You want to tile your concrete floor. But there’s a problem. The concrete has cracks in it.
You know that if you tile right over the crack you soon will have a floor tile that’s cracked in the exact same spot. So what can you do to keep the tile from cracking?
Estimated reading time: 3 minutes
Do Uncoupling Membranes Really Prevent Cracked Tile Floors?
Maybe you’ve heard of a floor tile underlayment called uncoupling membranes. You know, products like Ditra or perhaps some of the uncoupling membrane competitors of Ditra.
These products are popular on DIY television and, today, many people are choosing, for example, Ditra over cement board. You may want to read my post on Ditra installation tips.
It’s possible that a store clerk or even a tile professional recommended uncoupling membranes as a way to prevent cracked tiles. Is this good advice?
Uncoupling membranes are designed for movement
In this post, I link to an animation that shows how Ditra will allow the tile layer to move independently of the substrate.
It shows the air pockets created by the geometric shapes in the mat.
But, animation isn’t real life. So, just how much movement are we talking about?
Crack isolation membranes
There’s a classification in the tile industry called crack isolation membranes (CIS membranes). These membranes have undergone particular tests and met certain criteria.
They’ve been scientifically tested in what they can handle and how much they can handle. They will prevent some cracks from transferring through to your tile.
The membranes that have met these requirements are labeled as ANSI 118.12.
The Uncoupling Myth
Uncoupling membranes seem like they would prevent cracks also. But the fact is that most haven’t been (officially) tested as crack isolation membranes.
The powers that be in the tile industry want uncoupling membranes to be their own classification- separate from the CIS membranes. So this means that they will have their own tests.
Certainly uncoupling membranes will stop cracks, right?
Not necessarily. The uncoupling membranes have undergone private unofficial tests.
I’ve heard whispers of some that will pass the crack testing and others that won’t. But until these membranes are required to undergo industry testing we can’t be sure of how they will perform.
For example, Custom’s Redgard uncoupling membrane has been submitted for the A118.12 crack isolation test and passed.
So, not only is it considered an uncoupling membrane but is also categorized as a crack isolation membrane.
How to prevent cracked tile floors?
If you want to prevent cracks in concrete from transferring through to your tile floor the best products on the market are A118.12 crack isolation membranes.
These have been tested and have the highest performance.
Although uncoupling membranes are easily available and it seems like they would prevent cracked tile floors we can’t and shouldn’t assume that they will.
CIS membranes are still the top performers in the tile world.
So, the question isn’t “Do uncoupling membranes prevent cracks?” The question should be “Is my membrane an A118.12 crack isolation membrane?“
Hi again! Do crack isolation membranes provide the same function as uncoupling membranes? I know uncoupling membranes can’t be assumed to have crack isolation properties, but what about vice versa? For instance, since rpm mats meet ansi 118-10, will they be just as “uncoupling” as ditra heat? Thank you!
This subject is a bit of a hornet’s nest because then you get into “what is uncoupling?” There have been many debates on internet forums and even the tile committees that have opined on this uncoupling feature and, more importantly, what the actual benefit is.
So RPM mats will provide a tileable surface. So will Ditra and Ditra-Heat and any of the other uncoupling mats. So will cement board or Hardibacker. Will they “uncouple?” First, we have to figure out what that is and define it.
So far the definition is a mat with a “geometric shape”.
I’m probably not answering your question but it would honestly depend on who you talked to. RPM mat people will tell you the benefits of their mats over the heat membranes. Uncoupling heat membrane people will tell you the benefits of their system over RPM mats.
What I can tell you is that I’ve used both and they both work. When I add up costs and the steps necessary to install I’ve found that I much prefer uncoupling heat membranes.
One thing: I saw the claim of crack isolation on the RPM website but it doesn’t give any details. I would want to know if it achieved that rating with the vinyl glue that the company recommends to install.
It used to be that to install RPM mats over concrete that a urethane adhesive was required. The urethane adhesive was a crack isolation membrane all by itself- whether you installed anything over it, or not.
So is the claim of crack isolation with that adhesive or the vinyl glue? That’s important to know and I don’t know the answer.
edit: upon closer examination, the instructions for going over concrete list the urethane adhesive (Hydroment Ultra-set Advanced). This is a good adhesive if installing over concrete. If you plan on using other adhesives and need a crack isolation membrane then I would try to find out more.
Thank you for all that info, really appreciate the time you take to answer. I’m installing over wood subfloor, so I guess it doesn’t seem like it could decouple as well as ditraheat if it is glued down to the subfloor.
Kim Klein says
Hi – We have some LVT that has issues with the adhesive coming up thru the joints between the tiles. I think one room at least might have to be replaced b/c of it. The house is built on a slab and the LVT just went right over the concrete slab with no membrane or redguard or anything under it. The adhesive tends to ooze up when we’ve had a lot of rain, so I am thinking the water is sort of coming up thru the concrete and causing the problem. This is a long way ’round of asking if an isolation membrane or even redguard would keep this from happening if we replace the LVT and put it down first.
if you have any other thoughts, I would sure appreciate hearing them! Thanks very much – I appreciate your time and help.
