Cement board installation is not something that is incredibly difficult.
I think most people worry about how to cut it and once they have a plan for that then they think it’ll be a breeze.
But I’ve seen these screw-ups for several years now. It’s the same ones over and over.
Which products are we talking about?
Mainly, the products I’m talking about are considered to be cement backer boards for tile installation.
These come in two categories: cement board and fiber cement board.
Examples of cement board are: Wonderboard, Durock, and Permabase
Examples of fiber cement board: Hardibacker and Fiberock,
Let me throw in one disclaimer here: These are general guidelines. Each manufacturer will have their own instructions for their own products and they will vary a little bit from each other.
So the moral of this story is to read the instructions and not simply this post.
Messing up cement board installation is not just limited to these 5 ways
Now there are more ways to screw things up than just these five things. In fact, this is already assuming that your wood subfloor meets the minimum requirements.
Hint: cement board should never be counted on to stiffen up your floor. The floor needs to meet minimum requirements for tile BEFORE any tile backer board is installed.
However, these are the five that stood out in my unofficial memory as being the most common.
Here they are:
1. No Thinset underneath the backer board
Just the other day, I saw a video featuring someone fastening Hardibacker directly to the subfloor with nothing underneath it. I scrolled down to look at the comments and they did not disappoint. What were his replies, you ask?
“The thinset goes ON TOP of the cement board to stick the tiles!”
A simple perusing of the instructions would show otherwise. But most people don’t look at them- not even the pictures.
Also, I know some are wondering but, no, Liquid Nails does not count as a thinset replacement. We have to remember that this isn’t the same as installing plywood. Cement board is a different product and it needs to be installed in its own way.
Additionally, screws don’t take the place of thinset either. I talk more about screws in #3.
Which type of thinset do I need for underneath the cement board installation?
Here’s the bit of good news: it doesn’t really matter which brand or type that you purchase. I know the manufacturers will want you to use their own brand and may even specify a type. If so, then you should purchase what they require.
But the system works by having a bed of mortar underneath holding the board up and fasteners from above holding the board down. You don’t need any fancy mortar to accomplish that task.
2. Not Staggering the Seams
Now, this is an area that the plywood installers will be familiar with. You don’t want four cement board corners to all come together in one intersection.
You get around this by staggering the boards during installation. One nice thing about tile backer board is that it doesn’t matter which way that you run the sheets.
You can run them one direction or another but as long as the corners don’t all come together it’s OK. Additionally, you don’t want the cement board seams to line up with the subfloor seams.
Those are the two things to watch out for with cement board installation.
3. Fasteners
Most cement board manufacturers require galvanized roofing nails or cement board screws.
But this doesn’t stop people from trying to use ring shank nails, drywall screws, or who knows what else?
The problem is that those fasteners don’t have the holding power that cement board screws and roofing nails have.
Additionally, people also mess up fasteners by not using enough of them and driving them too deep.
Typically, it’s every 8 inches throughout but there is some variation between brands on that. Some backer boards will have the fastener locations printed on the board.
4. Not using Mesh Tape on the Seams of your Cement Board Installation
This is more of a little known fact but most cement board manufacturers want fiberglass alkaline-resistant mesh tape embedded in thinset mortar over the backer board seams.
Mesh Tape: Don’t Skip this Step
I remember a time when this wasn’t a requirement but it has been required for the last several years.
5. Installing cement board over a concrete subfloor
If you have a concrete subfloor then you should not be contemplating installing cement board over it.
I know it seems like a smooth surface and it seems like it may fix some of the issues with the concrete floor but don’t do it.
Not only is thinset a critical component underneath cement board but the other critical component is the fasteners. And you won’t have the fasteners if you are trying to install it over concrete.
On the bright side, there are some options for concrete subfloors. One of which is self-leveling underlayment and other floor flattening products.
The other is foam backer board which is OK to install over concrete. This can be beneficial if you are wanting to insulate concrete from an electric floor heating system above it.
Check with Wedi, Schluter, Laticrete, GoBoard, or whichever manufacturer to see how they want their product installed over a concrete subfloor.
Honorable mention
I know, there are more ways to screw up cement board installation than just these five.
I could list wrong trowel size, thinset mixed too thick, thinset allowed to skin over, and others.
You tell me in the comments: which ones am I missing? Which mistakes do you see?
Helena says
The guys are coming on Monday to install porcelain wood looking plank tiles – size 6×36. He asked if I wanted a staggered layout with 3 different sizes.. does that mean he will cut down the tile, if so, is that the correct approach? I don’t want small (say 12 & 24 inch pieces of planks staggered unless it’s in the beginning of a row) I would prefer all full size planks.
I read the 33% approach and I’m confused what that means. Does it means you stagger a 1/3 in random patterns without cutting the tile? If I want all the tiles to be 6×36 in a random pattern, what do I ask for? I do understand that some tiles will need to be cut in the beginning and end of the rows. I’m sorry this seems so simple, but I am so confused 😩. Thanks so much, H
DIYTileGuy says
It can be done without cutting the lengths of the tile in the middle of the floor. A random stagger just means that they will offset each row up to 1/3rd of a tile (or 12 inches). So your offset can be 4-12 inches and varying on each row and still be under the 1/3 recommendation.
Handyman Morris says
I would say always be very careful when working on any type of floor in your home. I’ve worked with many tile floors and let me tell you, when I first started out doing tile layout and home remodeling, on my own house of course, I screwed up multiple times. I hate to admit it. But once you develop the skills and patience to do this type of remodelling it really isn’t too difficult. Just a little pro tip though, if you are going to try and remodel your floor or tile, please do yourself a favor and buy extra tiles. About 20% more. Just in case you mess up and need extra tiles to cover your mistake. And of course, if someone doesn’t feel comfortable with doing any type of work on their home, you can always call a professional. Call either a contractor or a Handyman. Make sure they have a good reputation, and they are charging honest fair prices. Shop around a little to make sure you are getting someone that is best qualified for the job.
