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.
I am getting ready to lay cement board for my bathroom floor. I have 1/4 inch cementboard going over 5/8 tongue and groove. I have some “Mapie Kerabond”, not sure if you have ever used it before. Just wondering if that was ok to use under the cementboard or if I should go get some modified thinset instead, and wich one , modified or unmodified, to use for seams and to set the tiles?
Also the seams on the floor it sounds like you dont mud them, then tape, then mud again like on a wall? You just tape it and mud it? Thanks
Yes, you can use the kerabond under the backer. You do need to fill the gaps in the floor before you tape over them, then mud again just like the wall. Use a good modified thinset for your tile. If Mapei is readily available ultraflex II is a very good thinset.
does it matter what side a durock cement board goes on on a floor? because my dad is wondering.
Hi Amanda,
Makes no difference at all.
Roger, We have two layers of 1/2″ plywood (underlayment?, subfloor?) on top of floor joist. I pulled up the linoleum type sheet flooring in our 25 sq. ft. bathroom and removed what looked like potting soil from around the perpetually sweating toilet, then replaced sections of the rotted plywood. I bought 1/4″ HardieBacker from the Home Depot on top of which I hope to install 1/4″ ceramic tile (i.e., floor joists + 2 layers of 1/2″ plywood + 1/4″ HardieBacker + 1/4″ ceramic tile). I am wondering if I should use 1/2″ HardieBacker instead of 1/4″? Is 1″ (total) plywood thickness inadequate? I sill have my receipt from Home Depot. What is your recommendation?
Thanks so much for the great website.
Brian
Hey Brian,
Normally you need 1 1/8″ total, but you already knew that.
Being a small bathroom and you are installing thin ceramic tile as well as backerboard you should be fine with the 1/4″. 1/2″ backer isn’t going to add any more deflection ratio to your floor than 1/4″ – weird huh? 
True though.
New here, and need some help….thanks in advance. I am doing this remod job myself and so far have ripped out the particle board and the ply subfloor in the master bath and replaced with 3/4 subfloor ply and 1/2 underlayment ply.NThere was water damage around the fiberglass shower stall. Now I am installing the 1/4 inch wonderboard…if I don’t “snug” the wonderboard up to the shower and up to the tub there will be a gap….how do I prevent water from working its way down between them? can I caulk the plywood to the shower and tub? and then after tiling caulk again (kind of a belt AND suspenders approach).
Also, the jetted tub (old but I am keeping it) had a 1 1/2 inch gap between it and the wall along the long side (windows on the “head” side and faucet at the foot) Originally, this tub surround was roughhewn cedar planks….it is now drywall (greenbord). Here’s the question, I’d like to fill in that gap and have the tile come up to the edge of the tub. What is the best most correct way to do this? I thought I’d build out that wall by putting
1//2 inch grid onto which I would put 1/2 wonderbord, then tile and silicone the connection. does this sound do-able?
Thanks again,
Karin
Hi Karin,
Yes, you can silicone between the tub and ply and silicone again after tile. You can bump out that wall but keep in mind that if that wall extends beyond the tub deck you will need to figure out some type of transition for the edge.
Transition for the edge? I thought I would “rest” the tile on the edge and silicone…no good?
If you are building out the part of the wall over the sides of the tub which meet the other walls (normally a flush transition) then the areas where you built them out will stick out from the wall – you’ll need to do something with those.
Or am I misunderstanding and you are only building out the back wall?
Or am I just still drunk from last month?
hmmmm, ok, so the wall with the faucet already comes over the tub edge, the wall I want to build out is just on one side, the “head of the tub” is on a window wall. Maybe I should build it out so that after the tile is installed it comes up and butts the tub side??? currently there is a 1.5 inch distance and the “groove” is about 2 inches deepl This tub was designed to “rest” on a platform. It sounds like I may have to live with that groove along the side (a real pain to keep clean). As far as I know water has never gotten in there, but then again the tub is rarely used, although I’d like to make it waterproof just in case. Any ideas?
