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.
{ 19 comments… read them below or add one }
Hello Roger,
I am learning quite a bit from your site and really appreciate that you take the time to educate all of us who like to do it ourselves. I wrote previously about our upcoming master bath project using onyx. Will the thinset work with the onyx or do we have to use epoxy adhesive? I take it from all the reading I’ve done, we should use the spectralock epoxy grout. Is that the right choice? I’m sure I’ll have more questions over the next couple weeks and I thank you for your time and expertise!
Hi Elizabeth, welcome back! Glad I haven’t scared you off!
Unless your onyx is from a very unique manufacturer, and you would know if it was, you should be fine using a higher-end (read expensive) modified WHITE thinset. Be absolutely certain you use the white. The color of the thinset will show through due to the translucence of the onyx. If you use gray it will show through and significantly dull the color of your onyx.
Just to be certain, though, you should be able to contact the manufacturer to see if epoxy is required. If it is they will let you know. Every manufacturer will tell you anything you need to know about their product – they want it to be installed correctly and want it to last. They will tell you how to make that happen.
Spectralock is absolutely the way to go. As I’ve previously stated it is the ONLY epoxy grout I will use – period.
Thank you for the kind words and the time I spend is absolutely my pleasure if it helps people avoid incorrect installation and, in turn, developing a negative opinion of tile in general and contractors such as myself in particular. I’m only out to save the world. I’m just super cool like that.
I’ll always be here for any further questions you may have.
We just tiled our kitchen counter tops. We used a non-sanded grout (1/16 grout lines). We used a silicon sealer on the grout lines according to the manufacturer’s instructions. Recently, I’ve noticed that the grout is shrinking and pulling away from the tile… what gives?
Hey Nick,
The problem has nothing to do with your sealer – it’s a grout issue. To be able to help I would need to know the type of grout (brand) you used as well as the color. If it is a darker color it tends to set up more quickly which means it probably never got a good grab on the tile in the first place.
If it started to set up prematurely it never would have grabbed the tile and probably had micro-cracks along the edge of the tile which you would not have been able to see. The grout continues to shrink as it sets and is not fully cured for about 28 days.
Unfortunately there really isn’t much you can do except this (and yes, I know you don’t wanna hear it – sorry) The best thing to do at this point would probably be to dig it out and regrout it. Make sure you follow the directions on the grout to the letter as far as the amount of water and working time.
You may also want to consider using a sanded grout. I use sanded in just about everything I set including 1/16″ grout lines. The sand prevents the grout from shrinking and holds the size while it fully cures. It’s a bit more difficult to ensure you get the grout lines full but a small price to pay for the piece of mind in my opinion.
Hope that helps. If you have any more questions please feel free to ask.
Hi Roger,
Thank you for all of your advice. Similar to Barabara’s comment (July 12, 2009) I too have a shower floor that needs to be regrouted (mainly around its perimeter, but I’m willing to regrout the entire floor if necessary). The whole floor is not horrible, but mainly the outer edges of the floor are full of mold and it appears that the former owner recaulked over the grout and old caulk without removing any of the old. Also, from what I can see, substandard caulk was used (I’m guessing as a quick fix to sell). My thoughts are, removing the old grout on the floor with grout saw as well as all of the old caulk/grout in the corners and planes (where floor/walls meet). Per your previous comments, I will plan on buying standard unsanded grout (since the lines are 1/8 inch) to regrout the floor. However, should I use grout for the plane areas or should I use caulk? If I should use caulk, could you please recommend the proper caulk to use at the planes as all the recommendations I’m getting from HD or Lowes are to use Keracaulk which is Siliconized Acrylic Caulk (Mastic) which from what I’ve read on the back of the product “is not for use in areas prone to constant water exposure” — ??. When I showed this to the Lowes employee he simply stated “look at the picture, its a shower floor”. HELP!!!!! What’s a girl to do? I’d appreciate your thoughts/insight!
Hi Suzanna,
‘Look at the picture!’
That cracks me up and, unfortunately, is typical of the response of their ‘experts’. Sorry, that just gave me a laugh.
