What is the difference between modified and unmodified thinsets?
Which unmodified thinset is better?
What makes a modified thinset modified?
Why do you drink so much beer?
These are questions I get asked a lot, along with ‘why is my dog on fire’ (because you used the incorrect product for a specific installation).
Unmodified thinset is simply a thinset which does not have any latex polymers or other products added to it. It is essentially portland cement, silica (sand) and lime. Recipes vary, but those are the basics.
History (pay attention – there may be a quiz…)
To understand modified and unmodified you should understand why modified exists. Way back in the 1940’s Henry M. Rothberg was a chemical engineer. Back then the standard installation procedure for floor tile was the full bed method. This was a 2″-3″ deck of portland cement and sand upon which tile was installed. The need for the thickness is at the heart of the development of modified thinsets.
It needed to be that thick in order to retain enough moisture for the cement to fully cure.
Concrete cures through a process called hydration. The cement chemically reacts with water and grows interlocking crystals – these interlocking crystals are what gives cement it’s hardness. These crystals grow as long as they are exposed to moisture (water). Once the water is gone the crystals slow and stop. So…
The longer the cement is exposed to moisture the longer the crystals grow. The longer the crystals grow the more they interlock. The more they interlock the stronger the concrete.
It’s all about moisture retention in the mix. Enter Latex (or rubber). Rubber was added to concrete mixes in the early 20’s to repair and solidify sea walls, and later added to brick mason’s mortar to make brick installations stronger. Adding rubber or latex to cement mixes helped the mix retain water for longer periods of time.
Mr. Rothberg realized that the common tile installation methods at the time had limitations. He set out to find a way to solve this. He began experimenting with the natural latex which was being used in sea walls and brick work but soon realized the these products had limited working time and were difficult to store for any amount of time before degrading.
He then set out to develop a synthetic form of latex which would be easily stored for longer periods and had an extended working time in order to be feasible for tile installation purposes. After developing and testing more than 300 different chemical compositions of synthetic latex rubber he finally found one that met his criteria.
It was introduced to the market as ‘Laticrete’. It was a liquid latex polymer which was added to concrete mixes to make them stronger and give them some flexibility.
That’s right, my favorite company actually has a story. The name is a pseudo-compound word formed from ‘latex’ and ‘concrete’. This was the name of the synthetic polymer Mr. Rothberg created for use in tile installation products in order to retain moisture in the mix and allow it to cure stronger and not be as brittle.
In the 1960’s the (then) Tile Council of America developed a powdered thinset with dry polymers which were activated by adding water. Soon afterward it was used by nearly everybody for nearly every installation. This actually led to a lot of problems, mainly due to misunderstanding of the product and it’s limitations – it was being used for everything with unrealistic expectations.
The latest modified thinsets have come a long way from the original TCA types and are now tested to minimum standards in an attempt to keep expectations realistic. Powdered or liquid polymers added to regular thinsets help the mix retain water for a more durable end result, as well as adding flexibility, bonding power, or any number of specialty capabilities needed for the numerous installation requirements.
Any thinset that has either a powdered or liquid latex polymer added to it is considered a modified thinset. Any thinset that does not contain these is an unmodified thinset.
This post began as a description and information on unmodified thinsets and which are better. I realized very quickly that this was not a subject that can be easily explained in one blog post. It can – but you’d get bored. So my next post will deal with that topic now that you know why modified thinsets exist and what they do.
I am installing 13×13 porcelain tiles and glass/stone mosaic accent over hardiebacker in a tub surround. Which Mapei thinset would you recommend ? After reading your site, I thought I knew what to buy until I was stumped by the multiple choice quiz in the aisle. How many variations are really necessary???
All the variations are necessary. There are a LOT of different applications for different installations. Ultrflex 2 would likely be your best bet for your installation.
