Now you have calculated the exact size of your patio and the fall you can begin marking out the area and making plans for excavation. We recommend marking the perimeter of the patio using pegs and a builder’s line or string. The area you will be marking should be around 5-10cm wider than your planned patio. This is because you are actually marking the area of the sub base and not the patio itself. The sub base will need to be a little bigger than the patio to give it a sturdy foundation. If you are laying your patio next to your house, start where the patio will meet the wall. Measure the length of your patio outwards from your first peg and knock your second peg into the ground. Mark the length using string tied to each peg and continue until all four corners are established. If your patio will not be against a wall start with any corner and mark using the same method.
Now you will need to calculate the total depth of all materials which will be used to comprise the patio’s foundation. The foundation will consist of a compacted sub base, a sand screed (or thin blinding layer if using mortar), mortar (if using) and the
concrete slabs themselves. The sub base for a standard domestic patio will typically be no less than 80mm in depth, however aiming for the 100mm mark will ensure a strong sub base. A layer of mortar will be around 50mm. The total depth of all these materials combined will be the height of the foundation at its highest point, and how deep you will need to excavate for your patio to be level with the ground around it
