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.
Schluter advises against using modified with their products because, as I understand it, modified will take forever to cure. Or something. Anyway, I’m doing a shower, and on the durock I have applied Mapei aquadefense. I have set 12×24 tiles with modified ditra set using a 3/8×1/4 trowel and back troweling the tile as well. So to my question: How is it that modified ditra set will cure under these conditions but not with in conjunction with a schluter membrane?
Hi Matt,
It will cure with the schluter membrane. There is no negligible difference in how a modified will cure with either product. That’s about all the details I’m willing to discuss because I could (literally) go on a rant for hours over this. With kerdi you are correct in your assumptions, you are getting into the politics of a corporation’s views which MANY of us professionals continually question.
Hi Roger,
I am setting a Redi Tile base today and many are saying o use Versa Bond Mortar. I have a Lowes near me. What product is similar . . . or should I travel?
Thank you!
Hi Adam,
Last time I checked an epoxy setting material is REQUIRED to bond tile to the tile-redi pans. Call them and confirm, but I don’t think regular modified thinset will work.
Awesome advice & info. I lol’d at your humor too. I psyched to get my bathroom done. FYI, your inventive term “pseudo-compound word” actually has a term already- it’s called a “portmanteau”, when you combine chunks of words without hyphen (but not whole words). You know. Like… “Jazzercise”. *mocks jazz hands*
See https://en.wikipedia.org/wiki/Portmanteau
Thanks Andrew!
Hello, in addition to trying to figure out the best gout, installation and color I just came across unmodified thinset concerns. My master bathroom will be white marble basket weave tile and 12×24 white porcelain/white Quartz top (quite heavy). I’ve read that unmodified white thinset is best to use with white marble to resist staining. Though I just noticed 10 bags of modified in my living room. ? Will this be an issue?
*grout
Hi Anna,
It depends on the particular brand and type of thinset. Many are actually now approved for use over ditra, however, you did not state that your substrate was ditra.
Hi,
I’m remodeling a 2nd story bathroom in a old house. I plan on putting Ditra on the current subfloor/sheetrock and to tile over it with large format tiles.
My problem is that the floor slopes to one corner – enough that it needs to be corrected. I plan to self-level the floor with Mapei Floor Leveler Plus after using their primer on the subfloor. Because of the significant slope the entire floor does not need to be covered with the self-leveling cement. Once cured, I will the adhere the Ditra to the leveled floor (which will now have two different surfaces) with Customs Flexbond Modified. My question is whether this is an acceptable solution for a Ditra application.
Hey Roger,
So I’m doing a tile project for my mom. And she decided to enclose the 2nd story deck, and wants the floor tiled. When I got here, there was already 3/4″ plywood down on the deck, and 1/4 hardibacker on top of that. The bottom of the deck has insulation put in, but we are in a climate the freezes in the winter and can get quite humid in the summer. Was going to do modified to bond the ditra to the hardi, and I thought that even with the longer drying time, that modified on top for 18″x18″ ceramic tile might be best since the deck might not be completely stationary as a slab or house floor. Thoughts? Thanks so much!
not sure how old this thread is but my question is I have an unmodified mapei gray dry thinset that I usually use to lay ceramic tile. I am now laying porcelain tile and is says to mix with a polymer additive for porcelain. Seeing as I don’t want to buy a whole jug for each bag is it okay to mix a little of the additive with water, as I want to give it at least a little more strength but stretch my jugs out to 2 or 3 bags
Hi Jason,
What you want is a modified thinset. You can mix just a portion of the admix with it, but I don’t know how effective it would actually be. It would be better to just buy a bag of modified thinset.
Hi Roger,
I am new to your great site, and apologize if my question is too off-topic! Here goes:
For my crazy outdoor (i.e., in the weather) porch project, I wish to adhere 1×6 PVC boards to a substrate that is 3/4″ plywood covered with 6 oz. fiberglass cloth set in epoxy. The area to be covered is about 6′ by 20′. What adhesive should I use? I am considering 3M 5200 but would prefer something trowlable.
Thanks in advance!
Hi Art,
Google Latapoxy.
I want to lay 24 inch tile on the second floor condo of an older wood framed building .the installments ate soft and I am concerned that the tile will crack?
Will modified tho set make the floor hard enough so that the tile does not crack?
Thanks
Hi Susan,
No, your subfloor needs to be sturdy and strong enough for your tile installation. Thinset is only to bond tile, it adds nothing structurally.
Hello Mr. Elf,
What’s your thoughts on tiling over Gold Bond XP Model # GB81000800
mold and moisture resistant drywall?
I want to use this in my bathroom in all non-wet areas from the floor to the ceiling. The lower half of the dry wall will have a ceramic chair rail, glass and marble mosaics, then subway tiles underneath that.
I’ll be using Customs flexbond for the thinset. Do you think that the drywall getting the tile work needs to be painted first?
I don’t know how that purple mold and moisture resistant paper will react to thin set.
That would be fine in non-wet areas. No, it doesn’t need to be painted first.