I’m going to tile my bathroom shower using 12×12 tile on the walls and olive pebbles mesh on the floor (wife’s idea). will also be tiling the floor with ditra and 12×12 tiles. I know now that I should use unmodified thinset between the ditra and tile, but can I use unmodified between wood sub-floor and ditra? also, would you recommend unmodified for the shower wall tile with a backerboard as the base?
You NEED to use modified between ditra and plywood. It’s necessary. Unmodified will not last. Unmodified everywhere else, including the shower walls.
Hi people I’m a small contractor here in LA I was remodeling a old 200 unit apartment building
With a raise foundation my tile contactor cleaned the old sub- floor uplyed red guard and installed my 18″x18″ porcelain tiles with modified thinset
It’s been 3 years with heavy traffic and no problems. Please give me any feed back thank you.
Not sure what type of feedback you’re looking for. If all that tile is over a concrete subfloor then it will be just fine, that is an approved installation method. If it’s over wooden subfloor it may last – it may not. No real way to tell until it begins to crack the grout.
I’m re tiling my bathroom with12″x24″ tile. Over an area of 30 sq ft. I Installed a new subfloor but ended up with a high spot at one end of the tub, creating a low spot near the centre the floor of about 5/16 inch at its deepest. I plan on using Ditra.
My question; can I float some thinset to even out the floor, let it dry and then install the Ditra? Or should I use something like SLC instead? (I’m trying to keep the floor height to a minimum)
Btw I’m using Kerabond.
You can float it out with thinset first beneath the ditra.
254 between ditra and plywood and 317 between tile and ditra? Good to go?
Thanks for this post. A very informative read. But one thing I’m unclear on: the old bed system for tiles makes sense to me (i.e. the need for thickness to retain moisture), but current non-modified thinsets don’t need to be thick at all to work well. So what is different between the older mortars and un-modified thinsets? I would have guessed they put some lime in it, but they have been adding lime to mortars for a long, long time for this purpose, and expect they would have done so for tile long ago.
Any info is appreciated.
There is no difference. The difference is in the applications with which unmodified thinsets are currently utilized. Using it over things like ditra and kerdi allows the mortar to retain the moisture, as it has no place to dissipate while curing.
Roger, I am lucky to be able to get Ditra set for my kerdi board wall tile application. I am doing a regular mud pan and was wondering if it was you would you opt for a modified thinset for those tiles on the mud pan.
Probably not, the unmodified ditra set will work just fine. It’s a very good thinset.
Roger, Great info here and I really appreciate your humor. I’m putting down porcelain 16×16 tile in my garage over tenter year old concrete that is in very good condition. Can you recommend a thinset and any other advice that I should be aware of? This garage will never have freezing issues or water other than when cleaning. Thanks.
If you’re going directly to the concrete I would use Laticrete 254 or mapei ultraflex 2 or 3. I would also recommend a membrane such as ditra, but it isn’t necessary, just a bonus.
Thanks for the quick reply and advice. I read your blog on ditra and priced it out. That is pretty pricy. There are expansion cuts in the floor and was wondering if it would be wise to use the ditra if only over the cuts so that those tiles are floating and the others would be set to the slab? If I did that, would that 1/8 difference on those tiles be tough to deal with?
Mapei advices that I use their ultraflex lft with a 1/2X1/2 notch. Are they just trying to up sell me?
Well, kind of. But only in the sense that the ultrflex lft will solve the problem. It is non-sag medium-bed, so you can build up as much as you need to compensate for the inconcistencies.
They would be nearly impossible to deal with. You can use a crack suppression membrane of some sort over those joints to deal with them, redgard is actually a very good one. You do, however, still need a soft joint over every one of those expansion cuts.
Great site, first time seeing it and i see alot of useful information and you seem to really know your stuff..
quick synopsis, installed a Tile Redi shower pan thats pre slopped and leak proof, im using their special epoxy included with the shower pan to set the floor and it set up very well. I also purchased the additional flashing kit system with it, the very thin piece of aluminum hangs inside the shower pan aproximately half inch. The way its designed, it appears it has to be like this. My questions, when tiling the side walls should i go over that little bit of aluminum with their epoxy or the modified thin set that im using for the regualr wall tiles? Im afraid one or the other wont adhere to that aluminum. Have you ever used this tile redi shower pan product? Any thoughts on it? Thanks and have a good day.