TCNA standards state to use caulk at all changes of plane. That’s just fancy pants talk for ‘corners’. Although I don’t always do that (I’m a rebel like that) you should. I will oftentimes use grout simply because I built the shower from scratch and I know how much movement is likely.
In any wet area ideally you want to use 100% silicone. Be aware, however, any type of caulk you end up using will need to be replaced periodically, It’s meant to be waterproof, not permanent. About every year to 18 months is when I scrape mine out and recaulk.
Now I’m gonna confuse you.
If your grout lines are indeed 1/8″ I would actually use sanded grout for the floor. It would be a better and more durable solution. Not imperative, just a better choice. And without regrouting the entire floor it would be difficult to match the existing. Little more work but it would end up looking better.
You may want to have someone take a look at your shower to determine the cause of the discoloration. If it is, in fact, only discolored around the perimeter that is actually indicative of an improperly draining shower – maybe. Don’t panic
just something to keep in mind. If part of the grout (around the perimeter) still looks wet while the rest is dry that could be a problem with mold, improper drainage, etc.
can a natural slate withstand freeze/thaw on a front porch? red guard? special mortar or grout? whadayado?
Hey Bill,
Slate can withstand the freeze-thaw cycle fairly well as long as you have proper slope for drainage (1/4″ per foot) and there are no spots for standing water. If properly sloped any moisture soaking into the stone would be nominal and no problem.
You can use redgard or, better yet, ditra. Also use a highly modified thinset to adhere the ditra to the concrete and a good unmodified to attach the tile to it. Ditra creates a mechanical bond rather than a chemical bond so you don’t need to worry about the bond releasing due to weather.
thatswatido!
Hope that helps.
Hi Roger,
Here’s a non-ceramic flooring puzzle/issue for you that I’m hoping you might have an answer to. My husband and I are looking at a foreclosure house to buy that clearly at one time had a water issue in the basement b/c the sellers (the bank) just put in a french drain and new sump pump a few months ago. The basement floor is covered with linoleum(or whatever they are made of now) tiles. During our inspection, we started noticing that there was a dark brownish liquid spotting the floor and then realized it was coming up through the cracks between the tiles in places–particularly if we stepped on the edges. Our inspector was at a loss initially and thought it might be that the new drain wasn’t working correctly or that there was a broken sewer line. There was no sewer smell and the liquid had a slightly oily smell and was thicker than plain water. The house was built in 1946. New tiles were laid on top of old tiles. The newest flooring was laid much more recently, but we don’t know when. Later our inspector said that some older adhesives had a tar like quality and if they got wet they could emulsify. Our inspector thought but was not confident that might be the case and since the basement had been wet at some point (hence the drain installation) that these older adhesive take months to dry back out, especially when a newer layer of tile is placed over it. Is it possible that this liquid we are seeing is a liquified adhesive? Does this really happen?
Hi Tracey,
Yes, this does really happen.
Kudos to your inspector for figuring it out. It sounds to me as if that is exactly what is happening. The older adhesives that were around in 1946 were organic based adhesives which required air to dry. The product of choice at that time for basement floors in many areas of the country was a VCT (vinyl composition tile) type of tile. The mastic or glue used to install this was brown in color and did re-emulsify with prolonged contact to water (like a flooded basement).
When this happened it was usually fine to let it set and dry out, which it would do over the course of a week or two, with no lasting problems. The problem you have is that layers of newer flooring were installed on top of this which SIGNIFICANTLY cuts down the ability of air reaching the re-emulsified adhesive below your original tile. The fact that it is an evaporation based curing process for these adhesives effectively eliminates the ability of the floor to fully dry out. When you step on the floor you are forcing the re-emulsified adhesive up through the cracks because there was initially only enough room below the tiles for the adhesive, now it’s mixed with water and the volume can be twice as much as the original amount. There’s just too much stuff under your tile.
The good news, should you choose to look at it that way, is that it is easily removed.
Once this adhesive re-emulsifies it allows the tile to be essentially peeled off the floor in most cases. So yes, it does happen, and no, it doesn’t cause structural damage of any sort to the concrete below it. It should be replaced, though.