Thanks so much for your time…I really appreciate it!
Karin
oh right…only building out the back wall
Oh, nevermind then – I’m just rambling.
Thank you, Roger. I feel much more confident about this now. And my 2 dogs are Waaayyy less anxious too! by the way, which would you favor….bringing the tile over the tub edge and caulking…or butting it up TO the edge and caulking?
Thank you thank you….your site is the BEST resource I’ve found; I can’t imagine how you find the time to answer everyone but I surely do appreciate it. One other question….regarding verticle applications, I purchased the 1/2 ” cement wonderboard for the wall around the tub, but after using same product on the floor I don’t think I can get a clean corner on the vertical (this stuff just crumbles in the corners and on the cut edges). Is there a better product and perhaps not quite as heavy which will perform the same functions as the cement board? I am doing this alone….will I need help? Is there a “cheat” I can do which will enable me to do this alone? The muscle in my right arm is getting bigger than my left arm…any ideas on that as well. ok so a few more questions…but all on the same theme !
Hi Karin,
It sounds like your using durock – try hardibacker, you can get a much cleaner edge on it. If the weight is an issue you may want to use a faced substrate such as denshield. It’s a lot like drywall except it’s waterproof on the face of it.
I would bring the tiles over the edge.
Hardibacker it is! I shopped all over our city for Denshield and although the manufacturer says Lowe’s carries it; they don’t (unless I want to order a whole truck load of it). Too bad for me cuz it sounds perfect for what I want to do. Tile over the edge is what I’ll do. Once again, thanks for all your help. It is much appreciated!
Karin from Portland Oregon
hey roger ,chris again m8, floor is ready for tile curious what size trowel do u recomend for 12 by 12 marbel 3/8 thick would like to minimize hieght if possible thx have a great day
Hey Chris,
I’ll usually use a 3/8″ x 3/8″ (10mm) trowel for 12 x 12. That will give you plenty of coverage provided your substrate is flat.
Thank you for your column. I have a client who had ceramic tile installed in their kitchen, not particularly well. It cracked. They had it taken up and installed again. It cracked again. They realized that the plywood subfloor (perhaps 1/2″?) was installed over sleepers which rested on 3/4″ planking spanning between 2×8 joists spaced 16″ o.c. spanning 12′-0. So, from BELOW, they cut out the 3/4″ planking and screwed 3/4″ plywood to the underside of the plywood subfloor, then supported the 3/4′ plywood with pairs of 2×4 “ledger” beams screwed into the side of the 2×8 joists. (I can send a picture. :-) ) Right now, some of the tile has been removed so I can see the thinset grout atop cementitious backer board (not sure of the brand). They are concerned about the bounciness of the floor. I think that they have improved the situation, albeit unconventionally. I would like to propose that they screw the cementitious backer board into the 2×4 ledger beams below which will greatly increase the rigidity of the floor, reducing the likelihood of cracking. I read that you should avoid fastening cementitious backer board and wood underlayment where fasteners will penetrate into the floor joists. Is that true? Should the cementitious backer board be allowed to move independently of the joists?
Well, if you have read this far and can make heads or tails of it, my sincere thanks and great admiration is extended.
Hey Clark,
It is true that the backer should not be screwed into the joists. This shores up the underlying plywood and gives independent movement to the structure as a whole. In that particular situation, ummmm, I dunno.
I think I may just do what you’ve suggested in order to make the subfloor as stout as possible. It sounds like the lack of proper deflection is what probably led to the cracking. It may work.
hi roger great site you are a funny guy lol schooled and entertained great combo .my question is i was sold some plastic lathe and told this was good enuff when put down with thinset on top of single layer 3/4 plywood that it was then comparable to 1/1/4 plywood then thinset and tile.is this true thx m8- chris
Hi Chris,
What was being sold to you is the idea of a ‘jersey mud job’. They were very popular in the eighties and early nineties and beginning in the early nineties I started making a load of money replacing them – because they don’t last. It IS NOT anywhere close to comparably strong as the proper substrate thickness. Take the plastic lath back and trade it for some 1/2″ plywood. As a great, horrifying time waster you may want to google ‘jersey mud job’ ’tile’.