I hate to give this as a comment but I really know nothing about LVT and how it’s supposed to be installed.
You might try going to the John Bridge forum and asking this question in the Advice section. It’s a tile forum but there are many installers that do general flooring and not tile specifically that may be able to help with this question.
Sorry I can’t be of more help.
Thank you! I appreciate your prompt reply, and I’ll try over there! Many thanks!
Scott Bauhofer says
I have a 4 year old house with cement slab.
Installing ceramic tile.
Our installer had said we have option of installing ditra (adds a fair amount of cost) but can also go without it
Trying to figure out what to do
I like the idea of adding a membrane over a concrete slab. However, typically concrete will have cracks in it and Ditra is not considered a crack isolation membrane.
I’d rather see a membrane that is actually rated for that purpose such as Nobleseal CIS. It should have a A118.10 stamp on it.
We about a 3000 sq ft of pool deck that has significant cracks and the deck is tied to the concrete coping, movement still occurs will a decoupling membrane still work with the deck still moving.
If you are trying to tile over a crack you’ll want a crack isolation membrane but even they don’t work miracles. Some of them will stretch up to 1/8 inch but if you have vertical movement or significant sideways (in-plane) movement then I don’t think anything can be done.
CIS Membrane or not, that is the question. Durock is installed over a wood floor, screws every 2″ on the seams, every 6″ in the field per recommendation. Floors will have electric heat by Thermosoft taped or hot glued to the Duroc. Then either floor leveling compound or thinset to embed and secure the wire and mesh. Should an uncoupling membrane or CIS membrane be used over the thinset? Large format marble tile will be used to finish. I would prefer less height in this kitchen. Windows are in place and it would be good to have 38″ counter heights.
Opinions on this so far are like family recipes for Gumbo. Thanks, in advance.
It’s not required to add a crack isolation membrane in this situation but I don’t see it being a negative either. Being as most are under 1/16th of an inch thick it won’t make any difference in the height of the floor.
So if you are really an overkill type builder then you could install one over the top. You could also just coat it with a liquid like Redgard.
But I think it’s unnecessary. Also, I’m assuming you’ve staggered the seams on the Durock board, thinset it down, in addition to screws, and taped and mudded the seams with mesh tape.
How many different Crack isolation companies are out there? So in uncoupling membrane is not a crack isolation membrane? Because Schluter says they do have a crack as solation membrane.
Firstly, what I consider a crack isolation membrane is one that has and A118.10 rating. So, just because a membrane is an upcoupling membrane doesn’t mean that it isn’t a crack isolation membrane.
In fact, I know that some are. For example, Custom Building Products Redgard Uncoupling Mat has an A118.10 rating. Additionally, I know, from off-the-record sources that some uncoupling membranes won’t pass the test.
Lastly, I’m not aware of an A118.10 membrane that is manufactured by Schluter but that doesn’t mean that they don’t have one. There are several companies that make crack isolation products and, like anything, some are better than others.
Roger Hodges says
It is painful to read these posts and see you avoid answering what products do have A118.10 certification…
“Lastly, I’m not aware of an A118.10 membrane that is manufactured by Schluter but that doesn’t mean that they don’t have one. There are several companies that make crack isolation products and, like anything, some are better than others.”
I’m not sure what you want? If you have questions about particular products then I’m happy to share what I know. I don’t keep a list of every A118.10 product on the market though. If you want a good one look at Noble Company.
Thomas Sheputa says
Hi! I’m laying 6″ x 24″ ceramic wood-finish tile on my concrete floor (slab). The concrete slab has an expansion joint (or maybe control joint) from the front door to the back door. The long edge of the tiles I’m putting down will be parallel to that joint. I’d prefer to put a tile expansion joint directly over the concrete expansion joint, but the problem is the concrete expansion joint isn’t square. From the front door to the back door, that joint is about 1/2″ off square. So it seems my options are to install the tiles unsquare to the walls but aligned with the concrete expansion joint, or install the tiles square with the walls but not aligned with the joint (so some tiles would go over that joint).
If you are installing directly over the slab then you’re supposed to honor that joint. However, if you use an uncoupling membrane, many of them will let you relocate that joint to a joint in the tile assembly. I would check out the Ditra handbook if you are thinking about going that route.
Peter D. says
I’m using hydronic heating in a 11/2” slab poured over the wood subfloor. The slab has cracked in every direction already. Will it continue to crack and what’s the best method to isolate the cracking to the stab?
If the slab is ok then you can go over it with a A118.10 crack isolation membrane. I like Noble CIS for this but there are other products also.
I install a tile floor over backer board did not use tape ,never had a problem before I have a few stress crack, floor is solid ,what type of membrane could I use to tile over
If you’re looking for an uncoupling membrane to tile over I like Redgard and Flexbone are my personal favorites. But there are others that are good that I haven’t tried, like Stratamat. Additionally, Ditra is always a popular choice.
