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.
I am replacing the glass mosaic tile along the inside top of my concrete swimming pool. Can you tell me what adhesive and grout I need? I am in Canada so it needs to withstand the winter.
Hi Brian,
Don’t know much about pools. I know you’ll want a highly modified thinset like laticrete 255 or mapei ultraflex 3. Most of the guys I know who do pools and spas use epoxy grout.
Hi Roger,
Great site, wish I found it before!
Last weekend we started glueing down 12″ black granite tiles on our new bathroom floor using “universal adhesive” that came in a bucket. Is this stuff mastic? Have I done something I will regret? What to do?
Hi JC,
Yes, it’s mastic. I would remove what you have down and scrape the mastic off of them. If it’s a bit difficult to get off you can always soak them in water, it’ll come off then. You want to use powdered thinset sold in bags that you mix with water.
Just finished removing the tiles and scraping them and the cement board. The mastic was still very soft and was pretty easy to clean off with a putty knife.
Thanks for your help. I’ll finish reading your site BEFORE I continue with my project!
Sorry you had to do that but it once again proves the point that it is an incorrect product for that application.
At least it came off easily.
Great site but not enough time to go through everything. My wife bought glass mosaic tile and wants me to install them for a shower floor. I am using schluter kerdi to waterproof the shower. What type of thinset should I use? I am using a cement board as a substrate for the walls and read not to use a vapor barrier behind it if using kerdi membrane. Is there a reason for this? I’m in Canada and vapor barriers tend to be quite critical. Thanks in advance for your advice.
Darren,
I have the same type of problem. Wife wants glass mosaic on Kerdi. Schluer (Kerdi people) said don’t do it. You need modified thinset for glass mosaic and Kerdi requires UNmodified thinset. I’m now in limbo trying to figure out what to do.
Use modified thinset. You won’t have your schluter warranty but your shower will last.
So since I already have several bags of unmodified at the house, do I put unmodified on the wall, then put up the Kerdi, then put modified on the front of the Kerdi then put on the regular tiles with the glass accent strip? By the way the accent strip is really a mosaic of tiles and includes some 1″x1″ and 1″x2″ tiles made from metal, terazzo, glass and who knows what else..pepsi?
And which modified should I use?
If it starts to peel off, is it ok to shoot a ramset through the metal tiles?
Thank you
Yes, you just won’t have your warranty from schluter. No big deal. Any of them will work.
Put a dab of silicone on your tile first if you’re gonna use the ramset.
Hi Darren,
First of all you should not use the glass on the shower floor. Not only will they likely crack eventually, they are VERY slippery. I mean like a block of ice slippery. If you insist on doing it use a good modified thinset like mapei ultraflex 3 or laticrete 254 platinum.
If you have a vapor barrier behind it you create two waterproof barriers with the substrate in between. Any moisture or vapor trapped in there can not dissipate, it is a breeding ground for mold.
Hi Roger,
Thank you very much for your prompt reply. I’m going to go out shopping without my wife to find something else for the shower floor. And the vapor barrier behind Kerdi makes sense now that I think about it. Imagine how bored you would be if you didn’t have to think for people like me…
And I read “Real Tile Pro’s” comments on About.com. Sounds like someone is pretty jealous of your expansive knowledge.
Thanks again.
Hi cCD,
Who in the hell told you to use acrylpro??? Let me guess – HD employee? Ummm, that’s wrong – but you already knew that. Versabond will work, but the marble and granite mortar, being a medium bed, would be ideal for that.
Medium bed mortar does not sag or shrink as it cures. Your tile will stay where you put it.
Acrylpro, while not *technically* an organic compound, is still considered a mastic in regards to tile products. And it WILL re-emulsify when exposed to water for a long period of time. Water WILL get behind your tile and grout, it’s just a fact of how showers work. Your tile and grout are not waterproof. When water gets in there, it sits there until you shower again. This is not considered ‘intermittent’ water exposure – it is constant water exposure.
