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.
Thanks for an extremely helpful Blog. Just one thing – We’re approaching our first DIY tiling project and have been trying hard to follow the rules.
We purchased Durock backer and I have the thinset to fill the voids and the proper screws. We’re at the point of dry-setting our backer board and I realize that our room is less square than previously thought. What this means is we have sheets meeting on one end and gapping 1 1/2″ on the other end. My question is – do I try to cut a tiny sliver of backerboard to fill this void, or do I apply thinset to fill it – cover that with the fiberglass tape – and then “mud” with more thinset?
The issue is, not only do I have a gap – it’s running down the center of the room the length of one sheet. It’s my own fault for measuring from the wall and not from the other sheet, I know.
So – do I need to try to fill the gap with Durock or thinset – and can I leave the gap towards the middle if properly filled, or do I need to cut a new sheet so that the gap falls at the edge of the room rather than the middle.
I’m vaguely terrified of screwing up this DIY project as it’s my first tiling job so any suggestions appreciated.
Hi Nyteri,
Can you butt those two boards together (with 1/8″ gap) and cut the sliver against the wall? That would be the best solution. 1 1/2″ is too big to have just thinset and tape over it but if you have the sliver at the wall rather than the middle of the room it’ll be better.
Thank you for some of the tips and great humors. Currently, I am in a minor pickle. On a 1928 home, I gutted the bathroom to the bare studs and floor joist. I took the time to make sure all joists are level. Knowing that I had to put a cast iron claw foot tub down, I put two layers of plywood; 3/4″ CDX over the joist and 1/2″ glued and screwed over that. I worked hard to make sure that there is no bouncing on any of the plywood.
Pryor to adding the 1/2″ plywood to my plan, I had already purchase 1/2″ Durock. With the thinset proper screws (thanks to your tip), I placed the cement board down. This is followed up by taping and adding Thinset over that.
Alright, I am set. We waited a week and did a dry run with the tile (5″ x 24″ wood grain look) in the bathroom. These titles have to stagger throughout the room so it can look like hardwood floor.
During the dry run, I found that the floor is not level in small part of the area close to the entrance to the bathroom. Go figure. The high spot is where the two backer boards meet and it extend along the tape for about 2 feet. It could be the low spot on the corner of the room. The rest of the room is level.
Should I grind down the taped section to make it level? Or add floor leveler to that section?
One other question, when do I make pipe holes for the tub? Before I place the tiles or after?
Thanks
Dan
Hey Dan,
It’s normally better to put self-leveler in the low areas. If it less than 1/4″ out of level, though, you can simply make up for that with thinset as you tile. I would cut the holes for the pipes now, stub them up through the floor, then cut the tiles around them. You can also do it after you tile but you run the risk of nailing a screw unless you take care to keep them out of the area of the plumbing holes.
Thanks Rodger,
I checked out laticretes website and they state that exterior glue plywood used in interior applications (such as BCX plywood) is a suitable substrate for Hydroban. I guess really I just need a proper substrate for the tile to stick to and plywood doesn’t cut it.
Regarding Ditra, someone told me that they have installed it by placing modified underneath it and then doing a skim coat of non modified on the top, filling in all the waffles and smoothing it out with a flat trowel. Then they let it dry overnight. They come back the next day and use modified with porcelain tile because now the modified is sticking to a cement based back. Thoughts on that process?
Nothing wrong with that method with the ditra at all. You will still lose your warranty from schluter, though.
I am getting ready to tile a bathroom in a log home. The bath room has a beam running underneath it in the center which is creating a hump and the floor slopes a little over an inch in each direction. The room is about 12’X8′ and the hump in the middle is across the short side of the room. There is currently 3/4″ OSB as the subfloor on 2X10 joists on 16 inch centers over a 12 foot span. Here’s what I am planning and would like your opinion.
I plan to put a 1/4″ layer of wonderboard over the entire area. By the time I add the 1/4″ wonderboard the highest point of the hump will put me as high as I want to be to tie in to the bedroom hardwood. Then add a 1/2 ” layer against the outside walls. (basically as filler) I then plan to float the entire area with LevelQuick to level the floor. Is this the correct procedure? If not what do you recommend? If yes then is there any advice you would give me. I’ve never worked with a Self Leveling compound.
