There are three basic materials used to set tile.
- Mastic
- Thinset Mortar
- Epoxy
For each installation there is a specific material you should be using. Before you start any tile installation you should ensure that the material you choose is suitable for that application.
Mastic
Mastic is a latex or solvent based adhesive that cures by evaporation. It is sold in airtight containers (buckets) and requires no mixing. It is ready to use immediately. It is suitable only for non-wet applications.
Mastic should never be used for showers or floors! Ever! When mastic gets wet the water will re-emulsify the adhesive base. This means that mastic turns to goo when it gets wet. Goo will not keep your tiles on the wall. Every one of the failed showers that I’ve ever replaced were installed with mastic.
With that said typed, mastic does have its place. It is “stickier” than thinset mortar which is why some prefer to use it – for everything. It should only be used in non-wet areas such as a backsplash, wainscot, or fireplace. An area that is not consistently exposed to water or moisture. It should also only be used on tiles smaller than 6 inches square.
Think about it like this: mastic is stored in a bucket with a lid on it. This keeps it from being exposed to air which would cause it to cure (dry). If you spread it on your wall and place a 12 X 12 inch tile on it, that’s just like putting the lid back on the bucket. It will never fully cure. If any moisture gets behind that tile with the mastic it will eventually re-emulsify and lose adhesion. That means is that your tile is going to fall off the wall.
There is also a product called “premixed thinset adhesive”. This product is pushed as a suitable material with which to set tile – it is not. It is only mastic with sand added to it. While sand does help materials from shrinking as it sets, it does not make mastic suitable for showers or floors.
Thinset Mortar
Thinset mortar is what you need to use for shower walls and floors of any type. It is sold in bags and needs to be mixed with water. Sound simple? It is. Referred to as thinset, mud, mortar, or a number of other things, it is a combination of sand, portland cement, lime, and other stuff that makes it the preferred setting material for elves everywhere.
When mixed properly (read the directions, no, really, read the directions) it is stable, not compromised by water or moisture, and rock solid. Thinset must be mixed with water, allowed to slake, then remixed before use. Slaking refers to letting it set for a specific amount of time to allow the chemicals to interact and become workable.
Thinset cures through a chemical process, not by evaporation. Air is not required for it to set. It will cure in the bottom of a bucket of water, really. This means that no matter the density or type of tile you use it for, it will fully cure. No worries there. The tile will stay where you put it.
Unlike mastic, thinset will not be compromised by water or moisture. If it gets wets the thinset will remain cured and will not be reactivated. It’s similar to your driveway. The concrete on your driveway was mixed with water but it doesn’t turn to mush when it rains. It’s the same stuff.
Thinset mortar will be the correct setting material for nearly every application.
Epoxy
Epoxy is a chemical based glue that cures through chemical interaction. It is almost bulletproof and not user-friendly. To be frank, it’s a pain in the ass. It is usually a two or three part product which, when mixed together, form a very stiff, very thick putty-like substance. When cured it becomes a permanant part of whatever is attached to it. That’s great on the back of the tile, not so much if you get it on the front. Use with care, it is nearly impossible to get off of anything once it’s set.
There are not many applications which require the use of epoxy setting materials. Certain exterior applications need it, swimming pools, certain types of stone and glass tiles. While epoxy can be used for any application, only specific jobs actually require it. It’s expensive. I mean really expensive. If you don’t need to use it, don’t.
If you are unsure whether or not your product or application requires epoxy, just check the manufacturer’s recommendations. If it is required, they will make sure you know about it. You can also ask me, just leave a question in the comments. I’ll reply, I’m a fairly sociable guy when I’m not crawling around on a floor.
Which to use
The general rule of thumb is to use thinset mortar. Unless your specific application requires epoxy, thinset can be used. Anywhere you can use mastic you can use thinset instead. It is more durable, water resistant, and cheaper than mastic anyway. As far as I’m concerned, the only thing mastic is good for is a free bucket.
Kari… If roger doesn’t reply in the time you require, email me at 081manager@tileshop.com
I can help.
Joel
dj… Yes, epoxy backed tiles require a special 2 part thinset sometimes called epoxy. Where are you located? I may be able to direct you to a place to get the right stuff.
Joel
I am in the DC area. However I’ve had one person take a look at the installation and I’ve decided to leave it installed with the thinset. It is very solid now, I just hope it stays that way. also, I checked the back of the tiles and there are areas on each mosaic tile where the resin doesn’t cover so I’m hoping there is enough direct stone to thinset contact. Thanks for your help.
DJ
Hi Roger,
My name is Joel, and I’m the manager of a high end tile store…. Been in the industry 20 years, 10 of which as a contractor.