Hi Roger
I posted a question a couple weeks back re: a 1920’s house I’m remodeling. I’ve got the new tub in, backer on top of existing wall tile, window waterproofed & starting to tile. My question this time is re: the floor. I’m going to tile over the existing porcelain mosaics which are on top of 4″ of concrete notched into the floor joists on a floating tongue & groove floor (2nd floor bathroom). I had to remove a trench of the concrete & tile to install new plumbing. I’m at a loss as to what to do to fill that area in. Under the tub area I had attached new 2×8’s to the joists & added 2×4 cross framing w/ plywood on top. Will this work for the floor if I add the backer board on top of ply? What do I do at the edges where it will meet the existing floor? And do I need to put backer on top of the existing floor? I’m emailing you pictures in case I’m making no sense. Thanks for the help!
Yup, that’ll work just fine. Anything you can do to strengthen that floor before you tile it will help.
Roger, this website is beyond helpful. My house was built in the late 40’s and has the original bathroom complete with 4″ pale yellow tile halfway up the wall, capped with a nice black tile border, that runs all the way around. That’s all becoming sheetrock and new tile in the tub (old tile is out, vapor barrier is up, backerboard and tile this weekend). My question is about the floor. I have about 2″ of cement under the existing tile which would be hell to rip out. The tile is in good shape, the floor is in good shape (raised house and no water damage underneath), and everything is flat, so can I just tile over the existing tile? Or will my dog catch on fire? The wife really likes the dog so she’d be pissed. Any advice on doing this would be appreciated.
Hi Adam,
You can tile over existing tile. You will need to scarify the face of the existing tile (grind off the shininess) and use a proper thinset which specifically indicates it can be used in that application. Provided you take the proper steps your dog will not burst into flames – we hope.
If he does let your wife know I had absolutely nothing to do with it.
Sounds good. There was a linen closet that I took out. Where the walls were anchored to the floor, there’s now a 2″ deep gap. Also, the flooring in the closet was hardwood, which I assume I need to pull up before I put down tiles, which will give me another low spot. Any thoughts on what to do with those areas? I’m thinking fill with something (thinset?), install backerboard to raise it to the level of the old tile, and proceed from there, but again, the wife and the dog. And what should I do at the transition? Teach me oh wise one!
Hey Adam,
If you mix some deck mud (4-6 parts sand to 1 part portland cement) you can fill all those areas with that. Going over existing tile leaves very few options at the transition to the existing flooring. You can get a ramped transition piece (you can see the options at schluter.com ) or go with something like an oak threshold or similar.
Hello Roger,
I have a question about how to tie sills in with backerboard. My tile is 3/8″ with 1/2″ trowel, the marble sills that I would like to use are available in either 5/8″ or 3/4″ x 5″ wide, which means they would stick up past the surface of the tile if they were applied on top of the backerboard. So I guess I need to leave a “pocket” in the plywood/backerbaord for the sill so that it ends up flush with the surface of the tile. My concern is whether I will get cracking around the sill area since it won’t be fully tied with rest of the backerboard. Do you have any advice on how to handle this?
Eric
PS Your website is fantastic, thanks for all the help.
Hi Eric,
I’ve read this about twelve times and am still confused. Are you talking about a threshold rather than a sill? If so then yes, you can leave backerboard out where you are going to install it so it sets flush. Most of the time the threshold actually does sit higher than the tile itself – that’s normal. But you can set it flush if you want to. In the area you want the threshold just install a layer of 1/4″ backerboard rather than 1/2″ – that will take care of the height. You won’t get cracking as long as you still have a suitable substrate beneath the threshold.