Thanks so much,
Brad
Hi Brad,
You can do that but you can actually get rid of the 1/4″. SLC can go directly over the plywood provided you use the primer for it. You can add the filler pieces (get thinset beneath them) then go over the whole thing with slc.
Hi Rodger,
I am about to embark on installing some floor tile in my brand new house. I have larger floor trusses that were set 19″ on center. I talked to a few tile experts in the area and they two suggested using ditra to help with potential deflection. The other two stated that ditra has problems and did not recommend it. One reason I’m leaning towards not using ditra is because it states you must use non modified mortar. I have porcelain tiles and from what I have learned it is always best to install porcelain with a modified thinset.
I have also been reading the tile council of America book and it states that I could add 1/2″ plywood to my 3/4″ subfloor as an underlayment, add a crack isolation membrane (such as hydro ban), and then use a super flex thinset. Is this acceptable or do I also need to add a backer board as well? I was just going to add the 1/4″ backer board and no 1/2″ plywood but my expert suggested at a minimum I need the 1/2″ plywood.
I’d be interested in your opinion. Thanks!
Hi Hogan,
There is absolutely nothing wrong with unmodified with porcelain over ditra. It works, and it works well.
The 1/2″ ply would be fine but you’ll not find a manufacturer (to my knowledge) that accepts the use of their membrane over straight plywood with tile bonded to it. You need a proper substrate under it, usually backerboard. So you can use 1/2″ ply with 1/4″ backer (with thinset beneath), then the membrane and tile.
Great site; now I’m only partially confused. I’m trying to install new bathroom tile over a subfloor damaged by flawed plumbing (that’s a whole ‘nuther story). Original floor was 8 inch joists on 16 inch centers with 9 foot span. That tells me that ceramic is OK, stone is out. Flooring was 6 inch diagonal SYP and 3/4 particle board (yes, in a bathroom, an indication of the thought that went in to construction) and linoleum. Adjacent bedroom is carpeted. The particle board (actually, the crumbly remains) has been removed. The SYP has been treated with a penetrating epoxy to eliminate future dry rot. I know I need thicker subfloor for support, so 1/2 inch plywood on top of that, screwed at 6 inch grid. I plan on 1/4 inch backerboard, then thinset with embedded heat tape, then ceramic tile. That brings me to about 1/2, maybe 3/4 inch above the adjacent bedroom rug, a small enough transition so as not to present a trip hazard. Now I’m reading about moisture/vapor barriers and that’s where the current confusion lies; do I need one? Can I use Redgard or Aquadefense? I don’t want to add any more thickness than I have to. Will the backerboard/Redgard/thinset create an adequate bond? Is 1/4 inch backerboard thick enough?
Hello! Thank you for providing such a wonderful site! My question is basically me trying to not have to pull up what I already did in Room #1 by promising to use thin set in Room #2, if just as necessary. A friend who has done much beautiful tiling in his own house told me all i had to attach my cement board with was liquid nails and screws. The structure is new construction,(an addition on a 114-yr old house) if that makes any difference. So, I’ve already done the first room using the glue and screws and moving on to the second one, I wanted to research seams and found you, albeit a day late. I also didn’t leave gaps between all the boards. (Boy, this is sounding worse). Will it be okay or does it sound like a redo?
And while I am at it, I’ll ask my seam question… Is there a certain amount of space you want to leave between the wall and a seam if the seam is running alongside the wall? Thank you profusely for your help, insights and levity for these situations!
Hi Becky,
Unfortunately you really need to pull that up and redo it. Thinset is there to fill any voids and fully support your backer. Liquid nails, due to the method by which it’s applied, will actually create voids, which creates movement, which causes stuff to crack.
There is no real rule as to how close you can have a seam to a wall but you want it at least two inches away from the wall in order to tape and mud it.
Hi Roger,
I love your site. So much great info in one place!
I want to install 12 x 12 porcelain tile in a bathroom. Right now sub floor is 3/4″ OSB. I don’t want to add a lot of height to the floor, I would like to just add 1/2″ cemtent board, if possible. How do I know if I need to add more plywood to the existing subfloor? Can I figure the deflection of the floor and add extra supports between the joints if needed, rather than adding more plywood on top?