I just wanted to make one correction to your post (great post btw… I’ll be saving it to show customers/old school contractors why they should not be using mastic)
There are 2 types of thinset mortar. Modified and unmodified. Modified has latex (actually any number of chemicals we incorrectly refer to as latex, but that’s a convo for another time) while unmodified does not. Your statement about thinset drying underwater (without air) is partially accurate. Only unmodified thinset will dry without air. Modified thinset, which is the dominant thinset in the industry currently, needs air to dry. This is why Schluter requires the use of unmodified thinset in their shower systems… Because their system is air tight, and the tile going on top of it is air tight. Modified thinset will only cure through the air it is getting through the grout joints, which takes a long time, if ever, to fully cure.
Again, great article.
Joel
Thank you Joel, I’m aware of the differences. I try not to overwhelm my typical readers with too many specifics, just enough to get the point across. You and I are not the typical diy’er, though.
Thank you, I do like knowing people in your position do know the difference, though.
Hi Roger,
I hope you don’t think I was questioning your knowledge on this, as that was not my intent, and I agree that us spending a lifetime in the industry makes us a little different than the typical do it yourselfer. The main reason for my comment was that, even for first time DIY’s, the difference in the two types of common thinsets is becoming more and more relevant, especially with the growing popularity of Schluters Kerdi and Ditra systems (which personally I’m not a fan, but that doesn’t mean they still aren’t gaining popularity).
So please don’t think it was an attempt to undermine your knowledge on the issue. As I believe I stated earlier, I was so impressed with the article as a whole, I’ll be using the mastic portion of it for training employees, educating DIY’s, and even the “old school, stuck in their ways” tile setters.
Keep up the good work!
Joel
Hey Joel,
I didn’t think that at all. I appreciate the discourse – it’s how we learn.
Thank you.
Hi Roger
I am tiling my bathroom floor with marble tile attached to 1’x1′ mesh sheets (may be resin backed). I used Mapei’s Ultraflex 2 modified thinset since that is what the tile store sold me with the tile. Now I just read Mapei’s fine print and it says not to use with resin backed tile. But as I’m finding out, there seems to be conflicting opinions on everything in the tile world.
Should I remove the tile and use an epoxy instead? The tile seems to be solidly attached to the floor right now. Will I have problems long term?
Thanks for your help!
DJ
Hi DJ,
Although most mesh 1×1 mosaics do have some sort of resin on the back, there are still open spaces for the mortar to bond to the tile itself. Depending on how much resin is on the back of the sheet will determine the overall bond strength of the mortar. Some sheets have only enough to bond the tile to the mesh (correct) whereas some are absolutely slathered with resin, which will not bond well long-term with thinset.
Hi Mister Elf!
Thank you for the great (and sometimes funny) info! I’m getting worn out trying to find answers on the web and hope you can help. I’m laying 6×24 porcelain over 1254 sq ft of concrete, most of which had engineered hardwood glued down by Superman that I am in the agonizing process of removing.
1. Which is better: Mapei’s Rapid Setting or Mapei’s Porcelain mortar?
2. How highly do you recommend using Ditra? That would be hugely costly for me. Is it worth it?
4. Do you recommend RedGard with FlexBond instead of Ditra?
5. How perfectly do I need to remove the adhesive from the concrete before using any of the above products? The floor scraper gets it down smooth, but it’s still there in a lot of places. I fear only kryptonite will work.
6. I have a large settlement crack running through the family room 1/4″ wide. The house is 5 and a half years old in Georgia. What do you recommend for that?
7. Should I give up DIY and spend the rest of my days lying on the sofa?
Thank you in advance!!
Kari
Correction: 6×36
See – you do have something against the number three!
Hi Kari,
1. The porcelain mortar, rapid set is exactly what it says – rapid. You don’t need it unless you are under a time constraint – like a 24 hour one.
2. Yes, it is worth it in my opinion. It’s not nearly as costly as replacing the entire installation is something goes wrong that the ditra could have prevented.
3. There is no number three. I’m not sure what you have against the number three – but let’s try to keep it orderly here, yes?
4. That will work as well, but redgard has no vapor dissipation abilities, only vapor blocking (to an extent).
5. Until water soaks into the concrete within one minute when splashed onto it.
6. You need to have a soft joint over the top of it, and it would be best to have additional crack suppression over the entire floor to prevent further issues – both ditra and redgard do that.
7. Probably. But then, I probably should as well.
Hi Mark,
I am applying porcelain tiles to steel stair nosing, is there a product that will adhere these as it is a high traffic area. there will be a tile edge on the tread so the top of the nosing will be covered.