If you’re not talking about a threshold I’m afraid you’ll need to draw me a picture.
Yes, you’re right – I meant threshold, not sill. Thanks for the advice.
Hey Roger, I am installing a 14 x 20 screen room. I want to tile the foor. I have 3/4 t&g treated plywood all glued together and to the joist. Do i need any more subfloor or is that good? I am going to put 1/4 permaboard down. Do I need a wafterproof membrane between the tile and peraboard, if so what to you suggest?
Hi Mike,
It depends on your framing beneath your floor. If it is typical 16″ o.c. joists with a fairly small unsupported span (i.e. your floor is solid) then you shouldn’t need to add anything there. The minimum recommended substrate height for your plywood subfloor is 1 1/8″ double-layer. So you need at least another layer of 3/8″ plywood over that with the seams offset, running perpendicular to the joists, and only screwed to the layer beneath it. You also need thinset between your permaboard and plywood layer to fully support the backer – no voids.
A waterproof membrane is completely up to you. I don’t know where you live or what type of moisture your room will be receiving. If you want it I would suggest ditra, not only can it be made waterproof, it will also assist with the installation’s durability. In fact, if you want to you can replace the permaboard with the ditra and get 2 for 1. Ditra can be installed directly to your plywood.
Hi Roger,
Your website has been a HUGE help in my shower tiling job. Next up is the bathroom floor. A couple of quick questions:
1. My bathroom is L-shaped (the long part is the vanity/sinks, the shorter would be the shower/toilet area). Everything I’ve read says to snap a chalk line through the middle of the room and work from there – which would seem to work in a regular shaped room. Any suggestions on what to use as center?
2. I’ve seen z-bars used for tile to carpet transition. Do you recommend? If so, does the tile side get set into the Thinset under the 1/4″ HBB? Or under set into the Thinset under the tile?
3. The aforementioned shower tile project. They’re up and look good, but have some Thinset here and there that dried to the face.
Any ideas on how to remove the thinset from the porcelain tiles?
Thanks in advance. Again, you’re website is really fantastic.
Greg
Hey Greg,
With an L-shape you don’t need a center line. Start with a full tile in the doorway and against the tub then measure from there to ensure you won’t have a small sliver of tile on the opposite wall from the tub (or anywhere else). If not – that’s your layout. If so then move the tile 1/2 a tile width away from the tub and start there. You don’t necessarily need a center line – no one should be in there with a tape measure an/or lasers to ensure you are perfectly centered. Everyone will notice, however, that there are small slivers of tile installed somewhere – eliminate those and you’ll be fine.
I don’t like z-bars for tile and carpet. You can simply install the tack strip about 3/8″ away from the edge of the tile and tuck the carpet there – no need for a z-bar at all, it’ll stay (as long as you stretch the carpet). The bottom arm of the z-bar is actually installed under the tack strip – nothing gets installed from the tile side.
Scrape the chunky parts of your thinset off with a (FLAT – no dings) putty knife and scrub off the remainder with a scrub pad. It’ll come right off of porcelain.
Hey Roger,
I will be laying some tile on a covered front porch in Minnesota (Cold!) I bought additive for the mortar to help with freeze/thaw. It had nasty outdoor carpet with plywood under which has become un-leveled with spots popping up here and there. Should I use a rubber waterproofing membrane with mortar underneath then tile, or should I put some cement board on top of that also, many thanks, and I hope my dogs will be fine!
P.S.
It is 1″ plywood with 2 X 10 joists
Are my dogs on fire yet?
Dogs aren’t on fire yet.
Hey Adam,
If the plywood substrate is unstable as you’ve said then it should be removed and replaced with a new piece. Over that you will want a suitable substrate for your tile installation. There are several available, just make sure they are approved for freeze-thaw conditions and the mortar and additive you’ve purchased are compatible. I would put two new layers of ply, 1/4″ cement board, then your membrane and tile. That’s normally how I build them in Northern Colorado – it works.