Hope that helps.
Thanks, Roger.
I’ll be using the thinset between the joints of Hardibacker, with Redgard over the Hardibacker, and setting the tile with thinset. Hope I’m not stating the obvious, but it sounds like a modified thinset will be ok since it will have time to dry before the Redgard goes on and will be able to dry beneath the tile.
Thanks for your help on this as well as the insulation questions. Your site has been a big help to to someone who didn’t even know what thinset was at the start of the project.
Hey Mike,
The regular modified thinset will work just fine for you.
Glad I could help! If you have any more questions at all please don’t hesitate to ask.
For unmodified dry thinset, the manufacturer recommends using “admix”, which I think is liquid latex, along with the water. Does using the admix negate the good properties of dry thinset mentioned above?
Hi Mike,
Yes, admix is liquid latex. It will not negate the properties of thinset. If it says it only meets ANSI specs if you add the admix I would take it back, that is an inferior thinset. Some companies make thinset that only meet specs if you insert admix, that isn’t what you want.
Also if you are using a membrane such as Kerdi that specifies an unmodified thinset you should not add the latex to it, that effectively negates the reason for using unmodified which is that the latex needs air to cure. When you place a waterproof membrane such as Kerdi over it, it will take forever to fully cure.
If you are using the unmodified for a membrane you should use one of the pricier ones such as versabond and not add the admix.
If you are simply setting tile with it and it does not require an unmodified go ahead and use a modified thinset which has a dry version of the admix already mixed into it.
Just FYI the latex or admix makes the thinset a bit more flexible so the bond does not come loose with regular seasonal changes or heavy traffic. If you are just setting tile I would use a modified thinset.
Roger,
I need to re-grout the bottom of my shower stall, perimeter only, on all 4 sides. The bottom row of wall tiles are coved on all four sides, where they come down to meet the floor tiles. I slowly, carefully & successfully removed the broken grout and vacuumed the 1/8″) grout line. I know how to grout –the issue is that I need so little and I am NOT finding the suitable product that comes in less than a 10 lb. box or bag!…except that I saw this product by Custom Building Products in Seal Beach, CA, in a local hardware store. It contains in this order: Silica quartz, C.A. S. 014-808-60-7, Portland Cement, C.A.S. 997-15-1, and Polyvinyl Acetate Copolymer. Only instruction is “mix with water” and it is called “2SET Tile Repair Mortar.” The only problem is the pound size container lacks any usage statement for or against use on a shower floor, while 99% of the other products, whether at Home Depot, OSH or wherever say “not for use below the waterline.” Just try to get someone on the phone at Custom Building Supply who isn’t chewing gum and sounding like a 14-year old! Email did not work either–they are in need of some web admin assistance! Does this product sound suitable for the bottom of the shower as long as I wait for three days after grouting and then seal the grout lines? I have the tools necessary to install it, if so. Thank you.
Hi Barbara,
The product you are looking at is a tile repair mortar meant to adhere tile to a substrate, not to be used as grout. Other than the color probably being nowhere near what you need, it will not be really suitable as a grout replacement. It will work, I just don’t recommend it. You should be able to find a regular sanded grout in a five lb. box at either Home Depot or Lowe’s that is specifically what you’re looking for at a reasonable cost.
I totally agree with what Roger is saying.
those 2 pails of premixed will cost more then 2 bags of Versabond or another good $15 bag of modified thinset. sometimes it’s just not worth paying more to get something done faster.
mix less dry thinset and mix what you can use.
Hey David,
As long as you are using it in a non-wet area such as a backsplash, wainscot, or fireplace you will be fine. If you’re tiling a shower wall do not use that product. Use regular thinset.
If you are talking about using it on a floor – no, it is not suitable.
Read the bucket, it probably states not to use it for tiles over a certain size – probably 8 x 8. As I stated it would be just like putting the lid on the bucket.
Pre-mixed is easier than mixing. Would you rather save a couple of minutes of installation time or a couple of years of project durability?
Is there no use for premixed thinset? I’m tiling a small area, and a bucket or two of nice premixed latex-modified thinset seems a lot easier than mixing.