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 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 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.

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  • Evan

    Hi Roger, I live in a pre war apartment with 2 bathrooms. One bathroom was gut reno’d by a GC. It came out ok but was very expensive. We took out the tub and removed all of the tile for replacement. I plan to Reno the other BR on my own. I’m handy, so I think. I will not remove any tile or the tub but will install a bath fitter tub and use an epoxy adhesive over the existing tile. The tile is fairly level, with no evidence of falling off the wall. There’s also no visible mold. What are you’re thoughts on this and what steps should I take for a primer coat or recommended epoxy? Also, I plan to install 3×6 tile on the walls. The bath fitter will only be for the tub itself.

    • Roger

      Hi Evan,

      I have no idea – seriously. The only thing I know about bathfitter’s products is that I don’t like them – they cover up tile. It is a cheap alternative to a tiled shower. I would check with the company for their recommended installation procedure for their product.

  • Dennis

    Hi Roger,

    I’m tiling a tub surround. Should I use Versabond or Omnigrip. Everyone at Home Depot suggests Omnigrip because I’m tiling walls. They say that Versabond is only used for floor tiles because it doesn’t have the adhesiveness to hold tile on a wall. What’s your opinion?

    • Roger

      Hi Dennis,

      My opinion is that they have no idea what the hell they’re talking about. Use versabond.

  • Trevor

    I’m tiling a shower and would like to know the best thinset for the shower floor. I’m using A 2″ marble mosaic on A red guard shower pan. Preferably something from lowes.

    • Roger

      Hi Trevor,

      Mapei ultraflex 2.

  • dale livingston

    Question, I have a nasty old shower in the basement. Actually the tile walls are in good shape, and the shower floor isn’t cracked or anything it’s just ugly. Can I tile over the shower floor?

    • Roger

      Hi Dale,

      You can, but you’ll need to extend the drain to reach the new tile.

  • Dennis Buchovecky

    Roger, I am planning to install a new tile shower and have been researching different types of systems. I’m leaning towards the Schluter Shower System (Kerdi shower tray, Kerdi drain, Kerdi Curb, Kerdi over Hardi backer on walls, etc.) Schluter recommends using unmodified thinset mortar to adhere Kerdi membrane on walls and floor. I think this should be fine for adhering the membrane. However, they also recommend using unmodified thinset for the tile. I will be setting natural stone tile (most likely marble). In the past, I have always used high quality modified thinset.

    – Have you used the Kerdi system?
    – What do you think about it?
    – Why can’t modified thinset be used over the Kerdi membrane?


    • Roger

      Hi Dennis,

      95% of my projects are built with schluter products. I absolutely love it. Modified thinset CAN be used over it, but you’ll lose your warranty. The issue is that modifiers in modified thinset require air to fully cure. Schluter being a vaporproof (to an extent) barrier limits the amount of air that can get to spaces like the center of tiles. It simply takes a LONG time to fully cure, it could take up to 90 days. Unmodified thinset cure through hydration, utilizing only the water to fully cure, no air required. Either will actually work just fine over schluter for your marble.

  • kelly lafee

    I need to re-apply about 40 pools tile near my spa spillway (1/3 are off and balance surrounding will soon be). In past I have used epoxy for replacement of a few and prefer not to try on a larger scale i.e. it is challenging to work with and tiles still fell off (product or me?). Can thinset mortar work succesfully in this application? Thanks.

    • Roger

      Hi Kelly,

      I assume your substrate is either concrete or a concrete render? If so then yes, thinset will work just fine. On certain applications epoxy will not last long-term unless a very specific installation method is adhered to – this may be the issue with your previous repairs.

  • Jerry

    I’m doing 12×24 porcelain in my kitchen using ditra membrane, I have a plywood underlay with a 4×4 area which I poured SLC. Ditra calls for modified over wood and unmodified over SLC. Pro Flex claims it adhears to both, whats your opinion?

    • Roger

      Hi Jerry,

      I would use modified for all of it. Yes, it will bond to both substrates. The requirement has nothing to do with bond and everything to do with cure time.

  • Camo

    From the comments I’ve read on Home Depot’s sire, I see people use OnmiGrip or AcrylicPro for tile installation on the floor. Some say it’s the best thing ever, others hate it. Are these products really a no-no or OK for a small tile job, like replacing broken tile for example?