Hi Amy,
Deflection and layers of plywood are two different things. The second layer *also* acts as a sheer, or slip, joint between the layers. What this does is allow the floor to compensate for any differential movement in the joists. If one swells to the left 1/8″ and the one next to it swells to the right 1/8″ you have a single layer of ply that will be pulling apart by 1/4. The second layer of ply compensates for this. If you use a membrane such as ditra you can get away with a single layer most of the time with ceramic or natural stone. If you beef up your joist system enough you can also usually get away with it using cement backer.
You can go here to figure out your deflection: Deflecto
Hi Roger,
I’m having 24″x24″ porcelain tile diagonally installed in my 1967 bungalow that has 3/4″ thick plank subfloor and (1) layer of 3/8″ ext. grade plywood subfloor. 2×10 floor joists, 16″ OC.
About 150 sq.ft was already installed over heated floors but the original contractor quit after probably mis-quoting the first stage. This 150sq.ft area that was already tiled has (2) layers of 3/8″ ext. grade plywood on top of the 3/4″ plank subfloor. I’m not sure if they was glued to each other or not.
With an additional 620 sq.ft of floor remaining to be installed, I have been told by a couple tile installers that you don’t need to install cement backerboard and you can get away with another 3/8″ layer of plywood glued to the original 3/8″ ply subfloor and add construction screws every 4″. I have been told this will eliminate the squeaks and be strong/sturdy enough to support the tile without having the grout cracking.
After gluing and screwing the 2nd layer of 3/8″ plywood, self-leveling concrete will be poured down. Then comes the tiling.
Basically, everyone is telling me the two layers of ext. grade plywood glued and screwed will work fine.
What are you thoughts?
Thanks and appreciate the site,
Curt
Hi Curt,
It will work fine provided you do not glue it, and just screw it. If you want to glue it you want to use a full-spread glue, not the stuff in caulking tubes as that will create voids between the two layers. If you are using slc over the upper layer it will work fine.
Installing porclean tile in a 300 square foot kitchen. About 1/3 complete installing my 1/4″ thick hardi board with mud under it. Just realized I did not stagger my seams….argh. Should I fix this or just stagger the joints from this point forward. Plan to tape and mud the joints as required.
Hi Kevin,
Unfortunately you really should fix that. The seams NEED to be staggered. Sorry.
Hey Roger –
Just wanted to say this is an awesome site, I just tiled two showers in our new house and going to be tiling the floors next and was hoping to get some pointers on prepping the floor (new construction). I read another article about using thinset under the backerboard but was told by an in-law that that wasn’t required (he didn’t use it when he installed the floor @ our old house – hence the cracking). I feel a lot better about tackling the floor now. Thanks again.
Hi Greg,
Sorry for the delay, been out of town at the new Schluter facility all week.
Provided your floor has proper framing to support a tile installation you just need a double layer of ply over your joists and a proper tile substrate. If you are using backerboard it is absolutely required to have thinset beneath it.
I’m preparing a 268 square foot kitchen. Travertine tile. 1 1/4″ particle board subfloor. 1/4″ hardibacker. the floor is not completely level or flat. Doing some sanding of seams and high spots. started with a belt sander and now likely going to a rent a floor sander, but would like to to levelquick the floor.
should I levelquick on the subfloor(below the hardibacker and thinset) or on top of the hardibacker?
Hi Morgan,
You should first get rid of the particle board. It has absolutely no place beneath a tile installation at all. It has nowhere near the structural stability needed and it if sees the tiniest amount of water it swells to almost double it’s size. It has to go.
And yes, I know that’s not what you wanted to hear. If you install levelquick in a tile installation you either do it above the cement backer or you do just the level quick with no cement backer. Backer can not be installed over it.
I have 2 x 6 floor joist span 13′ 16” on center with 3/4” particle board.
joists can’t be beefed up at all.
would like to install tile ,
What should I add to sub floor?
or is this just to much weight for my joists?
THANKS for your input.
