How to Prevent Cracking in a Stamped Concrete Patio
Efficient, well-planned construction and finishing of your stamped concrete patio is the best way to prevent cracking due to weather or subsoil instability. Follow these guidelines when building your patio to prevent unsightly, dangerous cracks in the concrete.
Step 1: Measure and Dig the Patio Foundation with a Drainage Slope
Measure and mark the entire perimeter of your stamped concrete patio with string and stakes. Advise the local utilities that you are planning to dig for a patio so they can send a consultant to help you find underground pipes and cables. Dig down 8 inches into the soil, removing all rocks, tree roots and other obstructions. Lay the patio out with a slight drainage slope of 1/4 inch for each 4 feet of length and width away from the house. This will prevent precipitation from running off into your foundation.
Step 2: Compress the Subsoil Thoroughly
Compress the subsoil under the patio thoroughly with the compactor. Add the sand and concrete to a depth of 4 inches, and compress it, while maintaining the drainage slope.
Step 3: Set Up the Forms to Hold the Concrete
Pound the string stakes down so that just 4 inches shows above the surface. Lay the 2x4 planks into the ground and nail them to the stakes with 2-headed nails, for easy removal of the forms later.
Step 4: Use the Lowest Amount of Water to Cement to Form the Concrete
You can do this step yourself if your patio is only about 100 square feet, but hire a contractor with a cement mixer if your space is 250 square feet or more, to ensure the concrete remains at usable texture throughout the pour. A ratio of 45% water to cement will make a hard and stable patio surface, and will result in a pressure strength of 4500 psi (pounds per square inch).
Step 5: Add Joints for Expansion and Contraction
Joints are thin shallow grooves that allow the concrete to expand and contract with temperature or pressure changes. Use 2 kinds of joints in your stamped concrete patio: isolation joints around the perimeter, to separate the slab from the soil, and contraction or control joints, which allow the concrete to expand and contract in thaws and freezes. Make the contraction joints every 10 feet with a grooving tool soon after the concrete is poured. Add the isolation joints with the groover or with a masonry saw after you take out the concrete forms.
Step 6: Ensure the Concrete Cures Completely
The best way to ensure the concrete cures completely and will resist cracking is to keep it damp for 5 to 7 days after pouring. Dampen the slab well with the garden hose, and place damp canvas covers over it, held down with stones or bricks. Do not use clear plastic covers over colored, stamped concrete, as the color will be ruined.