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 that 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.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.