The humidity or lack of in your particular part of the country has nothing to do with mastic not curing. Think about it like this – your acrylpro is in a bucket – with a lid. Once you open it and use it you replace the lid on it. The acrylpro remains pliable and usable in the bucket, so long as it’s covered. Putting it on a wall, over a waterproof substrate, then putting a large tile over it is just like putting the lid back on the bucket.
The limitations portion of acrylpro’s data sheet states:
“Do not use for steam rooms, showers, underwater or areas exposed to hydrostatic pressure.”
Showers have hydrostatic pressure behind the tiles.
You can, of course, use whatever product you choose. I highly recommend against using acrylpro for your shower – the above reasons are why. Here’s one more – nearly every shower I tear out which was set with mastic has mold, saturated wall studs and re-emulsified mastic behind the tile. It’s not pretty.
Hi Roger,
I installed a fiberglass tub 1″ from an existing porcelain tile floor and filled the plywood substrate floor gap with silicone caulk. It doesn’t look so good so I am thinking about covering that gap with a row of 1 X 6 Daltile ceramic pencil trim. The outer edge of the trim would rest on the porcelain floor, the other directly on the tub. How can this be done without removing the silicone caulk and what combination of thinset, grout and caulk would work?
Thank you very much,
Suzanne
Hi Suzanne,
You can’t use anything that will last without removing that silicone. Once you do that you can just fill that gap with thinset and bond them with that.
Roger, thanks to your excellent advice in general and answers to my questions, I’m about ready to actually tile. I’ve laid in a supply of chocolate milk but have two (hopefully, only two) remaining questions. Somewhere, in your postings I think I read that minimum grout distances were 1/8″ for floor and 1/16 for walls. My 12×24 rectified porcelain will be on floor and was in a grid so I’ll need consistent grout width. Must it be 1/8″?
Secondly, somewhere else I saw a medium or “med” thinset being recommended for large format tiles going on walls. Is that advisable? I’ll be sculpting buttered bullseyes per your suggestion.
Many thanks and appreciate your support of our wounded warriors. Nick
Hey Nick,
Grout lines can be whatever you wish them to be provided the tile is consistent enough to allow it. 1/16″ and 1/8″ are simply the ones I normally use.
You don’t need medium-bed, but it’s really helpful.
I have experience at putting tile in my bathroon in the shower and on the floor. I’ve never had a problem. Now I want to re-tile my swimming pool tile with Mask625new. It is a kiln fired clay product Can you tell me what kind of glue is required. How I can apply it to prevent it from coming loose or off as the bottom border will be continually submersed in pool water.
Thank you so much. If you wish to speak with me I can call you or you can call me at xxxxxxxxx. Thanks for listening God Bless and have a greaat day. George
Hi George,
I’m not familiar with that product. Is it approved for continuously submerged applications such as pools? If so your best bet would be to contact the manufacturer and ask them what product they recommend to bond it. They can give you specifics.
Roger,
When installing 12×24 porcelain floor tiles, what is the recommended thickness of the mortar? In other words which size trowel should I use? Is is also necessary to apply mortar to the back of tile in addition to the floor?
Thanks
Hi Rebecca,
Minimum thickness of thinset beneath a tile is 3/32″. That, however, is just a basic guideline put in the standards to ensure there is enough thinset beneath tile. The proper trowel is the one which gives you full coverage beneath your tile. That will depend on the flatness of both your substrate and tile. With large format tile like that I use nothing less than 3/8 x 3/8 inch trowels. It is always a good idea to at least backbutter (a skim coat of thinset in the back of the tile) all your tile. Whether or not you need to comb it on the back, again, relies on how flat your tile and substrate are.
Get a 3/8″ trowel, comb some thinset on the substrate and back butter the tile, put it down and embed it. Then pull it back up to ensure you have full coverage of thinset. If not comb thinset on the back of the tile as well.
Thank you very much!