Roger,
Your website has been indispensable throughout several stages of my bathroom reno! We gutted the bathroom to the T&G floor and wall studs. We added 1/2″ ply and 1/4″ Hardie (using thinset, per your article!) to the floor and will probably sheetrock the walls next (no tile on the walls). My question is: What’s the best order to install the door jambs and porcelain floor tile? I can envision aesthetic differences, but I think there should be something more convincing one way or another.
Thanks!
Hey Charles,
If you have a choice always, always install the jambs and trim over the top of the floor tile. Do the porcelain first then finish up the trim. When I don’t have the choice I always undercut the jambs so I can slide the tile beneath them. If you’ve ever look at the tile in someplace with either metal door frames or any other installation where the tile was cut around the jambs you’ll notice it looks like ass – I think it does, anyway.
I’m laying 1/4″ Durock over 3/4″ weather rated ply subfloor for 13″x13″ ceramic floor tile. The Durock says use a V- notch trowel for the thinset to subfloor. Reading here it looks like you suggest 1/4″ from experience? Or is that for the Fiberboard stuff only, and you use something else for Durock?
If you still use the 1/4″ trowel for beneath the Durock also, do you slather on the thinset pretty thick and in different directions so there’s still thinset remaining along the entire length of the trowel, or do you scrape down to the subfloor with the edge of the trowel, leaving thinset only at the notches?
Hey Todd,
It really depends on how badly out of flat your subfloor is. The worse it is, the bigger the trowel and more thinset you want beneath the board. All of the backers go down essentially the same way. My go to trowel for that application is actually a 3/16″ v-notch trowel, but I’ve used about every one in my bag for that purpose.
Ok, thanks Roger.
Do you install the same 1/4 inch gap when transitioning to hardwood flooring?
How would you finish the tile part of the job when transitioning to hardwood flooring? They’re the same height. Specifically, do you set the grout gap at the same reveal as the rest of the tile grout spacing, or is it larger or smaller?
Do you use grout in that gap, or color matched silicone?
Hey Todd,
I usually only leave about 1/16″ gap between tile and wood. You need to silicone that gap – grout will crack as the wood expands and contracts.
It just so happens that there’s a joist running across the doorway right where I should be putting rock screws along the edge. The 1.25 incher rock screws do poke through the subfloor, and will hit the joist. What’s the best way to handle this situation? Sink screws along the edge properly, or back off the edge and not hit the joist? I’ve already done the backed off version, but now I’m paranoid the edge will move, so would consider adding some along the edge through the hard thinset. I like my dog and don’t want her to burst into flames.
Hey Todd,
Yes, that edge will move. As long as that is the only place you’re nailing into the joist it’ll be fine, but you should screw down that edge. I don’t want your dog to burst into flames either!
Hi! Thank you so much for your site. It cleared up a lot of iffy information I found on the internet. We are in the process of remodeling our guest bathroom. We followed all the instructions above, but I would like for you to explain something….my husband could not understand why we had to put thinset under the cement board PLUS screw the boards down to the subfloor. He didn’t think it made sense.
Hi Narenteria,
The thinset is beneath the board solely to fill hollow areas and fully support the entire board without open spaces beneath it, which leads to movement. Thinset does not adhere the backer to the floor (over the long term). The screws are there to secure it to the subfloor.
Hi Roger.
My previous projects have been small rooms 2 or 3 sheets of hardiboard. New project is 6 rooms of tile about 900 square feet. First question is does it matter if the hardiboard sheets lay in the same direction? Second question is you say to sagger your seams from your pictures you just stagger the short side but run the long side in a line?
Hey Dennis,
You can stagger the long side or the short side – or chop it up and stagger them all. What you want to prevent is having four corners meeting at the same point. That’s what I mean by staggering the joints. The hardi does not need to lay in the same direction. You just don’t want the four corners meeting or any of the hardi seams directly over the seams of the wooden subfloor – you want to offset those as well.
