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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  • Truckee Jim

    I’m setting mesh backed mosaic glass tile on gypsum board for a backsplash and I’m seeing a lot of conflicting advice. To prime or not to prime and with what? I found a thinset from laticrete specifically for glass but it excludes mesh backed tiles. Which thinset is best for this application? (I really don’t want to use epoxy, it sound like as much fun as going to the oral surgeon)

    • Roger

      Hi Jim,

      Laticrete’s glass tile thinset will work fine with the mesh-backed glass. There is conflicting advice because every professional has their own way of doing it that makes it comfortable for their projects. My general rule is to only prime if the paint on the wall is the glossy variety (which it rarely is). If you do want to prime, regardless of the type of paint, you can use Killz. I rarely prime for backsplashes.

  • Paul McManus

    My daughter just had her backsplash installed and the work was done with mastic. The installer did a very nice job but the marble is turning a light yellow in spots.( not good)
    She has read that you should not use mastic with this marble. Each day more tiles turning a yellowish color. Was installed less than a week ago.
    She has asked installer and and person installing kitchen to take out and do properly. They are going back and forth.
    Your opinion please.
    Thank you Roger.
    Paul McManus

    • Roger

      Hi Paul,

      While mastics are fine for a backsplash application, they are NOT fine for most natural stone applications, regardless of where it is installed. Mastic is an organic product, which means it has an oil base. In porous natural stones such as marble, these oils will leach out of the mastic and be absorbed by the stone, which is why you are seeing yellowing.
      The installer is wrong. You can look right on the bucket of mastic he used – it will say not for use with natural stone. Just tell him to show you the bucket and point that out to him.

  • Elvin

    I’m using 4ft by8ft sheets of metal weilded solid with a 2 inch fall in 8 ft to make a floor on my outside balcony I would like to tile this it will be walked on I also plan to have a room under this that is water proof can I use thin set mortar to install tile on the metal dimensions are 8 ft by 24ft long

    • Roger

      Hi Elvin,

      No you can not. It will not bond long-term. The expansion and contraction of metal, which is a LOT (by tile standards) will cause the mortar to unbond. You may be able to use an elastomeric membrane like hydroban or redgard over it, but you need to contact the respective company and find out if their product will work over the metal.

  • Bob D.

    I know its wrong but i am making a bathtub with bianco polished 12×12 marble tile first layer concrete board then self leveling bed covered by 1/4 aluminum watertight floor and walls of tub 1 layer of brushed on membrane but cant decide on what morter to use and or grout please help

    • Roger

      Hi Bob,

      I would love to help, but honestly it’s going to fail anyway so it wouldn’t do you any good. Sorry.
      Aluminum expands and contracts A LOT when exposed to temperature differences. When you pour hot water into that ‘tub’, the aluminum is going to expand.
      Tile requires a relatively stable substrate – aluminum IS NOT it. It will not work the way it needs to.

      The first clue that you should not have done this is your first sentence: “I know it is wrong but…”. You should have stopped at the first four words.

  • Judith Willimson

    Thanks for you site.
    I’m planning to use the Kerdi membrane on our curb-less walk in shower. The entry is planned to be a tiled arch, extending out for a tile width onto the interior and exterior walls of the shower. Our drywall contractor has a flexible plastic form he plans to use to form the arch. He has suggested using mastic on the curve, which I know now, is definitely a mistake. How would you handle this situation?

    • Roger

      Hi Judith,

      You can use thinset for it, or you can use regular drywall mud then, after it cures, cover it with kerdi to waterproof it.

  • HereInOhio

    I am installing carrara marble tile around my fireplace (on the floor and the wall). The wall tile is a drystack style with small pieces (1/2″ tall x 1 to 2″ long) with an very rough or raw front. I’m wondering what thinset you would recommend (make and number preferably). I know to go with white and assuming to go with modified since I’m not going over a kerdi product like on the floors but I’m unsure of the best product as far as adhesion time and strength.


    • Roger

      Hi Hereinohio (if that is your real name…),

      Mapei ultraflex 2 or laticrete 253 gold would be ideal for your installation.

  • Marie b

    Hi. I’m new at this and I like doing diys well because I dont have much money to spend on pros. I want to do my bathroom wall not shower or floor, just the wall in front of the toilet and above my vaniety in River rock. I plan on making the tiles myself.Now I’m remodeling the whole room. It’s a mobile home and it has that real thin drywall. Do I need to take the drywall down and replace with plywood? Or what is the best to rock?
    I’ve been doing my home work on educating myself on thisset mortar, grout, sealent. I just need a little more help. If you could give me some advice it would help and by that I meant step by step. Please

    • Roger

      Hi Marie,

      The thin drywall will work, but it would be best to replace the thin drywall with regular 1/2″ drywall. Then just mix up thinset and bond the rock to the wall. Fairly simple process.

  • Dean E Tribbett

    What type of thinset is best for laying porcelain tile over ceramic tile floors. My existing tile is not cracked and is well adheared to a slab. I plan to scuff the tile with a diamond cup grinder and apply Eco prim grip before laying the tile. Tile Shop tried to tell me to use epoxy but I really don’t want to deal with that as I have never used it and I am very slow and detailed so I would feel rushed with set/bucket time. I am thinking of using Flex bond instead. I need the extra height and taking up the old tile from a slab will be a PITA.