Hi Jeff
Lady DIY here, please help,I have read so many different opinions on fasteners for 1/2 inch hardibacker on shower install. Do you recommend the hardi screws or galvanized roofing nails? Also I put in a call to Hardi customer service and they told me I do not have to allow any spacing between boards, but all the tiling forums say 1/8 inch? What is your recommendations.
Thanks Gail
Hi Gail,
I prefer to screw everything rather than nail it. When I was young I nailed everything, now I screw everything…
Wait, that didn’t sound right.
The hardi screws are the best way.
To enable you to lock the boards together with thinset and alkali-resistant mesh tape you need the gap there. Hardi also does not specifically call for a vapor barrier behind their backer, so they are in the business of covering their ass rather than giving practical advice.
That’s why I’m here.
I have a shower floor problem. My shower is now about 5 years old. Over the years the grout between the 2 x 2 floor tiles has been ozzing a sticky clear liquid. It eventually turns white and crusty. I have been cleaning it with an acid cleaner, but it continues. At first I thought it was efflorescence. Now I have some areas where the grout has worn away some and I can see a lighter colored material which is pliable when probed with a knife. It has a mud base with vinyl liner under it(I think). This shower has not been used consistently.
Does this mean that the tile guy used mastic on my floor??
Thanks
Tim
Hey Tim,
That would be my guess. The only other reasonable possibility would be latex leaching from the thinset, but that is extremely rare and usually only seen in steam showers. If it is indeed pliable it likely is mastic.
Hi Roger,
I gutted my bathroom to the studs. My house was built in 1965 so the sub floor is 3/4 x12 boards with about 3/4″ spacing between them. They are on 2×8 joists 16 oc.There was some deflection when jumping on these so I reinforced the joists with 3/4 plywood and another 2×8 sistered to the existing joist. I am guessing you will advise taking these boards up and replacing with 3/4 plywood before laying hardibacker. My question is that there was a tile floor over this substrate prior to demolition. Do I really need to pull up the 3/4 x 12 boards prior to laying the hardibacker?
Thanks for your time,
Bill
Hi Bill,
No, you can go over those boards with an additional layer of plywood (which you should do) and put the backer over that. No need to remove the existing, just install 1/2″ layer of ply over it.
Hi, Roger,
I’m planning to install glass mosaic tile directly to my 6 inch soapstone backsplash. What is the best material to adhere the tile to the soapstone?
Hi Judy,
Epoxy setting material, Mapei ultraflex 3 or Laticrete 255.
Hi Jeff
Thanks for your great site and manual which I just downloaded.
We have a ‘shower over the bathtub’ setup with all walls tiled all the way up to the ceiling which is also tiled. The long wall is an exterior wall with a fairly new window. Recently the inset ceramic soap holder/handhold completely fell out and now there is a gap full of old thinset (probably over plaster and mesh as all our walls are plaster). We were very worried that it is damp, but thinking we have a ‘traditional’ set up maybe that is normal ‘backerboard retains water’? There is no sign of mold so can we simply replace the fallen out soap holder and if so what is the best way to do it? Do we need to scrape out all the old thinset and try to get everything dry first? We only have one bathroom so the quicker we can do it the better.
thanks a million for any suggestions.
sorry Roger, don’t know why I typed Jeff, brain freeze.
No worries, I’ve been called worse.
Hi Richard,
Yes, you need to let everything dry out before reinstalling the soap dish with thinset. You should be able to see the plastic or roofing felt behind your substrate if you do have a traditional setup.
thanks a million Roger.
Opened up and dried out but the job continues, and another question (sorry). There was indeed backerboard and plastic behind the tile, but after taking a few more tiles off to make a nice cut for the new piece of hardiboard, we realized that the old installation was plastic, then sheetrock (!!) + hardiboard behind the tile. Ugh, very wet sheetrock (didn’t we read on your site NOT to use sheetrock!!) So we took out a whole big section to reach a drier area and the studs (we want to put grab rail in while we are at this). Question is to make the depth match the existing tile we will need 2 layers of hardiboard; can we just thinset between the layers?
