I am often asked what type of thinset should be used modified or unmodified? So to answer this question you first need to know what kind of tile is being installed and on what kind of surface. Let"s understand how thinset works and how it bonds to the tile and to the substrate it is being applied to. Thinset is basically a mixture of sand, and cement and other compounds to facilitate the hydration process. Thinset is the “Glue” that bonds the tile to the surface to which it is applied, and it does this by growing crystals as it dries and cures. The crystals interlock and penetrate into the surface of the tile and the substrate, bonding it all together. The longer the thinset is able to grow crystals the strong the bond and the strength of the thinset. So what kind of thinset should be used in any given application? Well there is unmodified thinset, and modified thinset, and other kinds of thinsets, but we are just going to deal with these two types which are the most widely used. Unmodified thinset is a thinset that has no polymers added to it, a modified thinset is a thinset that has either polymers added to the powder during manufacturing, or an unmodified thinset that is mixed with a liquid polymer on the job site just before it is to be used. Modified thinset is the most widely used mortar these days and is recommended for most applications and types of tile. So why is there polymer in the thinset anyway? Well it is there to help the thinset retain moisture so it can grow those crystals we talked about earlier. Many of the substrates that tile is installed on are very porous and thirsty and will absorb the moisture present in the thinset, which in turn will prevent the thinset from gaining strength, the polymers help with this problem by keeping the moisture in the thinset so it can Hydrate (grow crystals) properly. So when you go to the store you will see that not all thinsets cost the same, some are more expensive than the others, well you get what you pay for, the cheaper thinsets have less of the needed components, and the more expensive ones have more, so by extension better. Modified thinsets also add an adhesive quality to the bonding mechanism, as well as flexibility, enhancing the strength of the tile assembly. So modified thinset is used to install porcelain tiles on all kinds of substrates that call for a modified thinset, but we are not going into that here, because I am just trying to explain how thinset works, not specific applications, except for one.Now unmodified thinset was becoming a seldom used product until Schluter came along and required it for installing tile to Kerdi and Ditra. Now unmodified thinset, as the name suggest, has no polymers. So what is the difference and why should it be used on Schluter products? Here is the thing, the polymers in a modified thinset help it retain moisture, but if the tile does not absorb any moisture, and the substrate is also impervious, then the moisture in the thinset becomes trapped, because of the polymers it need to evaporate for the thinset to dry completely, extending the drying time greatly. The only place for the water in the thinset to escape is the grout lines at the edges of the tiles. So this is where unmodified thinset has an advantage, trapped moisture in this case becomes a benefit. In unmodified thinset moisture that is not consumed by the hydration process will not impede the hardening of the thinset and will eventually escape. The damp cure that the impervious sandwich creates only makes the thinset stronger and promotes a very tenacious bond to the tile. So that’s how thinset works and I hope this gave a bit of help to decide whether you need an unmodified or modified thinset for your install. All tile installed by Sal DiBlasi, Elite-tile Company, in the Boston North Shore area. This video contains affiliate links, which means I will receive a small commission if you click on the product link.
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