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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Greg

Hi Roger,
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?
Thanks again
Greg

Reply

Roger

Hey Greg,

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.

Reply

Matt

Hi Roger,

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.

Reply

Roger

Hey Matt,

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!

Reply

Matt

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?

Reply

Roger

Hi Matt,

Yes to both with the TEC.

Reply

gary

Roger,

I can’t find laticrete my tile store recommended prospec permaflex 600
will that work?

Reply

Roger

Hi Gary,

Yes, good stuff.

Reply

gary

Hey Roger,

:oops: 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… :bonk: What kind of problems, if any, am I looking for with this stuff or is it a RDWHAHB?

Reply

Roger

Hey Gary,

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.

Reply

gary

Hi Roger,

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.

Reply

Roger

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.

Reply

Ross

Hey Roger,

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?

Reply

Roger

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.

Reply

terry

Hi Roger
Can I used hydro ban over duroc .then set porcelain tile with modified thin set ?

Reply

Roger

Hi terry,

Yes you can.

Reply

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