Hi Steve,
Your deflection currently stands at around 140 – less than half required for ceramic or porcelain tile. Your only option to tile over that would be to cut the span down to a minimum of 9′, which will get you to 388 (tile requires 360 maximum deflection). I know you said they can’t be beefed up, but gave no specifics. Sistering or adding joists is not the only way to accomplish that.
If you can not do that then your framing will not correctly support a tile installation. Should you still choose to move forward with tile I would add a minimum of 3/4″ ply over it with a membrane such as ditra.
Hello
I have an existing quarry tile floor which is fairly flat with no loose tiles, and an adjacent timber floor. I am proposing to lay ceramic floor tiles over the two areas and looking to use a tile backer board as part of the floor prep. so wondering if the backer board can be fixed over the quarries in the same way ? using plugs with the screws for the mechanical fix ?
Good site by the way…..very imformative
Hi Tony,
The quarry tile needs to be removed. There’s no real way to attach backer over it long-term and guarantee durability.
Roger,
I had a recent tile job, and I know the installer used thinset under the concrete board. I also watched to make sure he taped all seams. I am not sure that he used any thinset over the seams, other than what he used to set the tile. Assuming that’s what he did is this acceptable, or can issues be anticipated down the road?
Thanks… Chris
If there was thinset installed under the backer and the seams were taped and mudded then it should be fine. Are you just asking to check or do you actually have an issue currently?
Just checking. What I suspect is that the installer taped the seams, and did not mud them. The mud, so to speak, would have happened while he was setting tile. Is that acceptable? Or do the mudded seams need to dry before setting tile? Thanks again.
That is acceptable, I do it as I’m installing the tile as well. It does not need to be cured before installing the tile.
Roger – thanks once again. I will sleep better at night now.
Roger,
Going to tile a Great Room, Kitchen Hallway, and two Bathrooms with 3/8″ X 6″ X 24″ porcelain tile that looks like wood planks. The tiles are actually 5 7/8″ X 23 7/8″ and the manufacturer recommends a 1/8″ spacing. I would prefer a 1/16″ space with grout to closely match the tile so the grout line will be less noticeable, is this O.K.?
Was planning on using the 1/4″ Hardi Backer Board for underlayment, but cannot find 1″ Hardi Backer screws and don’t want all the tips of the screws showing through the ceiling in the basement. So I decided to go with the 1/2″ Hardi Backer Board. Looked at Hardi Backer Boards at Home Depot and discovered that according to their spacing of screws I will need 48 screws per sheet, quite expensive. Question number 1, what size trowel would you recommend for the thinset between the subfloor and the underlayment, and should I use a square grooved or v notched trowel?
My next concern involves the tiles being perfectly level on the floor so that there will not be any spaces under the baseboard or cabinets. Looked at a new product from QEP called Tile Leveling Clips and Wedges for leveling tiles. it appears to me that these clips will leave 1/8″ space under the tiles for the thinset, but again they are quite expensive $9.97 for 96 clips. Could I just put a 1/8″ spacer under each corner of the tile and make sure that the tiles are pushed down firmly on the thinset and spacers when installed?
Thanks for your help………
Ken
Hi Ken,
the ability to use 1/16″ grout lines depends on how flat your tiles are. If you place them face to face are they solid against each other the entire length of the plank? It would be my guess that they’re not. Squeeze one end together tightly and the opposite end will likely come apart. That’s going to create a problem with uneven edges. When offsetting them the corners (lowest part) will be against the middle of the edge (the highest). You should use a 1/3 offset rather then a 1/2, which will lessen it some, but using a larger grout line also helps with it not being as noticeable.
A 1/4″ x 1/4″ square notch trowel for under your backer should work fine. The lash system (leveling system) you’re talking about works well, but it does require more thinset beneath the tile. You CAN NOT install spacers under each corner. This leaves the corners unsupported and will lead to grout, and possibly tile, eventually cracking. You can do the same thing with thinset, it just takes time.