Joe says
So I am converting a walk in closet into a bathroom in my main bedroom. While on vacation, I had a plumber come over and do all of the piping and my friends and I were going to do the rest. The plumber had called me and asked if I wanted him put up greenboard while he was there, for more money than I should have allowed, but I went along with it and said yes.
When we got home, we saw that he put greenboard all the way around the room, including where the shower will go. My limited knowledge of showers is that you do not want to tile over greenboard. He had said he has been doing it for 30 years and still does it at the apartment community that he contracts for, and has never had or seen an issue. My thought was to cut out the greenboard and attach durock directly to the studs.. My lovely girlfriend thought it was stupid to rip out part of what we just paid for, and to avoid the argument I decided we could just put durock over the greenboard.. Research has conflicting answers on whether this is acceptable or not. (Mind you I had to cut out pieces of the greenboard prior to putting up the durock because there wasnt a stud where the door needed to connect so I installed those).
Now that the durock is up, I thin set, mesh taped, and then thinsetted again over the seems and also thinset over all screw holes. I applied 3 coats of redgard over everything and am ready to tile this weekend. Though I am kinda at the point of no return with some of this, here are some general questions that I have:
1. is putting durock over the greenboard really a big deal? Especially since I have redgard over the durock now. In theory, water should not be able to get through tile and grout, through redgard, through durock and into the greenboard for mold, correct?
2. I realize now that most of the durock was attached through the greenboard and into the stud using 2 1/4 inch rock on screws but one sheet was put on mostly with 1 5/8 backer on screws… The guy who helped me said 1 5/8 should be okay (1 5/8 going through 1/2 durock + 1/2 greenboard = only 5/8s going into a stud) It all seems sturdy but was this a big mistake? As in is it bad to use backer on screws over durock and do you think the 1 5/8 screws into this will hold up? I applioed screws every 8 inches and it does feel sturdy.
Again, i am at the point of no return but i guess i either want to feel better with a “it will be okay answer” or know that i possibly will have a mess on my hands 5-10 years down the road of 2 months in when the 1 5/8 screws fall out…
Thank you for your help, I apologize for the novel.
DIYTileGuy says
I’m not sure why the green board wasn’t removed in the shower area but I don’t think it will be an imminent failure if durock is installed over the top. I would certainly want the longer screws and you could still add them and Redgard over them with little disturbance to the whole project.
Tim says
Totally agree. Shouldn’t have any issues. Been ruling for 23 years and am always a student of the work. I do a lot of shower job. You should have any issues. Yes over kill but I always put 2 coats of Red Guard on the cement board. Yet I also feel the Cement board doesn’t have enough rough texture to it and feel I can literally peel the Red Guard off the surface of the Durorock. Makes me worry a little.
Julie Chambers says
Hi there I am tiling my mudroom and I have a built in bench with drawers leaving only about an 8 inch gap between the bottom shelf and the floor. The space goes back to the wall about 20 inches. I am trying put hardibacker in and realized there is absolutely no way to get my drill back 20in with only 8in clearance. There will never be foot traffic back there, it won’t even be seen. To do it right tile does need to go all the way back. Can I just use thinset to secure the hardibacker and no screws?
DIYTileGuy says
If that area gets tile then I would try to get some sort of fasteners back there. You might try heavily tilting the drill and driving a couple of screws in at severe angles. It’s not really the right way but it’s about the only way you’ll get anything in there. Otherwise, just do the best you can. That’s all that you can do.
Chad says
Doesn’t a moisture barrier need to be between the cement backboard and floor. The cement will be fine with water but wouldn’t the wood underneath rot? If so, how do you put thin set mortar mix down with the moisture barrier in place?
DIYTileGuy says
No, a moisture barrier isn’t necessary as it’s not expected that floor would see the amount of water that would warrant a barrier or some sort. Typically, that’s only in showers or exterior applications.
However, you could apply a waterproof membrane over the cement board and use a waterproof seam tape on the seams andaround the edges if you were trying to protect it. But unless there is a way to drain water then the water would simply run out the door.
John says
I am doing the tile for my master bathroom which is about 18ft wide and 12ft deep. After mixing the mortar I couldn’t find my 1/4 Inch trowel so I just used my 1/2 inch for 3 of the backer boards. I only got 3 backer boards down with one bag of mortar, then I found my 1/4 trowel. Could I use the 1/4 inch for the rest of the backer board or would there be too much elevation change between the backer on the 1/2 inches troweled thinset? Should I do the rest with 1/2 inch, or should I rip up what I already did (which would be a pain). Thanks
DIYTileGuy says
You’ll run into an elevation change by switching trowels. I’d probably just keep going with the bigger trowel at this point.
George says
I have a wood pine floor can I put tyvek on it then put leveling cement on top of it before I put the hardibacker down?
DIYTileGuy says
Negative. I’m assuming the pine floor is a finished floor? If so, it’ll have to come out and you need to get down to the subfloor. From there you can use Ardex Liquid Backer Board or Custom Building Products LevelQuik fiber-reinforced self-leveling. Or simply install cement board or hardibacker.
Marty Witzel says
You made a comment about putting the fasteners screws in too deep? can you explain that? Should they be flush? Do we also want to be careful they aren’t too high?
DIYTileGuy says
The fasteners should be flush with the surface or even slightly lower. With cement board, screws lose holding power when the head drives below the reinforced surface. Too high is an issue, also, but it happens more with fiber cement products such as Hardibacker.