Instead of tearing out concrete and replacing it with slate, update it with a painted faux-slate finish. Clean the concrete thoroughly to ensure the paint sticks; then use a latex patio enamel to create the base or background color. Add color variations with paint brushes and sea sponges to mimic your favorite shade of slate.
Concrete -- especially on an exterior surface -- requires a thorough cleaning before you paint it; otherwise, the faux slate finish may not turn out as expected. Sweep or brush off the concrete; then scrub it with a degreasing and etching liquid designed for concrete to remove all types of stains. A stiff scrub brush works well for a small area, or use a push broom for a large surface such as a patio. Rinse off the concrete with clean water; then allow it to dry for at least 24 hours or until you are certain it is completely dry. It may take longer to dry in humid weather.
Applying the Base Color
The concrete needs a base coat of concrete paint before the faux-finishing fun begins. Pick your favorite basic slate color such as a dark or medium gray. This color will show through in some areas after you create the faux-slate finish. Use a water-based enamel paint specifically designed for concrete patios or floors to ensure the paint adheres properly. Brush on the paint if painting a relatively small area, or use a roller to apply the base coat to a large concrete surface. Allow the paint to dry for at least 24 hours or as recommended on the paint container before touching the paint or applying the faux finish.
Creating the Faux-Slate Finish
Cover an area near the concrete with a folded plastic tablecloth or sheets of newspaper.
Pour each of the acrylic paint colors into small pools in a shallow tray, or in separate trays, if you prefer that the paints do not mix. Set the trays atop the tablecloth or newspaper.
Dip the edge of a sea sponge into one of the slate paint colors. Dip a nearby portion of the sponge into a second paint color.
Dab the sponge over portions of the base-coated concrete to create wide bands of color. Dab only once per area for a subtle effect, or dab repeatedly to make the new color more obvious against the base shade.
Dab or brush the wet paint gently with a rag or paintbrush to soften the color variations, if desired.
Continue dipping the sponge into one or more paint colors at a time, dabbing it over areas of the concrete until the desired slate look is achieved.