How to Lay Slate Stone in Wet Concrete

Prepare the foundation for the surface. Mark the edges with landscaping paint and unearth 9 inches with a shovel until the bottom of the expanse is even. Tamp the remaining loose soil with a tamper to stabilize the subsoil.

Fill the site with 3/4 inch crushed rock and tamp it down. Continue adding and tamping the rocks until the base is 3 inches thick.

Set 2-by-4 inch boards on their sides against the inner walls and nail them together to build a form for the concrete. The top side will mark where the surface of the concrete will be.

Mix concrete with a bag of ready-mix. Pour in the manufacturer's suggested amount of water from a hose. Stir until it is pourable, but thick.

Pour the mix over the site. Spread it into corners evenly with a gauge rake. Use a notched trowel to level out the surface. The grooves made by the trowel help the slate adhere. Wait for water to bleed to the top, and then reabsorb about 15 minutes after the concrete is poured.

Set the slate stone on the concrete beginning on one end and working across. Place rubber spacers between pieces for consistent joint lines, and place the stones in a grid, or stagger the joints for a diagonal pattern. Set a bubble level across adjacent tiles and tap higher stones with a mallet until they are level. Make each stone level before moving onto the next. Wipe off any wet concrete from the slate with a moist cloth. Let the concrete dry for four days.

Take the spacers out from between slate stones. Mix grout with equal parts sand and cement, then stir in water until it feels stiff. Press it into joint lines with a grout float. Scrape off excess and wipe it from the surface of the stones with a moist cloth.