Proper Setting Materials for Tile

by Roger

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.

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Tim

Hi Roger is there any way to take motar set 2 and speed it up

Reply

Roger

Hi Tim,

I have no idea what mortar set 2 is. You can speed up regular thinset by adding baking soda to it.

Reply

Jon

Quick complete novice question: I’m planning to mix a little thinset at a time so I can work on small areas and avoid skimming. Is it OK to mix up the new batch in the same bucket as the prior batch – i.e. while there is still a little left at the bottom from the prior batch that hasn’t dried out too much? Or do I need to start with a clean bucket for each batch? Thanks – really appreciate all the effort you put into helping the DIYers on this site.

Reply

Roger

Hi Jon,

Clean bucket for each batch. I know it’s a pain in the ass, but existing thinset will cause the new stuff to fire off more quickly and you won’t have nearly the same amount of working time with it.

Reply

Robt

I am replacing an 18″ high row of 4 inch tiles in my shower (exterior wall). This resulted in an 18″ vertical seam in the hardie backerboard. Do I have to tape this small seam? It bugs me that I’d have to buy an $8 roll of tape for this little seam.

Reply

Roger

Hi Robt,

I’m sorry it bugs you, but yes, you need to tape and mud it. Would it bug you less or more if it fails and you need to replace the tile again? :D

Reply

Applebaum

Hi Roger,
I am a novice when it comes to doing shower tile installation but a pretty handy person. Ive been following your site and I also purchased the eBook. My issue is that I am ready to tape my hardibacker and everything Ive read on this site and others say to use the thinset to embed tape. Everything I read says to use the same thinset to adhere tile. My tile are 9.75×16.25 which are considered large, so do I use thinset to tape and adhere or do I use medium bed to tape and adhere. Or do I use thinset to tape and medium bed mortar to adhere even though its my understanding I should not be mixing. Please advise.

Reply

Roger

Hi Applebaum,

You can use either.

Reply

binh

I’m prepping my concrete slab for tile look wood for almost the entire house. I have roughly over 1,300 sq feet of concrete slab. The old slab has several long horizontal cracks no bigger than 1/16″ and one nearly 1/8″. I am firm believer of doing it right the first time; therefore, I chased most of the cracks wider in order to bridge them.

I am using Sika 32, which is a 2-component epoxy mixes for the cracks. I will be grinding them flush once the epoxy dried. Have you ever taken this route when tackling cracks in concrete slabs? Or should I have gone with crack suppression membrane in the first place? Also, now that I have filled most of the cracks with epoxy, do you think/know the thinset will adhere to epoxy if I roughen it up once dried? Epoxy dried hard, but kind of shiny and slick.

Thanks,
Binh

Reply

Roger

Hi Binh,

No, I never have. I prefer the crack suppression membrane. If you are installing directly to that slab then I would still use a membrane over that epoxy. I am of the opinion that, no matter how strong your epoxy, you won’t be able to epoxy the slab back together. That is essentially what you’re doing since it has already proven to be the weak points in the slab. Higher end thinsets will bond to roughed up epoxy, like laticrete 254 and mapei ultraflex 3, but I honestly wouldn’t trust that bond long-term. Epoxy has zero pores for the portland crystals to grow into.

Reply

Karen b

Thanks Roger,
What would he have to do to fix the cracking? This is my first house and shower that we have done and I’m trying to make sure that we don’t have a bigger problem later on. Also, I have him installing a laurel mountain whirlpool tub; and in the instructions on how to install it saw says that it must be supported by the ground floor and not the rims but my husband and I opened the panel where he still has to tile. But that’s not how he did it, he just put a blob of mortar in the middle of the tub which is barely touching. Another thing that he did was, he built the frame before we had received the tub which I had asked him to wait just in case because even though He had specs of the tub its sometimes wrong but he still built it without having the tub, will he have to re-build it or can he just get pieces of plywoods and put it on the bottom for support? Thanks :-| :-| :-|

Reply

Roger

Cracking is normally indicative of movement in the substrate. It could be a number of things, improper substrate, improper coverage, improper grout mixing, incorrect type of grout (unsanded for grout lines larger than 1/8″). The fix would depend on the cause.

He can use plywood to support it, but the mortar under the tub is also an acceptable method (one which is skipped normally, it needs to be there ALWAYS). Even when the tub contacts the floor you should have mortar beneath it to fully support the base of the tub.

Reply

Matty

After reading a number of pages and posts, still not sure when it is worth it or a must to be using an uncoupling membrane, I get that it’s to keep tile safer from cracking, provides something to allow small movements in thinner modern building methods that used to be done by thicker layers of various materials in olden times, but I’m still confused by the need or lack of need for an uncoupling membrane such as ditra. When is it good idea, unnecessary, or a better or worse installation method than installing ____ directly on ________ substrate…. For example, a concrete basement floor slab, … over joists plywood, mortar and cement board, walls…. Size of tiles, Could you add a post that gets into this for the novice?

Reply

Roger

Hi Matty,

It is ALWAYS better to have an uncoupling membrane. Concrete moves and cracks – a lot, a membrane will compensate for that. Wood moves – a lot, a membrane will compensate for that. In my opinion you are always better off. Uncoupling membranes do not go on walls. If you have cement board on your floor, while a membrane is not necessary, it is still a helpful.