Yes, I’ve used it. It’s a good product. At the bottom of the wall you don’t use anything to bond the tile to the aluminum, it just sets over it. The epoxy will bond to it if you want to do that, but no real need to. Thinset will not.
I installed durock membrane over 1/2 in durock in a tub surround with the durock membrane adhesive. I now have some bubbles that I cannot get out on the outside corners. Should I cut them and add more adhesive then put a patch over it? Also the store says to use unmodified thinset for the ceramic tile and usg literature says use a modified thinset which should I use?
Yes, cut a slit, add more adhesive and patch over it. You need to use modified thinset with that membrane.
Roger, I want to do kerdi boards on the walls and am wondering if a do it yourselfer can tile well with unmodified thinset. Is there anything I should be careful with on the installation and do they hold the tiles as well as modified?
Yes, you can. As long as it’s a good unmodified then there is very little difference when working with it compared to a regular modified. And yes, they’ll hold the tile just as well.
I bought 252 silver laticrete thinset, and i’m using 12×24 tiles with mosaic strips on all sides inbetween each piece. I was reading today that its better to use a medium bed thinset for larger tiles. its for my shower. Whats you thoughts? should I use a different thinset, and if so should I use it on just the 12x24s or on the mosaic pieces too?
It is normally best on floors, what you have is completely fine for the walls. Medium beds prevent sagging (sinking) of tiles as it cures, problem for floors – not walls.
I have always used modified t-set for all my tile projects knowing that it is highest bonding to porcelain. I’m using that ditra mat stuff for some dumb reason, now they say you can only use non modified t-set that I am dead against because of the movement issues and bonding to the tile. Do I use modified and just let it sit longer before I grout it to let it dry longer or:?:
Yes, you can do that, or you can fill the waffles with unmodified, let that cure, and set your porcelain with modified. Either way you’ll lose your warranty. But they’ll both work just fine.
Can I use mapei ultraflor white mortar for setting 2×2 mosaic marble tile in a shower stall.
Yes you can.
Is there different classifications/levels for unmodified? Or are they all in the same boat?
Modified can be described in 14 different ways with ISO new classifications. C1 C2 then a few additional factors.
They don’t yet have different classifications for unmodified, I don’t know that they ever will since schluter is about the only manufacturer that demands its use.
Thanks for all the cool and informative reads! Love the jackassery.
Just a quick question regarding thinnest thickness. I know it’s called thinnest for a reason, but is it possible to use TEC (modified mortar for porcelain tile) to build out a wall 3/4 of an inch? Meaning, I have 3/4 inch gap where tile ends and the perpendicular wall starts, so I need to fill in 1/2″ of “stuff” and then 1/4″ of tile so it comes up flush to the already tiled wall. Should I use thinset as the “stuff” or 1/4″ extra backerboard?
Thanks a lot!
You should use 1/4″ backer. 3/4″ is WAY too much to build out with thinset.
I’m getting ready for a master bath renovation and will completely tear out and rebuild shower and re-tile the floor. I’m planning to use glass mosaic for 2 shower walls, a third wall will be created by butting up to tub with glass on top and the 4th will be the glass door entrance.
I purchased Mapei Ultraflex 2 (white) at the recommendation of the local store seller. Is this good for both shower (glass mosaic walls and 2″ travertine mosaic floor) and bathroom floor (3/8″ polished travertine) or should I try to find Laticrete or something else? I will also have a preformed plastic 12×24 niche to install with shelf inside. Any special thinset to use to adhere to plastic? Rough up plastic first for better adhesion?
The grout is also Mapei, but I don’t remember exactly which. After reading your blogs, I now know that I will need to find matching caulk for sealing changes of plane and leaving weep holes above tub.