You mention counter sinking the screws on the backer board. If the screws do not counter sink, should these be removed and re-done until they do counter sink. The reason I ask this is because if you use tape over the seams and add thin set motor to the tape, this results in an uneven surface on the backboard along seams. Therefore one would assume that you would need to compensate for the rise of mortar over the seam by adding additional tile mortar. I would think you would want the backerboard surface to me perfectly level and bump free. Can you clarify this a bit more? Thanks
Hi Mark,
Yes, you should have them countersunk. That’s one of the reasons for using the right screws. You can make up for a bit of inconsistency with thinset as you install tile, but it’s always ideal to have a completely flat substrate before tiling.
Thanks for the response, very helpful. Still a question remains – if you tape a seam, won’t that become higher than the backerboard, resulting in an uneven substrate before tiling. (and yes, I am using backboard screws…they just don’t always grind down flush – may have to pull the higher ones up and use a countersink drill bit, and then put the screw back.)
You’re talking about 1/32″ or less. If that interferes with your tile installation then you aren’t using nearly enough thinset beneath your tile. Countersink bits get chewed up very quickly in backers. It’s easier to back the screw out and drive it in again. A running start, so to speak.
Hi Roger, and thanks for all the good advice. I have a 1957 home and the kitchen floor has been skimmed with plywood twice. The floor is a little over 1 inch thick now (two plywoods and three linoleum type floors), and I am looking at another 3/4 or so with backing board and tile. The last plywood was glued and screwed to the old floor, so I can only remove the ENTIRE plywood skims as one piece (after cutting it into manageable squares with a circular saw). I would like to install 5/8 cement board directly onto the 3/4 thick diagonal lumber put down when the house was new in ’57. With thinset of course because you know how I love my dogs hehe.
Mark
Hey Mark,
It would be better with an additional 1/2″ ply over those planks under your backer.
I’m laying down tile and I noticed that on top of my sub floor I have plywood. If I’m installing Wonderboard 1/4 should I remove the plywood or just lay it on top of the existing plywood? I’m going to be putting down ceramic tiles.
Thanks.
Hi Richard,
Install your wonderboard over the existing plywood. Make sure you have thinset beneath it.
Thank you. I really appreciate the fast reply and the reassurance.
Hi Elf — great site! Super useful, informative. Thank you.
First time diy’er here, swinging for the fences with a kitchen tile installation (gulp).
I’ve mudded beneath, screwed and taped my backerboard. As i lay out the tiles on my backerboard, some do not lie flat, because of occasional backerboard screws that did not countersink (about 1/16 a rise) or, worse, i tried to feather the thinset over the taping but i got little skatepark (as you put it) bumps that are between 1/16 and 1/8 above the flat surface of the backerboard. So, some tiles are already lipping around that amount.
Now, the thinset calls for a 1/4 sized trowel. Will that thinset “take care” of those bumps, as i install the tiles and make them flat with back buttering etc? That is, can I work with the situation i have, or do i need to redo the underlayment?
Thanks,
e
Hi Eli,
If you use a 5/16″ or 3/8″ trowel you should be able to go over those screws with no problem. You may also want to try to back the screws out about halfway and driving them in again. Most of the time that will allow them to dig deeper since you already have most of the hole already set.
Thanks Roger — helpful advice.
So that deeper thinset layer will also deal with the bumps on the taped seams (they cause more of the issue with the tiles dry laid out — the tiles will wobble along a diagonal axis, ie.
Your site is so helpful — much obliged.
Yes, it will deal with those as well.
So my first and only tile job had a couple mistakes. After looking at the hairline cracks in my ceramic tile exactly where the backer board comes together, I had some one tell me I did not need tape over the seams. Now I am ready to install a more durable porcelain tile. Do I have to start over from the sub floor?
Hey Rex,
If the backerboard is in good shape and salvageable you may be able to just tape and mud over the seams. This is, of course, provided you’ve installed thinset beneath the backerboard. If the backer is questionable I would start over.
Thanks for the straight forward info! I have one question? My plywood sub-flooring was damaged quite a bit when the old parquet flooring was pulled up. How good is the thinset when it comes to filling in any chunks of wood missing. I gauged out some areas that may need to repaired.
Hey Randy,
It depends on whether you only have a single layer of ply over your joists. If so then it won’t do much good as any movement at all will cause it to crack. If you have a double layer, which you should, then you can fill it up to about 1/4″ or so without any problem.
Thanks for some awesome tips! I’m about to put Durock down, but I think I may have to alter my subfloor first.
