 1994. I haven’t yet determined the subfloor thickness because we dont have floor vents (propane heat) and I have yet to drill into the subfloor to determine the thickness. I understand this will play a huge role, but what thickness of subfloor is ok for 1/4″ backer. In a previous reply you mentioned 1 1/8″ subfloor, but was that for 1/2″ backer or both? The internet seems to give mixed opinions on 1/4″ vs 1/2″ backer.
2. Should I remove the linoleum? I’ve heard horror stories of folks trying to peel up old linoleum and not sure I want to join them. But i’ve also seen the opinions on this subject go 50/50. Some folks say to screw the linoleum down, clean it, rough it up, use the right thin set and place the backer over the linoleum. Others say to remove the linoleum and start fresh. Your thoughts?
3. Cutting 18″ tiles…..best saw or option out there? Within reason of course…
Thanks, LA
Hey Luc,
1. 1 1/8″ subfloor is under any size backer. You need the proper deflection (joist structure) and a double layer of plywood. Over that you can use any thickness of backer as long as you install thinset beneath it to fully support it.
2. If your linoleum is cushioned then it should be removed. If not you can go over it. I am in the camp that always starts with the base structure – always. It’s the only way to know it’s done correctly. If you do go over it you do not need to rough it up. The thinset is only there to fully support it – it doesn’t need to bond to anything.
3. DeWalt D-24000. I own two of ’em. It’ll cut 18’s diagonally.