I need advice. I have a decoupling membrane beneath my kitchen floor tiles, installed around 8 years ago, but over time some of the tiles sound like they are crunching or the adhesive is breaking up beneath the surface. Nothing is moving, not even a single tile, no grout is cracking up, in fact it all seems rock solid. You can’t see any movement at all. But the noise when pressure is applied is definitely there. Short of ripping up the whole floor (only around 10 tiles are affected) is there anything I can do? I had wondered about drilling a tiny holes through the grout down to the membrane and squeezing a silicon in to fill any gaps, or a self levelling compound?
It’s unusual there wouldn’t be any cracking if things are moving. You might try tapping on the tiles and seeing if any of them sound hollow. If they do then that means they are loose and should be fixed.
But if everything feels solid and you don’t have any cracking or moving then I don’t know that I would tear into it just to fix the sound.
We are installing 6″ x 24″ porcelain tile over plywood in a groom shop. I would love to use something like Ardex 8 + 9 which rolls on like paint and in two coats provides complete waterproofing and crack isolation membrane. My question is does that crack isolation membrane also eliminate cracking from being installed on plywood, or does that only protect against cracks in substrate translating to cracks in the tile? The product isI APMO Certified, ANSI A 118.10.
To nitpick the terminology a little bit, a crack-isolation membrane can help prevent a crack from telegraphing through the tile. But it can’t be guaranteed to eliminate all cracking.
The plywood that you are installing tile over should be AC exterior plywood and it should be an underlayment layer that is on top of the subfloor. Not the subfloor itself. But, yes, it can help prevent cracks from forming in the tile in plywood or concrete.
Most cracks from plywood would be from deflection (up & down movement) though and I don’t think it will really help against that sort of an issue.
There is one major manufacturer that offers a crack isolation fluid membrane that is both crack isolation membrane and waterproofing membrane. This one, though offers more than double the maximum crack protection of all membranes like Redgard and Ditra: 1/4″ shrinkage crack protection that exceeds ANSI A118.12. All others only offer 1/8″ crack protection.
This sounds like something a manufacturer would claim and probably isn’t verified by a third party. I’m not 100% sure, but I don’t think the official test measures beyond 1/8-inch. So, other products may also exceed 1/8 inch but they simply don’t advertise it or make the claim.
Darryl Demaray says
I’m removing an engineered wood floor over a concrete slab in a three year old house in a tropical climate. The floor has been glued down and the installer recommends a fracture membrane material although he hasn’t specified what that material will be. It adds a significant expense as 2500 sq ft is involved.
What questions should I be asking the contractor regarding options, cost, installation process for the best results. Thx
The odds that you are going to expose 2500 sq. ft with no cracks in the concrete are basically zero. So, I don’t know what this installer has in mind, but the glue should be removed from the slab. Typically, this is done by grinding the concrete so it’s ready to accept mortar or other adhesives.
A crack-isolation membrane that has an ANSI 118.12 approval on it is definitely a good idea over the whole slab but it’s pretty essential over the cracks. Typically, it’s to be 3x the length of your tile in its width and cover any hairline cracks.
Additionally, there are oftentimes control joints or other types of engineered joints in the concrete that should be honored up through to the tile. The control joints can sometimes be relocated to a nearby grout joint but that, too, requires a membrane. And it’s essential that there is a plan for movement joints in the tile for a floor this big.
So there are a lot of things that hopefully your contractor already knows and is planning for. But, it’s always nice to bring these things up and go over the plan with him or her.
I’m tiling a small bathroom with 12×24” porcelain over concrete slab (1/8” grout spacing). House is 15 years old. The previous ceramic tile has been removed, it was tiled directly to the concrete slab and didn’t present any cracks just a couple loose tiles (perhaps caused because tile was incorrectly installed against baseboards using grout so zero expansion gap). The thinset was mostly on the backs of the ceramic tiles (not the floor) when removed. The concrete substrate is smooth, and will absorb water after several minutes (seems to take 10-20 to absorb drops), so I am concerned about contaminants on the substrate hindering the thinset bond (using Versabond LFT). My plan is to use Custom’s cement patching compound to address a couple small cracks, then apply Custom’s Multi-surface bonding primer on the entire substrate (which will add equivalent to 80 grit texture to the surface), then thinset and tile on top of that. I’ve read a lot on uncoupling membranes, but I’m not sure if I need to use one – especially knowing that the crack prevention/isolation membranes won’t necessarily do their job guaranteed, and the crack issues seem very minor …and the Redgard mat from product reviews seems notorious for crumbling grout. I also don’t want to use unmodified thinset since I’m working with large format tiles, so that rules out Ditra mat. Also, since porcelain doesn’t absorb much water, I was thinking waterproofing a concrete substrate is unnecessary. How would you handle this substrate and tile job? Am I approaching this job well enough to make the tile installation work well? Any suggestions?
Now I’m thinking I should use custom’s Megalite ultimate Crack prevention LFT mortar instead – it specifically lists cement treated with the Multisurface bonding primer as a suitable substrate…
The MBP should be fine to make it so you can adhere to the surface. But to help manage the crack, I don’t think the patching compound is the product that you want. You could use Redgard uncoupling mat which I think is a nice product for LFT tiles. It’s also an A118.12 crack isolation membrane. However, you could use Redgard in the liquid version also.
From there, I think you’d be fine with a mortar such as Versabond LFT but Megalite is (over) qualified also.