Modified Thinset – A Brief History

by Roger

Laticrete 3701What 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. :D 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.

 

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Liza

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

Reply

Roger

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. :D

Reply

Les

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.

Reply

Roger

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.

Reply

Kevin

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

Reply

Roger

Hi Kevin,

You need to use epoxy. Laticrete 255 platinum will also work.

Reply

Brian West

Hate dat cobcrete as :evilb: much as auto correct….concrete duh :bonk:

Reply

Brian West

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?

Reply

Roger

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.

Reply

Sara McGahey

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

Reply

Sara McGahey

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

Reply

Roger

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.

Reply

john

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?

Reply

Roger

Hi John,

Sure, which 100 modified thinset would you like ranked? :D 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.

Reply

Greg

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 :/

Reply

Roger

Hi Greg,

Unmodified only between the ditra heat mat and the tile. Modified everywhere else.

Reply

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