Hello,
We put down the tiles in our kitchen/family room area. We put the backer board (Fiber) with caulk and we used the screws for the backer board and taped everything. We notice that in certain areas that the grout is cracking and popping out. We covered about 600 sq ft of floor with ceramic 18″ tiles. Is there any solution to this situation? I was looking into grout caulk. Is that a viable option? We really can’t afford to take these tiles up. I hope there is a solution. Thanks.
Hi Charmaine,
I don’t quite understand the statement ‘we put the backer board (fiber) with caulk and used screws…’. Do you mean you installed caulk beneath the fiber backer board? If so, that right there is the problem. Using caulk or any type of construction adhesive (another common misconception) beneath your backerboard will leave hollow areas between every bead you put down. Hollow areas = movement. Caulk also does not cure solidly – it’s meant to move. Am I understanding you correctly?
I’ve never heard of any such thing as ‘grout caulk’. The closest you’re likely to find would be a polyurethane-based grout which will allow for more movement than normal, it’s also fairly expensive and takes about a week to cure (last I heard). There may be new types of these grouts available that have a shorter curing time, but they are still expensive. Using caulk for grout will not work – and will not stop the cracking.
My question is after you Hydroban the wonder board how do you waterproof the escutcheon plate hole? Seems if water got bettween the tile and Hydroban it may come out at the hole and get into the wall? Do I just silicone the edges of the cut? Thanks
Mike
Hey Mike,
Silicone between the tile and wonderboard around the cut. If you’re using a moisture barrier also silicone the barrier to the back of the wonderboard.
Hi Roger,
Thank you for the great website!
For our bathroom floor, the installer plans to use RedGard over the 3/4″ T&G plywood subfloor and then tile directly over that using flexibond.
I’m having a difficult time understanding what the backerboard would accomplish in this situation since tile can be bonded to RedGard in other applications. When the tile is bonded directly to the backerboard, I think the concept is that the two materials are alike enough to allow them to move together with variations in temperature and moisture content. This allows the bond to remain strong. However, with a layer of RedGard between the backerboard and tile (as in shower wall assembly), it seems the moisture content of the backerboard would be much more stable than that of the tile. This causes me to question the importance of the backerboard in floor installations.
To compound the issue, the RedGard directions aren’t exactly clear when it comes to installations over plywood. My installer says installation over plywood is allowed. I’m not sure whether we’re shooting for “crack prevention membrane” (plywood allowed?) or “waterproof membrane” (plywood not allowed?).
Please help me understand what the purpose of the backerboard is for floor installations (we don’t have a dog…). Maybe then I can talk the installer into using the normal backerboard method.
If we end up going with the backerboard, why should or shouldn’t we use RedGard on the bathroom floor? Our bathroom floor always seem to be wet. If we do use RedGard with backerboard, where should the RedGard go (on the plywood, or on the backerboard)?
Maybe I should get a dog to help make your explanations easier. I hear people with dogs live happier lives, too.
Thanks,
Bill
Hi Bill,
If you are using redgard on a floor it is utilized as a crack-prevention membrane. HOWEVER! The crack prevention properties will not compensate for an inadequate flooring substrate – which a single layer of 3/4″ t&g is. For that matter – ‘crack prevention’ is not the proper term, crack suppression or crack isolation is. The function of a crack suppression membrane is to prevent cracks from concrete substrates from transferring through to your tile installation. It does not prevent cracks. If you install tile over that single layer it will crack – period. The redgard instructions are not clear on this method because it isn’t made for that method, that isn’t what it’s for.
Industry standards (TCNA method F150-09) require a minimum of 1 1/8″ double layer of plywood for a wooden substrate. That is standard, and minimum. Redgard isn’t going to change that. Redgard is not meant to be utilized as any sort of prevention of cracks due to inadequate substrates. This doesn’t even take into account proper deflection which is a result of your floor joists. The redgard can be used in that application as a waterproofing membrane if you want it provided an additional layer of plywood is installed. At the very minimum the 1/2″ backerboard should be installed. Redgard can be installed directly onto to backerboard.
