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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Jon Sall

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

Reply

Roger

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.

Reply

Jack

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?

Reply

Roger

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.

Reply

Greg

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

Reply

Roger

Hi Greg,

Welcome to my world. :D 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.

Reply

michaelene

Hi Mark,

We are tiling bathtub shower surround with tile size 12 x 24″. What type of mortar should be used?

Reply

Roger

Hi Michaelene,

It depends on what your tile substrate and waterproofing method is. Most of the time a good modified mortar works just fine.

Reply

Mark

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

Reply

Roger

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.

Reply

Mark

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

Reply

Roger

Hey Mark,

Yes, provided your substrate is sturdy you can go right over those with thinset as you are installing your tile.

Reply

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