Thanks
Hi Chris,
Not that I am aware of, but give the tech department at Laticrete a call, I’m sure they have something that will work for you.
Hi. I’m trying to help a client fix a problem and need help. Shower floor is kerdi. She wants glass 1x1s on 12×12 mesh sheets. Warranty aside will the tile stick with unmodified thinset used? And if yes what about the grout? Is urethane grout bad ideafor shower floor? Thanks. I Enjoy your site.
Hi Pam,
It likely won’t bond long-term. Just use modified thinset. Urethane is fine for the floor provided the cure time is followed before water exposure.
Hi Mark! Thanks for your time with all of these questions! We had some porcelain tile picked out for our shower, but made a last minute decision and switched to ceramic. I’d already purchased Mapei Porcelain thin set, and completely forgot to switch it to Ceramic Thin Set. The project is finished. What should I expect to happen?
Thanks,
Brent
Hi Brent,
It will be just fine.
I recently used the mastic mortar on the shower floor to level off some spots. Now, after reading your comments I found out it’s the wrong thing to do. What should my next step be?
Hi Todd,
You need to scrape that stuff out and use regular thinset – the powdered stuff in a bag you mix with water.
Hi there
I recently tiled a small area of floor- 12X24 porcelain tile. I used a pre-mixed thin set. it has been a week and it looks like the thin set may still be wet in areas. After researching a bit (still pretty new to this) I realize the use of the pre-mixed thin set is a mistake. any suggestions….
Hi Marc,
Yes, remove the tile, scrape the mastic off of it and reset them with thinset. If you have trouble getting it off the tile just soak them in water.
Good Morning Roger,
Using 12×24 porcelain tiles on shower walls and floors. I have used Hardie backer board on both (1/2″) and applied Mapei waterproofing to the shower walls and certain areas of the floor(near the planned shower door and tub). First question: Do I need to prep the areas with Mapei prior to thinset application? Second question: I have been reading lots on a medium bed mortar/thinset being used for showers and floors because of the larger tile. Located a medium thinset for the floor but am having issues with locating something for the walls. The medium mortar for the floors was specific “for floors only”. Any suggestions? Is it highly advisable to stick with the medium based thinsets for both? Last one: Found a trowel guide showing different trowels for tile size. Recommended type for the 12×24 was a 1/2″ trowel….What ya think? Thanks for your time!!
Bill
Hi Bill,
No need to prep, thinset and tile goes directly over it. Any medium bed mortar can be used on the walls as well, whether or not it says ‘for floors only’. I’m betting the same company also has a ‘for walls only’ thinset.
Marketing BS. Medium bed is normally best for large format tile. 1/2″ is pretty large, a 3/8″ should be sufficient.
Roger,
Great site!
I have a little mastic left over and acouple nicks on the wall, (with no drywall mud); could I use the left over mastic and sand when dry?
Hi Mike,
You can fill the holes with it if you want, but it likely won’t sand very easily. It may, I’ve honestly never tried it.
Hello Mark,
Glad I found this site.
I’ve tiled dozens of areas with all types of tile, always used thinset with satisfactory results. Recently I used some Sturdi-flex latex modified thinset to set ceramic tiles on 80-yr old basement stairs constructed of 2x10s. (Previously I had successfully used this mortar for 12×12 porcelain tiles over a concrete floor.) Two weeks later the tiles are lifting off the steps easily, the mortar is still wet in spots, and it scrapes off pretty readily upon soaking the tiles. I thought thinset couldn’t be dissolved. Am I expecting too much of this mortar? What can I use instead to re-set the tiles?
Thanks!
Hi Carol,
Did you set the tile directly to the wood? If so, that is your problem. I don’t know why it is wet, but the movement of the wood (regular expansion and contraction) will ‘sand’ the thinset away and cause your tile to debond. You need to have a proper substrate beneath your tile like cement backerboard or ditra.
Based on an earlier response, would the large format tile thin set be the correct choice for the floor under the 12×24 porcelain tiles? thanks in advance.
Hi David,
Yes, a medium-bed mortar (also called large format tile mortar).
Long time since my last question. Kitchen floor, slab on grade, reasonable flat (0/-1/4″). Plan on using 1×2 porcelain tile. Is Mapei Porcelain Tile Morter the correct setting material? If yes, I was planning on 1/2 x 1/2 trowel and would this be correct given the 1/4 variation in the floor. thanks in advance. The last 3 bathroom projects you advised on came out wonderfully. – Dave
Hi David,
Yes – to all your questions.
Mapei’s porcelain mortar is great stuff!
