Thinset Mortar

Thinset mortar is made from a combination of cement, aggregates and special additives designed for setting all sorts of tile, stone, marble and thin brick pavers over concrete or masonry surfaces. Thinset mortar is usually available in white and gray. It is meant for use on interior horizontal surfaces either above or below grade. In this article, we will give you some useful tips for choosing and applying a thinset mortar around your home.

Preparing Surfaces

When applying thinset and installing your tile, the substrate’s surface must be expertly cleaned. All dirt, grease, mildew, oil, paint and any other foreign contaminants must be removed. A dry method of cleaning, such as blasting with sand or pellets is often preferred. Manual cleaning can be done when on a shoestring budget.

When manually cleaning, a wet method is used. You need to use a degreaser and scrub the surface vigorously Rinse and dry the surface thoroughly before checking for any remaining contaminants.

To check for any oil remaining on the surface, you can sprinkle water over the area to see if it beads or not. If the water beads, then it is not free of oil or grease. When the surface is clean and dry, the water should be quickly absorbed if the surface was cleaned properly.

One concern in particular that needs to be looked out for, when preparing the surface, is the effects of efflorescence. There are two types of efflorescence: primary and secondary. Primary efflorescence occurs when the masonry product is formed. Salt contained in water is left behind when the product dries. The white powdery residue that is left behind is known as primary efflorescence.

Secondary efflorescence on the other hand forms after the product is formed and is well past being cured. The same type of white powdery residue forms when masonry gets exposed to salt. It forms while the salt water soaks into it, whereas primary efflorescence forms when the salt water leaves the masonry. With secondary efflorescence, the salt breaks down the cement and the residue forms during the process. Secondary efflorescence causes the structural integrity of the stone to be compromised, whereas primary efflorescence doesn’t.

Thinset Mortar Choices

It is important to use the proper type of thinset mortar for the type of tile and surface that you are installing it on. Here we will provide some common scenarios and describe the type of mortar to use for each. Firstly, if you are using a darker grout, use a gray colored thinset and if you are using a light colored grout, use a white thinset.

Unless you are an expert and a quick one, you should avoid getting a fast setting thinset mortar to avoid being rushed through the job. There are also sanded and unsanded thinset mortars. You can use a sanded one on floors or countertops and unsanded or sanded on walls, countertops and fixtures. You can always ask the retailer for advice regarding your specific situation.

Ceramic tiles: almost any multi-purpose or polymer modified thinset mortar can be used when setting ceramic tile over a concrete substrate. A high quality latex modified thinset mortar should be used if you are installing ceramic tile over a vinyl floor or wooden substrate.

Fully vitrified porcelain tiles: These need to be installed using a latex modified thinset mortar or a basic thinset mortar mixed with an acrylic latex additive.

Mixing Thinset Mortar

To mix a 50 pound bag of thinset mortar, first add about 5 quarts of water to a clean mixing container. Next add the 50 pounds of mix and stir until it becomes thick and creamy. You may use a power drill fitted with a proper mixing bit.

Once it is the proper thickness and nice and creamy, let it sit for ten minutes. Never add any water to it after this sitting period. It is important to have the amount of water in the mixture correct before you let it sit for 10 minutes.

Remix the mixture before use. You will have half an hour to an hour to use the product once it is prepared, depending on the humidity and temperature. Most brands of thinset mortar vary slightly in the mixing directions, so read the instructions of your product before mixing. The thinset mortar should have a nice consistency that doesn’t allow it to loose its shape when spread. It should be similar to the consistency of peanut butter.

Applying Thinset Mortar

One 50 pound bag of thinset mortar will cover an area of about 75 square feet. First thing you will have to do is select the proper trowel for the job. You should always comply with any specific manufacturer’s directions as well.

What Trowel to Use

Large ceramic tile, quarry or brick paver: Use a trowel with notches that are a quarter inch wide, a quarter inch apart and 3/8 inch deep.
Slate: On slate, use a trowel with notches that are a quarter inch wide, quarter inch apart and a quarter inch deep.
Small ceramic tile: On ceramic tile that is three inches or smaller, use a trowel with notches that are V-Notches and 3/16 inch deep.


1. With steady even pressure, apply a thin even coat with the flat edge of the trowel.

2. Then use the notched edge of the trowel to apply a second coat and form nice even ridges for the tiles to set evenly on. Go ahead and cover a 20 square foot area in this manner.

3. The tiles should be dry when they are installed. Set them so that one fourth of their thickness sinks into the thinset mortar. Lay them in place with a slight twisting or turning motion.

4. Make sure it is square and make any adjustments immediately after laying the tile.

5. Wipe the excess mortar from the tile’s surface with a wet sponge.

6. Allow the tiles to cure for about 72 hours before grouting.

That’s about all there is to using thinset mortar. As mentioned earlier, all brands differ slightly, so be sure to read the manufacturer’s directions before using.

Tips and Tricks

The above mentioned method is one way of laying tile. Another way to do it, is to spread the thinset in a similar fashion, but on the backs of each individual tile when laying them instead of applying the thinset to the substrate. You should consult with the tile dealer to find the best way to do it for the type of tile you are purchasing and the surface you are laying them on.

If you apply the thinset mortar to the substrate and it forms a film or skin before you are done, remove that part of the thinset mortar and reapply it. There are special solutions, such as Mix-21, that need to be used in place of water when installing thinset mortar over a plywood surface. Make sure the temperature has been over fifty degrees Fahrenheit for at least 48 hours before setting your tiles.

When you are done, make sure to clean all tools and equipment immediately with water before the mortar has a chance to set. Now you have a good idea of how to use thinset and you can always get more information from the manufacturer’s that you buy your products from or the retailers.