Yes, no problem with that at all.
Hey Roger,
I’m tiling a shower surround, kerdi over hardiebacker. Field tile is 6×6 ceramic. My wife wants… er … my plan was to include a pair of 2″ horizontal strips of 1/2″ glass mosaic at eye level. However I just read in one of your posts that unmodified won’t stick to glass.
Can I use modified for these stips? and give it a couple days to cure before grouting?
BTW – Both How to Waterproof a Shower”, and “Tile Tips” have been very useful. Wish I’d read them before that “Renovation Realities” crew showed up…
Hey Rick,
Yes, you can use modified (and should) for the glass. It’ll cure overnight.
So if I’m using Kerdi and then tiling on top of it, I should use unmodified thinset behind all the ceramic tiles and then modified thinset behind the glass tile accent stripe and then unmodified thinset all the rest of the way to the ceiling? Would adding beer to the unmodified thinset be the modification I need or is there a different better modification for glass tile on thinset?
Obviously I already started with the beer. That last question should be “…is there a different better modified thinset for glass tile on Kerdi?” Now back to beer, I mean work.
I would use modified for all of it. But if you choose to use unmodified then yes, you need to use modified behind the glass. Any good modified will work with a simple mosaic strip. You CAN use unmodified behind it, but it’s really not recommended – glass expands and contracts a lot.
I know you prefer Pepsi so I hoist one to you. Thank you so much.
Roger,
My plumber installed a Tile-redi base, at customer’s request. After the shower pan tile was laid, we noticed a flat spot on the floor, and water was not draining. Rather than pull up the old tile (not sure if that’s possible!), can we tile over the existing tile? It is 2″ x 2″ Dal-tile mosaic.
Hey Steve,
You can, but you need to remove the coating of the existing tile and use a thinset specified for tile over tile installation. Mapei ultraflex 3 and Laticrete 254 are two, there are others. And no, it isn’t possible to remove a tile from those pieces of….*ahem*, from those shower bases without damaging them.
Roger,
I will have to say, we have installed several of these bases, and have been very satisfied with them. My tile installer insists (just like you) that they are no good. However, they are water proof and cheaper than a poured base. I guess time will tell if they are a quality product, but as of now – I like them!
They’re normally a good product. But if you have one like the one you have with a bad spot then it could lead to a minimum of an extra day of work, that costs me money when I can mud and waterproof a pan nearly as quickly as installing one of those. If you like them use ’em, more than one way to build a shower. For some reason about 25% of the ones my customers order come in flawed in some manner, I’ve simply stopped using them.
By removing the coating, are you talking about sanding the coating off of the old tiles – or is there some type of chemical?
You need to either sand it or scarify it enough to remove the ‘shininess’ from the top of the tile. You want open pores in the tile for the thinset to bond.
Thanks Roger – you da man!
I bought some accent tiles from wetdogtile for an oceanic theme. They recommend applying the clay made figurines directly over your tile using mastic, then applying silicone around the edges. Is this legit?
Hey Robert,
As long as it’s in a dry area like a backsplash. If not just use thinset and grout around them like every other tile in the shower.
Hi Roger,
I searched your site but couldn’t find a reference for recommended trowel notch sizes. I’m guessing that you’ve answered this many times, so sorry if I’m asking you to repeat yourself.
I’m installing 12×24 rectified porcelain tiles in my tub surround over Kerdi Board, with one vertical 12″ strip of glass tile from the top of the tub to the ceiling. What is the appropriate trowel notch size for the thin set?
If you haven’t already done so, (I couldn’t find anything), you might consider creating a reference chart for these types of questions and save yourself from repeating your answers to annoying questions like mine over and over again.
Thanks!
Hey Tom,
That is actually the subject of my next post (when I get some time…)
With that tile I would use a 3/8″ u-notched trowel. Provided your substrate and the tile are mostly flat that should give you the coverage you need.