    • Roger

      Hi Dean,

      Flexbond would work fine. Epoxy is not needed. The tile shop is in the business to sell stuff, and they try to sell EVERYTHING. :D

  • Cynthia


    I am installing an onyx mosaic tile and saw some photos of a backsplash you completed a while back. Can you tell me what bonding agent should be used as well as the type of grout? I am concerned that I will ruin and discolor my onyx.


    • Roger

      Hi Cynthia,

      Regular white thinset will work just fine. I use regular unsanded grout (due to possibility of scratching the onyx). You may get ‘framing’, which is simply moisture from the grout soaking into the sides of the tile, but it will dissipate and disappear over time.

  • joseph

    Going to install split face natural stone (mosaic) tile 6″ x24″x 1″ around gas fireplace on flat 8′ wall and researching for answers to a few questions. The stone may be slate but its slightly dark gray.
    What would be best or better products for attaching these? I’ve heard the use of specialty products for stone or large area tiles. not sure.
    Will be installing 1/2″ hardi backer and taping seams. Do i also need to use wire mesh? I’ve seen some people use it.
    should I begin the installation at top of fireplace on ledger and then do below once it sets? Or does it matter?
    Should I limit my progress to a few vertical feet per day?
    Since stone will be installed on a wall with no return exposing ends of stone, how do I make the edge presentable without showing setting material and not using a surround? Thanks in advance.

    • joseph

      also, its called ledger panel. does this affect the installation?
      the pic depicts the actual stone in similar installation.the edges will be visible and on flat wall. only difference is, i will not use a mantle.

      • Roger

        Hi Joseph,

        Regular thinset works fine. No need to start with a ledger. No, do not use wire mesh. You should be able to do as much as you want per day. You can miter the edge of those for a return on the ends.

        And yes, I realize this reply is likely too late, but the info will be here for others in the future. Sorry for the delay.

  • Gary K.

    Help Please,

    I have a very large quantity of still well within date plane old West System epoxy glue…and a lot of experience using it in my cabinet making shop.

    I would like to apply porcelain tile (12 by 27 Inches) over a very stable and non flexing formica topped counter to modernize/ improve the look of our kitchen.

    Other than the usual concerns about working with epoxy would you have any reservations. I will of course first verify that it will stick to the formica/ arborite or whatever that stuff is. Quite certain thinset etc will not adhere…initially considered belt sanding with P40 or something but then just thought of my jugs of epoxy. (Could of course apply plywood on top of the counters but the edges would be getting quite thick.

    Or in other words how does epoxy based tile adhesive differ from my plane old 2 (or 3 with thickened) epoxy glue?

    Many thanks for your comments,


    • Roger

      Hi Gary,

      It doesn’t differ much, but I don’t think it will bond to formica long-term. Formica is stuck to plywood with contact cement, heat it up and scrape it away.

      And yes, I realize this reply is likely too late, but the info will be here for others in the future. Sorry for the delay.

  • Helen

    Hi Roger,
    we’re going to install 8″x16″ ceramic tile on our bathroom walls (all around, top to bottom). According to the rest of the internets, it’s considered “large format tile” because it exceeds 15″ on at least one edge. But according to your guidelines it falls into the regular category.

    Would you use LFT thinset for this size? It’s kind of borderline… I’m looking at Mapei Lightweight or Kerabond.

    Thank you!

  • John

    Hey Roger, in your manual for kerdi, you say to use thinset to do the final set of the kerdi drain, should i be using the tile morter or deck mud mixed wetter.

    • Roger

      Hi John,

      The tile mortar.

  • John

    Hey roger, ive picked up some kerabond (grey) for using with kerdi membrane, do you think it will be a problem with 12×12 white tile and grout. They dont seem to have an unmodified white.

    • Roger

      Hi John,

      No problem at all provided your tile is ceramic or porcelain and not natural stone.

  • Marie

    Whenever I follow the instructions (i.e. Amount of water) for mixing thinset mortar, I find the mortar is way too thick. By that I mean extremely difficult to spread. It also does not smooch down when the tile is set on it, and thus does not give good tile coverage. Can you suggest another way to determine how much water to add? Thanks.

    • Roger

      Hi Marie,

      I do it by feel and look now, so it’s difficult to explain with words. Add a little more water is about all I can tell you. You don’t want to add a lot more, the mixture is tested in lab conditions and is optimum for the chemicals in the thinset. You want it about the consistency of creamy peanut butter.

  • corey


    When using a liquid topical for the walls what do you do about the valve openings? I have quite a few (showerhead, body spays, hand held, valves, and diverteres). Would I be better going with kerdi so I can use the gaskets?


  • Rod

    Thank you for your website and excellent instructions. About a year ago, I used them to build and tile a new walk-in shower and heated bathroom floor. My wife is so impressed that she’s informed me I’m now qualified to install a tile backsplash in our kitchen (happy wife, happy life).

    The backsplash tile consists of random pieces of glass and ceramic that vary from 1/4″ to 3/4″ wide and that are 3″ long. They are arranged onto 12″ x 12″ mesh mats. The kitchen is about 12 years old, and the backsplash area is currently painted drywall.

    Based on your information regarding setting materials, I understand that although mastic could work in this application, thin set mortar is preferred. However, what, if anything, should I do to prepare the painted drywall before attaching the tile? It would be a pretty big job to cut out the drywall and replace it with cement board.

    Thanks in advance,

    • Roger

      Hi Rod,

      You can go right over the drywall as it is. And with ANY glass tile you have to use thinset, you can not use mastic – it’ll never cure under the glass.