With a scoop of mixed floor tile mortar laid out fresh on your subfloor, the next stage is to spread it out to a sufficient depth for laying floor tiles, and then ‘keying-in’ the mix in order for it to bond correctly with the floor. Using the flat edge of your notched trowel gently spread the mortar out to a size large enough to bed your first floor tile into place.
When doing this, be very careful not to cover your chalk line or any other important alignment guides you have made on your floor prior, which were necessary for dry laying projection and line of sight direction. It’s no big deal if you do not exactly meet up with your chalk line, as it is better to fall short of it. By the time you press down the tile over the mortar bed, this will actually squeeze out the mortar to cover a larger area, so best to hang back a little from your lines when spreading.
In this sense of initially keying-in the mortar, you want to not just spread it as though you were buttering a slice of toast, but more like the way a child would butter a slice of toast. To explain this, I would mean not to methodically spread the mortar in one direction only, from say right to left for example, but follow a more irregular pattern by spreading from various alternate angles. This allows the floor tile mortar to bond much better with the floor by keeping the spreading angles erratic, but still gentle enough so that you don’t overstep any marks.
Once you’re happy with the keying-in process which should last for around 30 to 60 seconds per floor tile, you want to also make sure that the keyed-in mortar bed is at an approximate depth of between 1/2″ to 3/4″ inch deep. The next stage after this is to then set your ‘furrows’ into the mortar bed using the notched edge of your trowel. When done correctly, this should basically turn your mortar bed into something very similar to a freshly ploughed field.
To do this properly, always pull the trowel towards you and not push away. It’s not only easier on your 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 to the edge of your spread mortar, tilt it to an angle of about 45 degrees with the flat edge facing towards you, push down hard on the floor, and then pull back in a straight line, always maintaining downward pressure.
You should hear a constant scraping sound when done correctly, and when you come to the end of your scrape, lift the trowel slightly, flip it about 90 degrees, then slide it downwards. This will create a small mound of excess mortar to the end of your ‘ploughed field’, by wiping it from the trowel and making it ready for use for the next floor tile to be laid in a fresh bed.
Basically, that’s all there is to keying-in and spreading your mortar, and once you get the hang of it you will soon find that it follows a simple and rhythmic pattern. One final important point though, is to always keep your ‘furrows’ in straight lines. Don’t ever attempt wavy lines and fancy curves, as the mortar will not spread out properly once your floor tile is placed on top with pressure, and can result in unwanted trapped air bubbles underneath the floor tile when dry. If there is no solid support under a point in a floor tile such as a pocket of air, then you could be looking at a potentially cracked tile just waiting to happen given time.
Source by Matthew Seiling
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