Floor Tile Mortar – ‘Keyboard’ and Mortar Spreading

With a tablespoon of freshly placed mixed floor tile mortar on the subfloor, the next step is to spread it deep enough to lay floor tiles and then “insert” the mix so that it bonds properly with the floor. Using the flat edge of your notched trowel, gently spread the mortar to a size large enough to set the first floor tile in place.

When doing this, be very careful not to cover your chalk line or any other important alignment guides you may have previously done on your floor, which were necessary for dry-lay projection and sight line direction. It’s not a big deal if it doesn’t exactly hit the chalk line, as it’s better not to hit it. The moment you press the tile into the mortar bed, this will actually squeeze the mortar out to cover a larger area, so it’s best to have it hang on the lines a bit when you spread.

In this sense of initially keying in the mortar, you don’t just want to spread it like you’re buttering toast, but more like the way a child would butter a slice of toast. To explain this, I mean not methodically spreading the mortar in one direction, say right to left, for example, but following a more irregular pattern spreading it from several alternating angles. This allows the tile mortar to adhere much better to the floor by keeping the spread angles erratic, yet smooth enough not to go over the marks.

Once you’re happy with the insertion process, which should take about 30-60 seconds per floor tile, you’ll also want to make sure the mortar bed is about 1/2″ to 3/4″ deep. inch deep. The next step after this is to place the ‘grooves’ into the mortar bed with the serrated edge of the trowel. When done correctly, this should basically turn your mortar bed into something very similar to a freshly plowed field.

To do this correctly, always pull the paddle toward you and don’t push it. Not only is it easier on the back, but it also allows you more control of your lines, so the first step is to get into a comfortable position. Next, place the notched edge of your trowel on the edge of your spread mortar, tilt it at about a 45-degree angle with the flat edge facing you, press down hard on the floor, then pull back straight. always keeping the pressure down.

You should hear a steady scraping sound when done correctly, and when you get to the end of your scraping, lift the paddle slightly, turn it about 90 degrees, and then slide it down. This will create a small mound of excess mortar at the end of your ‘plow field’, troweling it clean and ready to use for the next floor tile to be laid in a new bed.

That’s basically all it takes to type and spread your mortar, and once you get the hang of it, you’ll soon find that it follows a simple, rhythmic pattern. However, one last important point is to always keep the ‘grooves’ in a straight line. Never try wavy lines and fancy curves, as the mortar will not spread properly once the floor tile is pressed on top, and can cause unwanted trapped air bubbles under the floor tile when it dries. If there is no solid support under a point in a floor tile, such as an air pocket, then you could be looking at a potentially cracked tile waiting to happen over time.