Thanks for everything!
Yes, the mapei will work for all of it, it’s good stuff. The particular manufacturer of the niche will tell you what you need to use to bond tile to the niche. You did not say what brand it was, so I have no idea. Some require epoxy (and usually is included) and some work fine with regular thinset.
Sorry for the delayed response, my spam filter went ape shit last week for some reason, I just found your comment in the spam folder, I hope the answer found you in time.
Hi Roger, We are getting close to tiling our shower surround. Redundant questions follow:
1. Since we are using redgard , do we still need to silicone the hardiboard screwheads in the shower surround?
2. We are taping and thinsetting the individual planes. How long do we have after that until we can redgard?
3. We are using porcelain or ceramic mosaic, mini- subway tile about 2×5 pieces on 12×12 netting. We have simpleset pre-mixed, thin-set mortar (custom building products) white. It consists in this order; water CAS 7732-18-5, quartz sand CAS 14808-60-7, acrylic polymer CAS n/a, calcium carbonate CAS 1317-65-3, titanium dioxide CAS 13463-67-7, ethylene glycol CAS 107-21-1, stoddard solvent CAS 8052-41-3. This thinset was bought in a 1 gal bucket from HD. It only says it exceeds ANSI 136 Type 1. Since we have a cast iron pan , is there another hd product you might steer us toward or will this be the best for 1st time DIY’ers.?
Thank you as always. (My elderly head is spinning , but I think non- modified might be beyond our level. Right?)
Ooops, ANSI A136.1 Type 1.
Hi Roger, I just called the the tech support of simpleset premixed thinset. I was told to get Versi-bond instead of simpleset. They said the simpleset is not to be used with redgard.
Will you please confirm that? They said to mix it to a mayonaise or peanut butter consistency and it would have a 3-5 hr working time.
Yes, I just said that.
2. 24 hours
3. You want regular modified thinset. DO NOT use that premixed stuff. It actually isn’t thinset at all, it’s mastic with sand in it. It will NEVER cure between the tile and redgard. It is easy, just take your time with it.
You are a saint or should be sainted. I feel a bit empowered that I can actually read comments on other sites and know what is absolutely not advised. Will try to send pics when we finish. In our demo we did before we got this far, we learned a lot also because of your instructions.
Hi Roger, I love your site. I have been reading bits and pieces over the past 5 months while tearing out my kitchen and I am finally ready to tile. Today I bought ditra, tec unmodified, laticrete grout, tec grout boost, and laticrete modified gold. Problem is, when I got home I realized they loaded me up with the gold rapid set. I’m a first time tiler (tileist?) and the rapid modified thinset scares me. Should I take it back and get what I ordered or will it be fine? Thanks again for everything!
I would take it back. The rapid set works well, but you have to pay CLOSE attention to the times. When it sets off there is no working with it. It depends on how comfortable you are with it, I would get the stuff you ordered.
Can I waterproof the thin set i used to level off my shower? I do have a pan, as well as quick create than motar and pebble stone which was grouted poorly so I’m going over existing floor and my wife likes the look of the thinset is there a clear coat or waterproofing product?
No, thinset is not a wear-layer. That means it will degrade over time if it is not covered with a proper tile.
Great site, and you obviously know your stuff.
Ass kissing aside, also being a Fort Collins guy, would like some advice on where you get materials. Can’t find Hydroban anywhere locally. Looks like HD has Redgard.
Looks like Lowes has Mapei for mortars. Best choice?
Tearing out a not so well done second story double shower with a custom cultured base. Planning on porcelain field tiles with glass mosaic waterfalls under the fixtures.
Does the lightweight concrete backer board perform as well as the others?
I order it online or get it from Design Materials down in Denver. Yes, the lightweight stuff is very good and lasts just as long.