What type of thinset for the shower floor? I’ve been shopping at Home Depot, so they have Versabond products. Unmodified? Polyblend? Thank you.
Hi RS,
Versabond is fine. You don’t need unmodified for anything and polyblend is grout, not thinset.
Hi roger,
Finally an excellent article on the Internet!
Thanks. Herm Bed.
Oh yea Mr. Elf, in all the excitement of maulin and brawlin when I was typing my post to yer, I meant to ask you about your thoughts about Custom Building Products versabond over the hydro barrier, will it stick to the water proofing membrane in your opinion?
Yes, it will bond VERY well.
Hey err…rocket scientist…whoops Elf, I intend to use Laticrete hydro barrier over the CBU (Durock) in my alcove shower which will be tiled from ceiling to cast iron shower receptor. Here’s a list of my demands….whoops err. ..questions.
)
1. Can i use liquid nails on the face of the framing 2 x4’s if they are not level, then place the CBU over it while it is wet, thus allowing it to dry to the back of the CBU? (I think i I got this from you
2. I have a couple of tubes of KBRS Polyurethane Sealant, I want to put in the corners and gaps of the CBU, what do you think?
3. If #2 is ok, then do I still have to put thinset over the gaps and change of plane with mesh tape?
4. (You now might be wantin to git yourself a big ol mug of grog and some aspirin
). So many opinions on this one. Do I need to place thinset under the hydro barrier at the gaps and change of plane, or do I simply paint the hydro barrier in the corners/change of plane, embed the Waterproofing Membrane Fabric into the wet HB, then paint more HB over that and let it dry? Entire CBU will get HB.
Some people say that the HB and fabric are enough, and no thinset is needed to make this into a monolithic structure, but what about seasonal movement of the wood framing exerting force on substrate? Will the Waterproofing Membrane Fabric and HB compensate for movement (I know it has anti-fracture properties)?
5. Lastly….there’s always a lastly Elf
. Hydro barrier over Durock or Hardie backer? I saw post online, where some people complained about Redgard not sticking well to Hardie that had been damp wiped clean, they advised cutting it with water first to thin it, paint that thinned coat first, then use the rest of the unthinned Redgard as finished coats. How do think Hydro barrier will fare over Hardi, I know it is about opinion, but your guesses are more accurate than most people’s absolute truths (little butt kissing there 
.
Fare you well Elf, If yer ever find yerself in a moldy old bog and see some beautiful tile work there, it’s all because of you.
Hi Ogre,
1. Yes you can. And yes you did.
2. I think that’ll be just fine.
3. Yes.
4. You can do it either way. I prefer it with both, the thinset creates the monolithic structure, and the mesh and hb waterproof it.
5. You can do a 50-50 mix for your first coat as a primer, once that cures just go straight with hb.
Hi while having my flooring installed the flooring installer broke a hot waterline. He said he was able to catch 10 gallons of water while it was spraying everywhere and before his helping shut off the water in the basement. He had thin set on when he broke the pipe. I’m really concerned about mold growing under the thin set and my new plywood subfloor and exterior treated osb. I had a previous water mold issue with just vylne and osb. Someone said thin set is alcohline based and I didn’t need to worry about mold growing. Is that true?
Than you
Hi Rose,
Yes, it is true, but not because of the alkali. Portland cement is a hyration-based cure product, which means that it will actually use the water. If it’s soaked then it should be allowed to dry out before continuing, but what has happened is not going to cause mold unless any wood was saturated and not allowed to dry out.
Roger,
I’m installing subway tile that’s 4×16 I’m curious if I should use a 3/16 V notch trowel or stick with a 1/4 square trowel? Also I’m planning on using a mapei mastic for the shower walls. Will that work? Thanks roger!
Hi Andrew,
No, you need a minimum of a 5/16″ square notch – that is a large format tile. And no, you can not use mastic on it, you need thinset or a medium-bed mortar.
Hi Roger,
I have learned most of what I know about tiling from your site and e-book. I just have one question that I can’t seem to find the answer to, and I’ve done many google searches on this: is there a modified thinset that I can apply directly over non-water-soluble adhesive residue on smooth concrete?
So far the internet says NO I can’t do either of those things, I have to roughen up the surface and remove every last bit of glue residue…. but I’m not sure I have all the right info because when I took up the tile in my kitchen and two bathrooms, I found that it was put right on top of the super smooth concrete and was glued down just fine. How is this possible if every site I’ve gone to says you have to use a scarification machine or something similar for the stuff to bond?? Seems like it adhered fine for 15 years without having done that.
And the glue — it’s a brown wood glue that was under some hardwood floors, took me 3 weeks to scrape up because the contractors who did it seemed to just drop it onto the floor by the bucket, straight onto the concrete, and slapped some wood on top of it. Some places had huge puddles of this stuff, which actually ended up breaking 2 different machines from Home Depot. The most horrible job I’ve seen, but it’s up….. well, mostly. There are lots of thin patches that are like glue stains on the concrete that simply won’t come up. So again, my question is, is there a modified thinset that I can use on top of this with my porcelain tile? Or do I need to get another machine to rough up the concrete and get rid of the stains? If possible, I would like to avoid another expense and more days since it has already been several weeks since we started
Thanks so much!
