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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Dewey

this summer I want to install some tile, rated for exterior, on a porch slab. This is in Iowa with minus 20 degree temperature in winter. do I need to use epoxy or is thin set OK?

Reply

Roger

Hi Dewey,

Thinset is just fine.

Reply

Stuart

Hey, Roger! I’m over here now!

After reading your latest posts on modified and unmodified thinset and this page about proper setting materails, I still don’t know when to use which type of thinset. Specifically over a liquid waterproofer like Redgard. Can you point me to the deets please?

Reply

Roger

Hi Stuart over here!

About the only time to use unmodified is with schluter products. All liquid membranes require modified thinset, including redgard.

Reply

Stuart

Thanks again. I’ll go with your recommendations on modified thinset.

Reply

Stuart

Dammit! I thought I could figure this one out myself…I was thinking you had an article where you listed all of the common modified thinsets and rated them. Well I can’t find it. I did find the post about unmodified thinset in which you did just that but cant find the info for modified stuff. I’m going out today to get thinset to tape my seams and corners and to use to set my tile over redgard but I’ve read so damn many posts, replies, guides, etc here in the 24 hours that I’m losing my mind.

Thank god you are a patient man.

Reply

Jon

Hi

I have to replace a couple of broken pool tile can I use thin set to make the repair

Reply

Roger

Hi Jon,

Yes.

Reply

bill

Hi
I just finished a shower floor with premixed simple set mortor and just saw It should not be used on shower floors.do I need to tear it all up?Ive allways mixed mortor in the past and thought I would save some time would this last after grouting or not?

Reply

Roger

Hi Bill,

Yes, it needs to be removed. No, it will not last.

Yes, I know that isn’t what you wanted to read – sorry.

Reply

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