You’re in your local big box home improvement store staring at two types of mortar: modified thinset and unmodified thinset. Nothing has prepared you for this moment. What the heck is modified thinset? And how is it different from unmodified thinset? Which one should you choose?
If you’ve found yourself pondering this and other life choices in the middle of the building materials department, this guide’s for you. Here’s your introduction to thinset.
What is Unmodified Thinset?
Both types of thinset are used as a tile adhesive for floor application. Thinset is added in a thin layer to a floor (typically a cement or concrete floor) in a 3/16 to 1/4 inch layer. Then the tile is installed on top of this thinset layer.
You may know thinset by its other common terms, such as mortar or mud.
Unmodified thinset is a blend of portland cement that’s mixed with sand (silica), and water retention additives, usually lime. Water is then added to the blend to create the final mortar.
Unmodified thinset is also known as dry set mortar.
This type of thinset mortar is best for ceramic or natural stone installations. It works well over many different types of surfaces and can be applied up to 1/4 of an inch thick.
Unmodified thinset is assigned the number A118.1 by the American National Standards Institute, or ANSI for short. When shopping for your thinset mortar, look for this number on its bag.
Not all unmodified thinsets are equal. In general, the more cement (as opposed to sand) in the mix, the better the quality of the thinset. This is because high cement content leads to a sturdier mortar.
Different manufacturers create unique blends and ratios using the same ingredients. However, you can’t necessarily add more sand or cement to improve the quality of a low grade product. Thinset mixes are specifically blended with exact ratios to create the desired outcome.
What is Modified Thinset?
Modified thinset contains the same ingredients as unmodified thinset but also includes an additional binding substance, or polymer. Polymers, such as latex, may either be added by the user or the manufacturer. These polymers not only improve binding but they also improve strength and durability.
This polymer may come in powder form and be added to the dry mix by the manufacturer. The dry mix is then activated with water by the user.
The polymer can also come as a liquid additive. Instead of using water, the user mixes the liquid polymer into the unmodified thinset powder
Modified thinset is also known as latex or polymer modified mortar.
According to the ANSI, modified thinset must meet the same criteria as unmodified thinset. This also means that modified thinset has more than one ANSI assigned number on its bag. If your bag contains the number A118.1 and any additional number, it’s modified. That’s because A118.1 indicates any and all types of thinset.
A Brief History of Thinset
Of the two, unmodified thinset has been around the longest.
Standard tile installation required a full bed method. This was a thick, two- to three- inch application of portland cement and sand before setting the tile in place.
Why was the tile bed so thick? That level of thickness was necessary to allow the cement to cure. Otherwise, the cement would not retain enough moisture.
When portland cement cures, it goes through a chemical process known as hydration. During hydration, the cement reacts to the water in the mix and forms crystals that interlock with each other. This is what either strengthens or weakens the cement. The ratio of water to cement will determine the strength of the mortar.
This is because the interlocking crystals within the cement will continue growing as they’re exposed to water. However, once these crystals are no longer exposed to moisture, they stop growing.
You want the crystals to grow for as long as possible. The longer amount of time the crystals grow, the more they have an opportunity to interlock and strengthen the mortar.
This is why when curing, it’s important that the moisture level within the cement remains high. It will ensure that the thinset continues to strengthen at a gradual but deliberate pace.
Modified thinset was developed to aid in moisture retention. In the 1940s, chemical engineer Henry M. Rothberg introduced a synthetic liquid latex polymer that was later marketed as Laticrete. This polymer helped to strengthen cement while also making it more flexible.
Then in the 1960s, the Tile Council of America improved upon Rothberg’s creation and came out with a modified thinset that contained dry polymers. These polymers were activated when the user added water. This modified thinset product was even easier to use and became a instant hit
Why Use Thinset at All?
Can you get away with applying your finish floor directly over your concrete or cement subfloor (with the help of an alternative adhesive)? Probably. Thinset isn’t the only solution available. Plus, thinset can introduce a lot of challenges to your home removal, especially if you’re a weekend warrior who doesn’t work with the medium often.
Among the drawbacks of using thinset are:
- It’s difficult to find the perfect consistency. Sometimes even the humidity and direct sunlight can make it difficult to mix your thinset mortar to the right thickness.
- You have to mix your bags. There’s no other way around it. Thinset doesn’t come pre-mixed, so you’ll need to mix powder with a liquid (typically water) to activate.
- Thinset turns hard. You have to work reasonably quick with thinset.
- You can’t mix it in big batches. Because thinset can turn hard quickly, you’ll need to work in small batches, which can be laborious.
However, working with thinset does provide quite a few benefits, too.
- One major benefit is that thinset won’t react to water once cured. You won’t have to worry about this product expanding or contracting over time.
- Another benefit is mold resistance. Unlike other materials, this concrete inhibits the growth of mold.
- Finally, thinset is pretty easy to apply to a subfloor. If you can schmear a bagel, you can apply thinset to your floors.
Which is Better: Modified or Unmodified Thinset?
So, which type of thinset should you choose for your home renovation?
In the flooring industry, there’s a huge debate over which type of thinset is best.
Because certain types of modified thinset mixes don’t even require water, modified thinset has gained the reputation of being easier to work with. Modified thinset is also considered stronger than unmodified thinset. But does this mean that modified thinset is better for all applications? Not necessarily. Both types of thinset have benefits and drawbacks.Modified thinset is also considered stronger than unmodified thinset. But does this mean that modified thinset is better for all applications? Click To Tweet
Choose your thinset based on the type of tile you’re applying and also the type of subfloor that you’re applying it to. Some flooring manufacturers recommend that you go with a specific thinset during installation. Be sure to follow these recommendations when installing your own floors.