Ok….So I’m recently divorced and I’m on my own to fix up my house!!! I feel extra stupid because other post are much more technical then mine. Here’s my question, I have laid the backer board and have not butted them together however there is a small gap between the board and the wall about half an inch worth. Is it ok to fill in the gap with thin set? By the way my dogs are out
Hey Kat,
Actually that is completely correct! There should be a gap between the wall and backerboards to compensate for movement. Do not fill those with thinset – it defeats the purpose. Leave them open and do not butt your tile against the wall either – leave about a 1/4″ gap. Either cover that up with baseboards or fill it with silicone.
Roger you are my hero!!! I’m scared,nervous and worst of all running low on funds for this job. :eek:. Your page has really put things back on track for me. Thank you sooooo much. So I now have the backer board down. I only have about 40 tile to lay however its in my entryway. So in other words the tile will go from the door to the stairs. Do you have any tips for this?
Hey Kat,
Glad I could help. As long as your backerboard is installed correctly you have a nice, solid substrate. It’s usually easier to cut all the tiles and lay them in there before mixing up your mortar. You can make any adjustments before you start placing tiles in mortar. It’s much easier to change something you’re unhappy with before sticking them down.
Hey Tyler – you need to take that shower pan out.
Just kidding. You can install 1/2″ ply over the 3/4″ up to the shower pan and you’ll be just fine. Get a jamb saw and undercut your door jambs to slide the 1/2″ under them. Be sure to leave an 1/8″ gap between sheets to compensate for movement and do not screw the second layer (1/2″) into the joists – only into the first layer (3/4″). Your dog is safe.
Few…You had me goin for a second! I was just curious about your thoughts on using DitraXL vs. Double ply plus backer. Seems like it would be perfect but can the travertine/marble basketweave mosaic sheets consisting of 1″x2″ and 1/2″ cuts be used on that substrate? On another note, you have a good eye for design and I would like to pick your brain about how to deal with an angled ceiling over the shower. The bathroom is a 7′ square with a corner shower. The wall opposite the door (vanity and one side of shower) is 6″ hight, then angles into room 37″ to meet 8′ ceiling. The other side of shower has showerhead above the 6′ hight. The entry of shower is on neo-angle. My question is, were do I stop the tile so it looks approriate and covers all wet area. The drywall co. put durock cement on walls including 12″ outside shower on both sides. They didnt think to just put in a nailer!?! Even better, the angled ceiling is drywall. Oh, And no plastic behind backer! I plan on having frameless glass installed, some day, in the end and dont know how much of ceiling to tile. I’m sorry, its late and I’m not sure if I am making sense anymore. Any ideas? And dont tell me I have to tile the whole darn wall….
Hey Tyler,
Ditra XL is good stuff. Unfortunately it is only recommended for 2×2 and larger tile. With tile that size I would stick with the backer to be solid.
As far as design yes – I have an eye for it. I do, however, need to actually see the space you’re trying to do this in. Using only descriptions may lead to me giving you incorrect advice and you following it – and me looking like a bigger jackass than I already am.
I can tell you that with what you’ve described as your substrate you can use kerdi to waterproof any or all of it and you’ll have a waterproof shower – no matter how badly the drywall company screwed it up. 
If you can send me a picture of your shower to Roger@FloorElf.com I can look at it and give you bad advice anyway. 
Thanks Roger for all your help!
I apologize in advance for my photos, best i could do with camera phone.
I closely inspected backer in shower and have couple new concerns.
Backerboard ends before shower head. I suppose this and any other exposed drywall to shower is what i should cover with Kurdi, correct? Or is water at that height of minimal concern ? One area where cement board butted together. Can i just scrape out gap with carbide tipped scoring tool? (Its not along entire board just about a foot long section.)