I need to do some leveling for a shower base and using 3/8″ 13×13 porcelain tile:
a) level shower base by 1/8 – 1/4″ in some spots. Am I going to run into trouble building up the shower base by 1/4″ with thinset? Tile/thinset will then be installed on top of this.
b) raise schluter profile by 1/4″ on one end so it is level with other part of the shower (i.e., drain). I plan to use plastic horseshoe spacers under the profile to maintain the proper height while I the profile in thinset. Is this the best way to raise the schluter profile to a level point? I like the plastic spacer approach because it seems more precise, but should I instead be using something like pieces of hardi-board?
I am using a TEC medium bed thinset.
With the Tec medium bed you can build up to 1/4″. And yes, the horseshoe spacers are the best method I’ve found, I use ’em for everything!
Thanks Roger. Just to clarify, I need to build 1/4″ and then I will have additional layer of 3/8″ trowel to set the tile. Will I be ok or is that too thick for thinset?
Also, I have one spot under schluter profile where I need to build 4/16″. If yes to my first question, can I go this extra 1/16″ without getting into trouble?
Yes to both with the TEC.
I can’t find laticrete my tile store recommended prospec permaflex 600
will that work?
Yes, good stuff.
Long before I saw your blog Lowes sold me their expensive $50 tub of TEC Universal mastic and I used this stuff to tile walls above a tub ~100 ft2 using 9×12 ceramic tiles.it. It was easy to work with and I also used it to seal the fancy alikali resistant mesh tape over the backerboard seams. This stuff was so sticky that it was hard to pry off a tile after 2 minutes. I now know that mastic and floors and shower walls and floors are a no-no, but this Universal stuff was supposedly approved for shower walls (as it said so in the literature). At any rate, the stuff worked great and the installation turned out great (and no issues in 4 months of heavy use). OK, let me have it… What kind of problems, if any, am I looking for with this stuff or is it a RDWHAHB?
You may be perfectly fine, and it may fail in another year. I have no idea and there is absolutely no way to tell until if fails. I would make damn sure you have weep holes in your tile at the tub so that water getting behind there does not stay in place emulsifying the mastic.
yes, I did do weep holes. Do you caulk where walls meet?
I used spectralock where the walls meet b/c of the color stability (no mold, mildew, etc…) and b/c those lines are so long – please say this was OK
The bottom of my curb front starts on a hardwood floor. I plan on using a spacer between the floor and the first tile, can I grout that space or do I have to use caulk? Can I grout all four continuous horizontal 1/8″ lines on my curb?
BTW, is there a reason that my tile brand makes the bullnose 1/16″ longer than the 12″ tile and 12″ mosaic sheet? Seems like I may end up having to cut a sliver off of each bullnose to get everything lined up.
Yes, I silicone all changes of plane. They should be siliconed, they should not be grouted. It may be fine with spectralock, another one of those flip-a-coin things. You have to use caulk or silicone at that transition. Your manufacturer likely outsources the bullnose, that’s why it’s a different size.
I would like to know what thinset mortar you would pick. After I do all this prep I want a thinset that will last and hold well. The tile is porcelain 6×6 on shower walls and 12×12 mixed with 6×6 on floor. Here is what my stores have.
custom building versabond fortified
custom building flexbond fortified crack prevention #fb50
custom building porcelain tile fortified
Mapei porcelain tile
OR would you get unmodified in the brands above and add the additive yourself?
The versabond will work just fine. The mapei and custom porcelain mortars are also very good, but not really necessary with your tile size, they are more for larger format tiles.
Hi Roger, what if the above question were asked in association with kerdi fabric and pan…specifically the versabond fortified? I have three bags of it and am wondering if I should return them for an unmodified mortar, like the manufacturer recommends, or if this lightly modified mortar would work okay. I see on other sites that they say it works…
Same answer. And no matter what JB says there’s no such thing as a lightly modified mortar – it’s either modified or not. That said, versabond works just fine in my experience.
Can I used hydro ban over duroc .then set porcelain tile with modified thin set ?
Yes you can.