Almost everyone who has installed or helped to install porcelain or glass mosaic tile has had to correct the age-old problem known as thin-set mortar squeeze-up between each tile. The removal of the mortar is probably the least favorite part of a tile installation and many times reserved for the newest member of the team who has to rake out the excess mortar with a tile spacer, margin trowel, a piece of cardboard, or even a popsicle stick.
To eliminate this problem, many installers use some reasonable logic to solve this dilemma. You would think if squeeze-up is to be eliminated, the use of a smaller trowel would be the best choice. Many times, this trowel of choice is a 5/32” or 3/16” “Vee” notch, but actually, this is a really poor decision. The Vee-notched trowel provides about 8-12% mortar coverage on the back of the tile, but many times these mosaics are installed in wet areas which require a minimum mortar coverage of 95%.
If a suggested alternative would be a ¼” x ¼” x ¼” or possibly, depending on the thickness of the mosaic, a ¼” x 3/8” x ¼” trowel, most people would say, no way. However, both of these trowels will provide full mortar coverage, NO squeeze-up, and the technique is really simple.
Start by cleaning and dampening the floor or wall substrate, key in the mortar with the flat side of the trowel, followed by notching the mortar in one direction in a straight line. Prime the flat side of the trowel with a small amount of mortar and pull it across the trowel ridges, effectively knocking the ridge down into the valley, which provides a smooth, consistent coating of mortar as seen in the photo. Place the mosaic tile into the thin set mortar at the desired location and beat in with a beating block and mallet or grout float.
As heard many times while demonstrating this technique, attendees say, “It can’t be that easy!” It is that easy and it works every time. Try it on your next job and save yourself a lot of time and frustration. Do it right the first time.