Also found weak unsupported seams on either side of shower pan. What’s best way to fix this? Lastly the cement board along lip of shower pan protrudes out on one side, but is flat. I’m guessing not pertectly straight studs. Does the tile just come down over this and fill in all/any gaps with silicone? No plastic, so will silicone and redgard combo do the job?
I almost forgot, would love your idea on tiling ceiling angle!
Hey Tyler,
Yes, your shower should be waterproofed at least up to the shower head. Yes you can scrape out the gap with a scoring tool. Fill the gap between the unsupported edges with thinset, apply alkali-resistant tape over it and smooth it out with more thinset. That will lock them together somewhat once it cures. Ideally you should remove one side and screw 1/2 of a stud to the remaining, then re-install the other piece and screw it to the other 1/2 of the stud.
I would tile all the walls to the ceiling and stop it directly above the edge of the tub. Then run your bullnose from floor to ceiling. Kinda like this one I did: Really Blue Shower Kinda. Short of that run your bullnose across the top level with the horizontal wall.
We didn’t tape the joints on the backerboard. Now we have hairline cracks. is there a way to fix this without taking up everything?
Hi Jessica,
Unfortunately no, the only solution is to take it up and install it correctly. The cracks are appearing because the substrate beneath the individual sheets of backerboard is causing them to move in different directions or at different rates than one another. There is no way to remedy that without removing what you have and installing a proper tile substrate. Sorry.
Hey Roger,
My question(s) are gone from here, and the last one wasn’t answered. Could you please bring me up to date?
Thanks,
DJ
Hey DJ,
Nothing gets deleted from my site.
If you click the ‘previous comments’ link below the last comment on this page it’ll take you to all your questions – as well as my answers. I keep the comments down to 50 comments per page to keep it manageable. 
Today, our plan was to lay down the Fiberock in my 13.6×17 kitchen. Although after reading this site, I’m not sure if this is wise anymore.
I bought this older house and stripped the floor down to the joist. I replaced the subfloor with 3/4″ plywood with lots sheetrock screw. Now, we want to lay down the 1/4″ fiberock over thinset. Then, 6×24 porcelain tiles over that w/ thinset in between. My floor right now doesn’t really flex when i walk on it (I’m about 110/lbs) but does when my 180 lb husband walks on it.
Is the 3/4″ plywood suffiicient or do I need another layer of wood on top of that? I’m trying to keep it low so that the transitions to the other rooms aren’t going to be a toestubber every time.
I read somewhere in this site that sheetrock screws are not strong enough for floors. Should I swap them out or simply screw down more screws between what I already have down. What screws should I use?
Should I use the 1/4″ notched trowel for both applications (Fiberock and tile)?
The instruction for the Fiberock is to leave a max of 1/32″ between the sheets but I read here to leave a bit more. Can you clarify for me? I will be leaving a min. of 1/4″ between the walls and the floor.
Should I screw down each sheet as I lay them down or after I have them all in? (In case we need to make any ajustments.)
Thank you so much in advance for your help.
Hey Shang,
You should have a minimum of another layer of 1/2″ plywood over your current flooring. 5/8″ would be ideal. Sheetrock screws are not made for floors – they’re made for sheetrock
The are not strong enough to deal with the stresses placed on your floor. They should be replaced with deck screws – they are readily available at any big box or hardware store. The sheetrock screws should be removed but you should be fine if you leave them.
If you would like to forego the additional plywood you can eliminate the 1/4″ fiberock and use DitraXL over the current plywood – it’s rated for a single layer of plywood. You should use 1/4″ notch trowel for beneath the fiberock and a minimum of 3/8″ for your tile. 6 x 24 is considered a large format tile – you need a flat floor and full coverage – bigger trowel. Never seen the 1/32″ gap between the sheets and I’m unsure what application that’s specified for but on floors you should have 1/8″ gaps between sheets and 1/4″ around the perimeter. It’s easier to lay them all in then screw them down, it allows adjustments as necessary.