Liz
Hi Liza,
Your concrete needs to be able to soak in water. If it does not soak in water within 30 seconds when you splash some on there then the thinset cannot achieve a proper bond. It would be easier (and cheaper) to scarify it. There are thinsets out there that will bond to it, but they are EXPENSIVE – like $75 for a 50lb bag that will do about 80 square feet. Laticrete 255 multi-max is one of them.
I don’t know why it lasted that long. I can’t guarantee a failure, I can only guarantee methods that will not fail.
I’m installing 2×4 travertine subway tile that is mesh backed in 12×12 sheets as a backsplash. Product specifications says to install using a latex modified thinset mortar. I bought Versabond polymer fortified thinset which states that it should not be used with tiles having resin backing. What do you suggest? Tile will be installed on painted drywall.
Hi Les,
If the tile manufacture recommends modified thinset then the versabond should work just fine. In this case (as most) it is the tile manufacturer’s recommendation you should follow.
Hi Roger,
Great blog and I like beer too.
I have a 128 sq. foot exterior Deck over a bedroom below.
I installed 1-1/8″ plywood floor underlayment and plan on installing Ditra and then 16×16 inch. porcelain tiles.
Around the perimeter, there is from 2 to 4 inches of soldered, metal flashing (and also around the deck posts) installed on top of the plywood and plan on putting the Ditra membrane over it. My question is:
Should I use a polomar, modified thinset since it will also be on metal flashing and wood or a special epoxy thinset like Laticrete-Latapoxy waterproof flashing morter?
Thank you,
Kevin
Hi Kevin,
You need to use epoxy. Laticrete 255 platinum will also work.
Hate dat cobcrete as
much as auto correct….concrete duh 
I have a slab cobcrete garage floor that has a crack in it. It is probably due to settling. The slab is at least 50 years old. It has always had a hydrostatic water seepage problem.
Could the floor be repaired using a modified thin set to level, fill and span the crack? I would like to build it up 2-3 inches as needed and feather the front edge for drainage. This would also facilitate loading and entry into the garage?
If this is used as a primary floor should additional sealer be applied at some time after curing to increase durability and functionality? Would you advise having expansion joints? Should the process be done in stages?
(Example) 1) Fill cracked area (2) Allow to set and cure fully (3) Skim and feather out over crack filled area (4) Allow to set and fully cure (5) Install and afix expansion joint material [tarboard strips?] Laid out in 3×3 foot squares to floor with mastic. (6) Pour and fill squared areas (7) Skreet level (8) Allow to set and cure fully.
Please advise? Would regular concrete or some type of other mix be better advised than modified Portland cement aka thin set?
Hi Brian,
First of all, Portland cement is NOT also known as thinset. Thinset has portland in it, but it IS NOT a wear surface. If you were planning on installing tile over it then I would suggest deck mud as your substrate, which would isolate the cracking from the tile surface above it. If you are looking for a cement-based finish without a floor covering over it I’m afraid I can’t be much help. But I can tell you the thinset will not work.
I bought a rubber soundproofing underlayment. I plan to glue it with a urethane adhesive (per installation instructions) to a two layered (5/16 OSB on top of 7/16 plywood) substrate and use a 50 lb roller to smooth it and remove all bubbles. I think joists are 16″ on center. Feels pretty solid. Documentation says that I can lay ceramic tile directly on rubber underlayment. My tile is porcelain 6″x24″ and I am skeptical. I am trying to minimize height so I really do not want to add 1/4″ hardi. Have you ever used a rubber soundproofing underlayment? If you think I should not tile directly to the rubber, do you think I could use DITRA on the rubber ?
Thanks,
Sara
Sorry I was wrong about the substrate. The plywood is 1/2″ and the OSB is 5/8″. Total height is 1 and 1/8 inch. I do not feel like I need hardi for stability, but I’d like to hear what an expert thinks.
Thanks,
Sara
Hi Sara,
It depends on which particular membrane you have. If it says you can tile directly to it then yes, you can use ditra over it.
Roger, you rated the unmodified thinsets, how about you rank on the modified.
(2) Would you use Ditra set unmodified over a mud deck or go with the modified thinsets?
Hi John,
Sure, which 100 modified thinset would you like ranked?
There are simply way too many modifieds, all with different properties so it’s difficult to compare them without knowing exactly what you’re looking for. I would use ditra set if you’re using schluter materials, otherwise I would use modified.
Man, this stuff is never easy!! So I have durarock shower walls and a custom mortared shower pan… I plan on applying hydroban on shower floor and hydro barrier on all the walls… I’m also doing Ditra-heat on the bathroom floor. I have 12×24 ceramic tile going on shower walls and bathroom floor and small tile on shower floor. My question is this… modified under the Ditra heat but Unmodified everywhere else? Or should I be doin modified in the shower walls/floor as well??
Up until today I was doing modified everywhere :/
Hi Greg,
Unmodified only between the ditra heat mat and the tile. Modified everywhere else.