    • Roger

      Hi Camo,

      It is not okay for anything that gets any type of foot traffic. Mastic simply does not have any considerable compressive strength and it will eventually fail. People who think it’s the greatest thing ever are too lazy to mix thinset. :D

  • Kat

    We are laying floor tiles that have little squares on the underside. Do these squares have to be completely filled once it is pressed down or is it okay if the thinset doesn’t completely fill the squares? One of us says it doesn’t matter, the other says it won’t create an airtight seal and should be filled. Who is correct? And, can tiles pop up from air trapped underneath? Waiting for your answer before finishing. Thanks!

    • Roger

      Hi Kat,

      You need to back-butter the tile. That means taking the flat side of the trowel and forcing a thin layer of thinset over the entire back side of the tile. This ensures that the pores in the back of the tile are filled so you get the strongest bond possible.

      And yes, that means the little squares get filled. :D

  • KD

    Shower made of “cultured marble”, (what is that acrylic? Is there a good way to tile over that or is the best bet to tear it out?

    • Roger

      Hi KD,

      Yes, it is acrylic. It needs to be removed.

      • KD

        Thank you for your speedy reply!

  • Tony

    I will be using shower base from tile reddi, that came with epoxy for setting tile to the pan. Is it neccesary to use this or can I use thinset with equal results
    thanks, Tony

    • Roger

      Hi Tony,

      You have to use the epoxy. Thinset will not bond adequately to the pan.

  • Spencer severson

    I planned tile in the entryway to my wifes studio up to 3/4″ maple. Planned hardyback over the 3/4″ ply subfloor. Now she wants to use stones, keys, random tiles. There will be varying thickness and odd grout sizes. Use the hardyback? Skip it for more thinset? Worried about cracking, breaking. I framed 1′ centers in the area to have stronger floor for tile. Would epoxy grout be stronger? Too hard to work with? Sure would appreciate advice. Spencer

    • Roger

      You should use the backer. You need a proper substrate beneath any type of tile you do. Give her tile choice you can not guarantee that it will end up flush with the wood, or even with each other tile. Sometimes sacrifices must be made given a certain product selection, so if she is set on that let her know the downsides and at least have a proper installation method in place beneath it. Epoxy is more durable, but it won’t make up for improper installation.

  • John R

    I will be contouring the shower floor to provide the proper drainage. Can anyone tell me what the slope should be? Also would it be better to build up the slope in multiple thinset applications, allowing it to dry between applications? That process would no doubt allow greater control on the consistency of the slope.

    Many thanks for any help.

    • Roger

      Hi John,

      The slope needs to be 1/4″ per foot. And it needs to be formed all at once with DECK MUD, NOT thinset. Use the search box above and read through the series about how to form a shower pan.

      • Monique Leslie

        Why not use thickset mortar?

        • Roger

          Hi Monique,

          It’s not a question of the strength of the bed, water needs to be able to flow through it. And most ‘thickset’ mortars (lft’s or medium bed) are only good up to about 1/2″ or so if needed. Mortar is for bonding tile to a substrate – nothing more.

          • Monique Leslie


            The reason I ask is that I have a shower pan that was partially built without a pre-slope (dam and membrane is in place). I’ve taken over the project at the point where there top layer is concrete (I think – it looks a little shiny, but ), and the guy who built told me it was mostly sloped, but that I might need to make the Versabond a little thicker in spots. I drew out the slope lines, and some places need as much as two inches to maintain a slope to the drain. One tiler recommended that I build it up with Versabond. I knew thinset wouldn’t cut it, so I bought LFT. What technique and materials do you recommend?

            Much appreciated!

            • Roger

              You need to make your shower floor decks with deck mud.

  • John R

    My current shower floor consists of a fiberglass base over which thinnest and river stones are installed. Since the stones are not touching, a fair amount of grout was used. I intend to apply thinset over the stones/grout surface and install 2″ X 2″ porcelain tiles. I would like to grind down the stones first but not sure what to use to grind them. Am I making a mistake? Any suggestions?

    John R

    • Roger

      Hi John,

      As long as they are bonded correctly it probably won’t be a problem. HOWEVER, you will be bonding tile to grout as well as bonded stone, that may cause issues down the road. I simply don’t know. It would be best to remove the stones.


    I have already tiled a tub surround using Mapei Type 1 thinset mortar. I also used this to set the corner shelf and soap dish by cutting the tiles and setting to the CBU substrate. We are selling the house on completion of the rest of the bathroom renovation so it’s not a huge deal for us long term but I also hate it if I just created a problem for the next owner. Did I screw this up?

    • Roger

      If your tiles are larger than 8×8 then yes, it could very well cause problems down the line. That is not mortar, that is mastic.