? I have floated my entire floor with unmodified thinset, we installed ditra heat cable over their product so to protect the cable. I floated the entire floor with unmodified thinset. My question is, with that being said, can I use modified thinset over the cured unmodified thinset to set porcelain floor tile?
Hi Ralph,
You can, but you’ll lose your schluter warranty. But yes, it will work just fine.
Can i use versabond to install tile to a “tileredi” pan? I dont want to mess with epoxy !
Hi Lyn
NO. If using a tile redi pan you HAVE to use the epoxy, it’s the only thing that will bond to it and last.
My daughter bought a home about 6 weeks ago. The bathroom had some tiles that were starting to pop off right above one edge of the bathtub. The previous owners re-plumbed the tub with a shower (chrome pipe going to shower head from the tub spigot). I told her I would help fix it. The tiles are metal (steel, I assume). They are mounted to what looks like a fiber board with a gridwork cut into it. Your site has been so helpful before so I checked it out to find out what type adhesive I should use to re-install the tiles. I’m pretty sure they were installed with a mastic adhesive (the old adhesive is kind of amber in color and semi-transparent). I assume my daughter should abandon using this tub as a shower. Do I have any alternatives that would make this area acceptable for a “shower stall”? Thank you!
Hi Jim,
Unless the backer has plastic or tar paper behind it (you should be able to see this if you pull off the control cover (escutcheon) and looking behind it) you’ll need to waterproof the interior walls. That, of course, requires removing all the tile. You may be able to get away with pulling off a couple of feet and using something like redgard to waterproof the walls, then reinstalling the tile. That will work for a few years. The bottom of the walls is where the moisture collects, so it will be fine for a while. As long as you know that’s not a permanent solution.
Hi;
Great info and resource!
I’m tiling 3 shower walls with 6″ x 24″ porcelain tiles. Substrate is Hardie boards coated with RedGuard. I’ve read about special “LFT” (large format tile) thin set from Mapei and others.
Do I need the LFT thin set for these tiles on walls, or will the regular Mapei modified thinset be sufficient to work with?
Thanks!
Jon in Chicago
Hi Jon,
Regular modified thinset will work fine. LFT prevents shrinking beneath large tiles when placed on floors. It does the same on walls, but in your case it’s not really needed.
I plan to tile over existing 4×4 tile (glossy/slippery) on a shower floor with 1×1/12×12 (much easier than breaking existing tile out). Should I use epoxy to ensure a good bond or will thinset be sufficient?
Hi Jack,
Neither until you scarify the surface of the existing tile and figure out how to deal with your drain. Once you do that you can use epoxy or a thinset approved for installation of tile over existing tile.
Hi Roger,
Installing porcelain shower tile over Kerdi. Schluter says all applications should use unmodified thinset for both Kerdi to backer board and tile to Kerdi. But Mapei unmodified says that thiset must be modified for porcelain tile application.
What do you say?
Greg
Hi Greg,
Welcome to my world.
The TCNA requires modified thinset with porcelain. HOWEVER, the TCNA also says that manufacturer recommendations trump their standards, in other words, technically you should use unmodified.
Hi Mark,
We are tiling bathtub shower surround with tile size 12 x 24″. What type of mortar should be used?
Hi Michaelene,
It depends on what your tile substrate and waterproofing method is. Most of the time a good modified mortar works just fine.
Hey Roger, I am planning to tile my laundry, guest and master bath with a porcelain rectangular 6 x 24 tile. My substrate is 5/8″ mdf (35 yr. old but appears to be in OK condition) W joists on 11″ centers. I have been recommended Schulter Ditra underlayment. Would you rip out the mdf and replace with 3/4 ply? or go over what is there. What thinset would you recommend? Thanks,
-Mark
Hi Mark,
Absolutely I would remove the mdf! No question. I like laticrete 252 under ditra over ply and 317 for the tile over ditra.
Hi,
Great site!
I’m re-doing a shower floor. The tiles are all removed and I’m in the process of taking off the old thinset (which may actually be mastic). There are some divots in the mortar, as well as a crack or two. Can I count on the new thinset to fill those?
Thanks!
Mark
Hey Mark,
Yes, provided your substrate is sturdy you can go right over those with thinset as you are installing your tile.
Hello Roger,
Always look to you for tile questions – you are honest, direct and knowledgeable. Setting large format porcelain tiles (17 3/4 x 35 1/2) on fireplace wall. Any advice on thinset mortar – actual brand and type. As well, any ‘best practice’ tips for these large tiles. Many thanks
Hi Doug,
Any good modified mortar will work just fine. Laticrete 254, mapei ultraflex 2 or even customs versabond will work fine. Just make sure you get good coverage, pull one or two off after you install them to ensure you are getting a good bond.