How to Lay Slate Tile in Forms

Snap two chalk lines over the center of the surface, one going lengthwise and one across the width. The point where the lines intersect is the center and the starting point for laying the tiles.

Dry-lay the tiles over the concrete slab once it is dry. Arrange the tiles in the pattern you intend to set them in, leaving room for 1/2-inch spaces between each tile.

Mark each tile on the back with a piece of chalk. Make a diagram of the site and plot where each tile will go.

Mix a bag or mortar mix with enough water to make a thick, but spreadable consistency. Spread 1/2-inch of mortar over the center point of the concrete with a notched trowel. Only spread enough mortar to lay four tiles at a time.

Set the center tiles in the mortar according to the intended design. Space the tiles 1/2-inch apart and place a bubble level over each section to ensure each tile is level with adjacent tiles before moving on to the next section.

Continue setting slate tiles from the center to the outer perimeter of the concrete. Once you reach the ends of each row, position the tiles so they are flush against the form if you intend to remove the forms once the mortar and grout dry. If you intend to leave the form for aesthetics, leave 1/2-inch of space between each tile and the form to adhere it to the form.

Make a batch of unsanded grout once the mortar has set for a day. Empty the package into a wheelbarrow and add water, stirring until it is thick like toothpaste. The unsanded grout will prevent scratch marks on the slate tiles.

Press grout between the 1/2-inch spaces with a grout float. Remove spatters from the tiles with a damp sponge. Smooth the joint lines after completing small sections, checking that the grout is level with the forms so rainwater cannot build up around the edges. Give the grout two days to set before mopping the surface with warm water.