  • Marjorie Hendryx

    My tile guy wants to use deck screws instead of the screws recommended for the Jet-backer Board he is using. He is also not planning to use alkali resistant tape, but regular dry-wall tape instead with a layer of Redguard over it in the joints between the backer board. He is just going to cover the gaps between the backerboard and not the whole backer board with Redguard. He filled the joints between the backerboard with epoxy, but some areas look more like silicone. He had a siliconized tube on site. I can’t find any precedence for the way he is prepping the area for tile. Am I being too critical? This is a shower and I am concerned about leaks and mold.

    • Roger

      Hi Marjorie,

      It sounds to me as if he’s simply half-assing it. Why would he fill the joints in the backer with epoxy? That makes no sense at all. You are not being too critical, tell him to show you the specifications for the system or method he’s using. Every manufacturer has them, and they can be found in the TCNA handbook.

  • las65

    do i use thin set first then grout to lay tile,its a small closet

    • Roger

      Hi Las,

      You need to use thinset to bond the tile to the substrate (floor), then after that cures you fill in the grout line with grout. The grout doesn’t have anything to do with installing the tile (holding it), it simply fills in the grout lines.

  • Sergio

    Can i use mastic 500 for shower glass tiles. 12×24.
    5 1/6 thick.

    • Roger

      Hi Sergio,

      No. Call the manufacturer and they can give you setting materials you can use.

  • Ray M

    I just bought all new tiles for my bathroom remodel. The brand is Brennaro Splendida tiles that were not cheap. When I picked up my order the sales lady told me the the wall tiles in the shower area must be applied using tile glue, not thinset mortar, according to the manufacturer. I’ve never heard of this and couldn’t find any info on this requirement anywhere else. I’ve always used thinset in the shower area and refuse to use anything else, but I don’t want to ruin all these expensive tiles. Any insight on this dilemma will be greatly appreciated.

    • Roger

      Hi Ray,

      I have NEVER heard of anything like that. Did the supplier also sell mastic? :D I would contact the manufacturer directly – that sounds like a line of BS to me.

      • Ray M

        Yes that’s what I figured. She did try to sell me a tub of tile glue that I should use for an extra 40 bucks. I’m glad I didn’t take it though, thank you!

  • GeorgeM

    After laying the final top deckmud layer do I need to apply anything before I apply the thinset for the tiles?The reason I’m asking is the shower mud floor is really sand , does the thinset adhear to the sand.

    • Roger

      Hi George,

      It’s supposed to be sandy, it’s normal. The thinset locks in all that loose sand and it will bond extremely well.

  • Nina

    Want to lay porcelain tile on sub floor without using back board. Cost of labor and back board is really high. Is there an adhesive that can be used? Floor has carpet and vinyl now, is over a basement. Doing close to 900 sq ft

    • Roger

      Hi Nina,

      You said basement, is your subfloor cement? If so, yes, you can remove the carpet and vinyl and bond it directly to the concrete. If your subfloor is wood, no, you need an underlayment.

      • APSanders You need to use a an uncoupling membrane over concrete. Because concrete will expand and contract with temp change also for concrete cracking. This will keep you tile from cracking or grout from cracking.

        • Roger

          It is not NECESSARY, simply recommended. And a good idea. But it can absolutely be bonded directly to concrete.

  • Guy G

    I am tiling my shower floor and bench with 18 X 18 tiles. What mortar do I use? And how should I do the front corner on my bench? top tile on top of the front tile?
    Any help would be greatly appreciated.

    • Roger

      Hi Guy,

      There are a lot of proper choices for thinset for your tile. Mapei ultraflex, versabond, laticrete 253, etc. It mostly comes down to what is available near you. Yes, top tile over the face tile. I normally put a row of bullnose tile across the front of the bench so you have a finished transition there.

  • George

    You are way too busy Floor Elf! Have a beer!!!! ?

  • Jim Willoughby

    Question I putting a floor in my daughters shower actually a complete rebuild. I am down to the floor and someone sold her Redi poxy to glue the small tile in the shower. I have read comments about the Redi poxy setting very quickly. Since i work by my self and i am an old man and work slow. I am worried about the poxy setting up on me. I have no instructions on mixing small amounts. My question is what is best for this job?

  • Jesse

    Ok here’s my delima. I installed a nice porcelain tile shower tiles are 12×24.
    I was going to use corner metal shelves, (soap/shampoo) that matched shower. Shower complete. Nice job if I say so my self. Since then the wife wanted granite counter top and on tub deck lid. Now here the delima she wants to use the same granite for the corner (soap/shampoo). Question is do I have to tear out tile and install granite. Or can I epoxy it to tile (cutting slots in it and wall for biscuit) and glue it to wall?