How to Install Deck Slate on Pressure-Treated Plywood

Lay out your deck. Choose one edge of the deck and measure across to determine the center point, then make two marks at opposite ends of the deck at the center. Snap a line from point to point across the deck. Determine the center for the opposite direction, and mark the center across the chalk line. Use the framing square to draw a square line perpendicular to the chalk line on your center mark, then snap the other mark so you have two lines intersecting the center of the deck.

Lay two pieces of slate tile in a row, with at least 1/4 inch between them. Measure the distance between the two tiles. Transfer that measurement to your deck. Measure out that distance from your chalk lines and make marks at opposite ends of the deck, then snap an additional line between those two points. Continue this process until you have a series of 2-by-2 grids on the deck.

Mix your thinset according to the manufacturer's instructions. Use a drill to mix the mortar, and let it sit for several minutes after you initially mix it so that the thinset can slake and the water soak completely into the polymers and additives. Mix it one additional time before using it to install your deck tiles.

Pick a section of the deck as your starting point, and work your way back from there. Spread an even layer of thinset onto the pressure-treated plywood within a grid using the notched side of the trowel. You can cover the lines, but leave enough showing so that you can use them as a reference point at the corners. Work grid by grid, and never spread more than two grids at a time.

Press a piece of tile firmly into the bed of thinset and move it around slightly in all directions before aligning it with the chalk lines. Repeat this process for each piece, and use the lines as a reference point to keep the installation square and straight. You cannot use spacers with slate tiles, as they are not uniform in size; so follow the lines.

Mark any necessary cuts with a grease pencil and cut them on the tile wet saw. Be sure to dry off the back of each piece completely before installing it into the bed of thinset, because the water will ruin the bond between the mortar and the tile. Allow a minimum of 24 hours before grouting the installation.