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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Hi Roger,
I have a polyurethane shower base that is securely sealed in a mortar bed, but is 1/8″ off on the level from the drain. Can I level off with epoxy, let it harden then lay down tile on top of that with epoxy?
Hey Scott,
Not really a good idea – the pan is not made for that and the bond long-term is untested. It may work, it may not, I honestly have no idea. Never had any reason to do that. I do not, and really can not, guarantee a failure – I can only give advice about methods that are guaranteed to succeed. That said, people do stuff all the time that is not an ‘approved’ method and it works just fine. However, they also do many, many more which don’t work out so well.
I’m a lot of help, huh?
Roger,
I had a tile floor installed on a cement subfloor. The installer used a thin set mortar and I had the floor leveled off years before for a floating hardwood floor. The contractor and flooring guy said that if there was any other areas that needed leveling that the floor was fine and he could use the mortar.
Little Elf continued….
So after all was done with some areas of tile being not level and between 1/8 and 1/4 of an inch difference between adjacent tiles, these tiles that are higher seem to have no mortar underneath? For example if u bounce a golf ball on a tile that seems to have not been set in the mortar it has a hollow or echo sound. So would those tiles be more prone to cracking and damage over the long term and was this a bad installation?
Hey Little Elf (if that is your real name
),
That is a very, very significant height difference. The ones that sound hollow probably simply have less thinset beneath them. They aren’t necessarily more prone to cracking (unless he had incomplete thinset coverage) but that is something you really can’t predict without taking one or two up and seeing how the coverage is beneath it. Yes, it was a bad installation, the maximum allowable lippage depends on the individual tile but is rarely over 1/16″ height difference, even that is a lot, and NEVER more than 1/8″. Attempting to level part of the floor that much lower normally requires a medium-bed mortar which doesn’t shrink as much.
HI. I am installing a tile redi shower pan. Need to replace a loose ceramic tile. I do not have more epoxy. What can I use in replacement of buying a bunch epoxy? Can you use thinset on polyurethane shower pans? Thanks.
Hey Jeff,
Nope, thinset won’t bond to the polyurethane. You can get any regular epoxy at a big box store. If you’re only fixing one tile any epoxy product will bond just fine.
I have a pebbled concrete floor that i would like to put porcelin tile on. Can i use thin set over this floor to install the tile.
I would appreciate your advice.
Thanks
Hi Robert,
Unfortunately no. If it’s the pebbled tile floor I’m thinking of it’s just little 1/8″ or smaller pebbles locked into a surface in a bed of epoxy. This type of flooring will peel or chip up in layers. It is not stable enough nor adhered enough (in most cases) to have a tile installation over the top of it.
The floor i have is pebbles on top of a concrete slab in my screened area.
Robert
That should be able to be removed in layers. A lot of times you can simply scrape it up off the concrete. Tile installed on top of that is relying on the bond of the pebbles to the concrete in order to last – that is rarely a competent bond for long-term durability of a tile installation.
Can Hardi Board be applied over the pebbled surface using thin set as a base for tile
Robert
Hey Robert,
Nope, won’t last long-term. That type of floor covering (pebbles in epoxy) IS NOT suitable in any form to have tile installed above it. If you want tile over that concrete slab, and want it to last, it MUST be removed.
Thanks Roger for the info. I appreciate your taking time to answer my questions.
Robert
Un-modified VS Modified
My project is a tiled shower. I have selected Hardie Backer 500 and Schluter Kerdi for substrate and water proofing. Hardie Backer instructions calls for modified thin set and Schluter Kerdi calls for un-modified thin set. Is there any risk of using un-modified thin set to bond the Kerdi to the Hardie? I would like to say you have a great site, I have read a lot of your posts and articles. Thanks to your site I have found information most valued in planning my project and yes the no holds humour has made reading enjoyable.
Thanks again,
David
Hi David,
Absolutely no risk at all using the unmodified over hardi provided you use a quality unmodified like Laticrete 317 and not that $5 / bag customblend from home depot – I wouldn’t weigh down the back of a pickup in the snow with that crap.
Rodger
I do not have access to Laticrete products in my region. I picked up PremiumPlus standard thin set, @ 20 buck a bag I’m hoping this is simlier to Laticrete 317.
Thanks,
David
Yup, that’ll work just fine.
Rodger
Thanks a bunch for the help
David
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