How to Fill a Crack Between Concrete Backers

When installing tile, it's important to have a flat surface on which to work. If the concrete backer board has broken, or if there is a seam between two adjoining backer boards, it's a good idea to patch the seam or the break before laying the thinset mortar and tiles in place. This will prevent cracks in the grout between the tiles, and also ensure that the tiles lay smoothly and evenly.

Trowel
Thinset mortar
Water
Mixing container

Instructions

- 1
  Mix the thinset mortar with water in a mixing container until it has reached the consistency of peanut butter.
- 2
  Scrape the surface of the mortar to create a bead of mortar along the length of the trowel's blade that is approximately 1/8 of an inch in diameter.
- 3
  Press the bead of mortar into the crack or seam with the bead's length running parallel to the crack or seam. This will form a strong backing for the upper coat of mortar, and will help prevent air bubbles from becoming trapped in the crack.
- 4
  Scoop more mortar onto the trowel this time, and apply it to the crack over the top of the bead you applied previously.
- 5
  Scrape the excess mortar off the concrete board using the edge of the trowel.

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