I pulled up the multiple layers of linoleum, vinyl tile, hardwood to get to my subfloor. I found it was only a 1/2 inch so I added a second layer of half inch osb. My advisor told me to make my seams as tight as possible, which I did, but I also have my layer of OSB as tight as possible against my walls.
Should I cut back my top layer of sub from the walls where it touches? (Which is most of it.) I have laid 470 sf of it. Yah I know, big project for a first timer.
Hi Tim,
Yes, you need space around the perimeter as well as between the individual sheets. All wood, even osb, expands and contracts. If it’s butted tightly it may expand and ‘peak’ at the seams, which could cause cracked tile and grout. I would also find a new ‘advisor’.
Thanks for this detailed and informative post! I am adding backer board to my kitchen’s wood subfloor in order to install slate tile. The kitchen consists of one area that was part of the original house (built in 1928) and a newer area that was added in the early 1990’s. The old area has a solid wood floor and the new area has 5/8″ plywood, and the transition from the solid wood to the plywood is level. The joists underneath are 16″ on center. The floor does not obviously shift or bow when it is walked on, but the old solid wood has the issues that old wood can have – some knots and irregularities. My question is this: if I have space to add about 1/2″ to the subfloor height, would it be better to add 1/4″ of plywood to the entire surface and use 1/4″ backer board, or would it be better to just use 1/2″ backer board? Thanks again for sharing your knowledge!
Hi Megan,
It would be better to have 1/2″ plywood and ditra.
1/4″ plywood won’t add any significant help to a floor with only 5/8″ base. 1/2″ plywood will help a lot. 1/2 backer add no significant help structurally either. Given your choices, as well as my own choices my preferences in order would be:
1. 1/2″ ply and ditra
2. 3/8″ ply and ditra XL
3. 3/8″ ply and ditra
4. Ditra XL only
5. 1/2″ backer
6. 1/4″ ply and 1/4″ backer
So I guess the answer to your specific question would be number 4 – 1/2″ backer. But the three above it would all be better than that option.
Hey Roger, awesome site!!
I recently started managing a floor covering store so I rely heavily on my
installers for advice and knowledge, especially when it comes to tile. However,
as with any trade, people have developed their own ways or methods of doing things with successful results over the years. To the point; my question is: When it comes to installing backerboard, I have one installer who uses the term “seeding”. I guess he wets his board and then lets it dry before he lays his tile. Or maybe he does it before he sets it in the thinset. Not quite sure on that one.
Anyway,
1) What does seeding mean with regards to tile work?
2) Is it necessary or recommended?
3) Is there any benefit gained, short or long term from doing this.
Thanks for your time!!
Hi Mike,
1. Seeding in regards to backerboard means pre-wetting the board so the interior is saturated. This is done so the backer does not suck moisture out of the thinset prematurely, which weakens it.
2. It is highly recommended, it is technically necessary, but rarely done.
3. A more durable installation, less problems with thinset bond and less chance of not having fully bonded tile to the substrate.
Cement backerboards suck moisture out of everything – quickly. Thinset and other cement products cure through a process called hydration. The process of hydration simply allows for the bond to be stronger the longer it is exposed to water. This is why modified thinsets have latex polymers added to them, to retain the moisture in the cement for a longer period of time, which results in a stronger bond. If the backer is sucking 1/2 of the water out of the thinset you’ll have a considerably weaker bond. If the backer is saturated first (the process is also called SSD – Saturated, Surface Dry) it prevents it from soaking in the moisture from the thinset.
Whoever your installer is you should make sure to keep him around – he knows what he’s doing. Very few are properly trained any more – the above is a significant portion of a properly trained mechanics knowledge. Thanks for the opportunity to get technical for a bit.
Hello
I just read about the “seeding” process and was wondering exactly how to soak the cement board and for how long, including for different thickness. The other questions if this layer needs to dry before installing the tile. Thanks for your help!
Hey Scott,
Long enough so that the next time you soak it the water doesn’t disappear like you threw it on a skillet. Usually three good saturations are sufficient right before you begin setting tile, the face of the backer needs to be dry (or nearly so) before installing thinset onto it.