How ’bout that, brilliant minds think alike. I’m usually thinking about beer.
Forgot to ask another question. I read somewhere that it’s best to back butter porcelain tile. Is that recommended in my application?
Thanks again!
Yes, all tile should be back-buttered in my opinion.
Do you have any thoughts about how I would go about setting a penny tile floor made of actual pennies? They’re so thin that a thinset won’t work (not that there’d be any bond from it anyway, to metal). I can’t come up with a method that I trust will hold up.
Hi Aaron,
Epoxy setting material with a vct notched trowel.
What do you suggest for thinset, modified or unmodified, to put 20 x20 tiles on the concrete subfloor? We have unmodified Kerabond left and wondered if we can use it alone? Or do we need to add an additive like Mapei kerelastic (sp?) from Lowes? Or do you suggest something different?
Thanks
Hey James,
The kerabond will actually work fine. I would let it cure a full 24 hours, but it’ll bond just fine. You can also use nearly any good thinset for that installation.
Thanks. Another question-Does it matter how long I wait to grout? The tiling may take me a while doing it after my paying job each day.
Day jobs suck.
Well, mine doesn’t, but you know – most. They get in the way of stuff you wanna do!
As long as you wait the full cure time for the thinset it doesn’t matter how long you wait before you grout. Just do it all at once when you’re done, it doesn’t need to be put in there in any specific time frame.
I will be installing 3″x6″ white gold onyx on shower walls. Substrate will be 1/2″ Durock backed by 4 mil poly on studs and insulation (for soundproofing). Can I use a multipurpose polymer modified thinset mortar such as Laticrete 255 to install the onyx? BTW, the onyx appears to have a resin backing, maybe with fiberglass threads…not a mesh. Thanks in advance for your input.
Hey Bob,
If it is resin-backed it needs to be installed with epoxy. That said, the 255 may work, but I don’t know, it depends on the stone. Standards, however, dictate epoxy setting material with any resin-backed stone.
I am replacing tle in my swimming pool area. should I use a specific thinset for pools or just a modified thinset with addative in it?
Thanks
Hi Jody,
Yes, but it needs to be a thinset mortar approved for continuous water submersion. Laticrete 254 and Mapei ultraflex 3 are the two of which I am aware. Make sure it’s approved for that and you’ll be fine.
Thank You very much
I will see if Lowes carry one of these
I installed glass tile over Kerdi board using unmodified ANSI A118.1 thin set. As I was cleaning out the joints half of the glass tiles popped off. The back of the tiles have a decorative coating that show through on the front. There is NO thin set adhered to the tile and the wall is fully bedded. Should I have used modified thin set which Schluter does not recommend? How do I get the thin set off the Kerdi Board without damaging it?
Hey Matt,
You can’t use unmodified with glass tile. Schluter does not recommend glass tile over their substrates. That’s why. Use modified. Scrape it slowly and carefully.
Hi. I am tiling a shower with 2×2 ceramic tiles on the floor and 16×16 ceramic tiles on the walls. What type of thinset do I need to use? the walls are cement board and the floor is a mud pan.
Hey Jeff,
Any regular modified thinset will work fine. If you have a home depot near you versabond is good. Mapei ultraflex 2 or laticrete 252 if you have a lowes.
I am considering tiling the bathroom in my cottage. I am concerned about the temperature change. We close the cottage for six months every year. That means no heat. The temperature can get to 20 degrees. Would your recommend not using tile and what adhesive if tile is OK. Thanks.
Hey Wayne,
That temperature, once the thinset is fully cured, won’t be a problem at all. I do outdoor bbq’s here and the temp can drop below -10. As long as you have it above 60 for 30 days after the tile is completed it won’t be a problem. Any good modified thinset will work fine, I prefer Laticrete 252 or 253. Pay close attention to the need for expansion around the perimeter as well as installing soft joints every 8-10 feet in each direction as you would on an exterior application.