Reply

Al Gegaregian

Hello Roger,

I am in the process of repairing loose shower wall tiles that are located above an exposed pan floor. I have removed 4 courses of 3″x3″ tile above the pan that are on a 1/2″ thick mud base. The mud base was applied to 1/2″ green board. I have also chipped off the mud base below the removed 4 courses of tile. The green board is not soggy, in some areas the paper was damp but the board appears to be sound.
Now for my question. I want to replace the removed 1/2″ mud with 1/2″ Durock instead of mud. My concern is at the horizontal seam between the mud and new Durock. Should I use thin set to butter up the joint edge between the existing mud and new Durock, what would you suggest for this seam. I have tried to remove just the tiles and leave the mud in place for at least 1/2 tile width so that I could use a mesh and thin set lap joint, but have had limited success in keeping the mud base on the wall it chunks off with the tile. My last ditch approach is to try to route out the mud at least 1/2 in from the edge of the tile and butter the Durock up and feed it into the 1/2″ cavity.
I don’t know what else to do at this point, your suggestions are appreciated.
Thank you, Al

Reply

Roger

Hi Al,

You can simply tape and thinset that transition, that will work just fine. The bigger issue is the greenboard. It works just fine behind mud, but it won’t behind cement board. You need to remove it where the cement board is going, shim out the studs, install a vapor barrier over that, then install the cement board.

Reply

Karen b

Hi roger, I wanted to ask you is 2600$ for doing a tiled shower a good price?
It does not include tile cost, or valve and faucets. Also, I am questioning his price because I keep seeing my grout cracking and I don’t think he sealed the grout or the porcelain tile. I asked him for corner shelves and all he did is put 2 tiles together and cut them about a quarter of a tile in a triangular shape and put it there, charged me $85 for both is this what is normally done? Not what I wanted or expected. I’m quite upset help.

Reply

Roger

Hi Karen,

Price is relative and not something I attempt to discuss on this site. That is a great price in NY, and extremely expensive in WY.

If the grout is cracking something is incorrect and needs to be fixed. I have done corner shelves like that, but always use a bullnose on top and have a finished edge – I never do them like that. And no, that isn’t how they’re normally done.

Reply

randy bullen

working with A GC. His tile guy has never heard of slaking. although he lays tile with perfect grout lines, the lipage it is so bad it’s referred to as toe stoppers. The lack of floor prep is driving me insane. lays directly on paint and drywall over spray on the floor. my question is is it allowable, proper,smart to mix regular thinset with fast setting thinset? I have worked with many tile people over the years and none have ever mixed the
two. seems like a terrible idea to me.

Reply

Roger

Hi Randy,

You never mix thinsets. Ever.

Reply

Kathleen

So, you can really use thinset to install waterline tiles in a pool? How about using it for a mosaic design on the wall of a pool where it will be completely submerged?
And, grout? What type should be used in both applications?

Thanks in advance for your time.

Reply

Roger

Hi Kathleen,

Yes, you can. Any cement-based product actually becomes stronger if it’s submerged. I would use epoxy grout, but I’m not a pool guy and there may be ramifications from the chemicals in pool water. I would contact the manufacturers of any products you intend to use to ensure it will work in a pool application.

Reply

Shane

Hi Roger, I’m working on a shower following your site and it is going very well. Thanks for all the help. Question for in the rest of the bathroom where we want to tile half way up. It is a basement bath and will get wet from shaking dogs, but hopefully never really soaked. The only drain will be in the shower (on the other side of the curb). On the bathroom walls, should I install the tile on 1/2 backer board or just install it on moisture resistant drywall? I apologize if I an answer to this on your site.
Thanks again,
Shane.

Reply

Roger

Hi Shane,

The drywall will be just fine in that application.

Reply

Julie

I have six 8″ square decorative tiles which complete a picture when placed in a 2×3 arrangement. In order to display them as a picture, I have had a custom frame made of aluminum (it looks like a cookie sheet). How / what do you recommend I use to adhere the tiles to the frame?

Reply

Roger

Hi Julie,

You can set them with epoxy.

Reply

Suzanne Bayder

I am working with a tile contractor. My tiles are 24″ marbilized porcelin for 1500 sq feet. He wants to use a thin set vs mud set. I am told only a mud set should be used with 24″ tiles. Which is correct. Are there cicumstances when you can use a thin set vs mud set on this job ? He is charging $6,000.00 to install a thin set. Is this a fair price to complete the job

Reply

Roger

Hi Suzanne,

A thinset is fine. What you are referring to as a ‘mud set’, I believe you mean a medium-bed mortar, which is also fine. A lot of factors come into play to determine what is appropriate. Fair price is relative. :D I will say that’s a hell of a lot cheaper than I would do it.

Reply

regina

Hey Roger

Maybe you can advise me, I am laying Faux wood floor tiles over my existing tiles, I had two quotations today, second guy said I absolutely have to use formaflex, that’s what its called here in Spain, to glue the tiles down, problem is its 15€ per sq meter, works out the same price as the tile…!! can I not just run with the mortaro?

Please help

Regina

Reply

Roger

Hi Regina,

If you can scarify the existing tile so that it will soak in water when you splash some on there then regular mortar will bond just fine to it. But they need to be able to soak water in or it won’t bond correctly. If you use the formaflex you don’t need to do that.

Reply

Angel

Thanks Roger, I will be using ditra as a substrate so unmodified it is…

Reply

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