How to Repair Slab Paving
Concrete paving slabs are a common choice of paving for patios. The same slabs can also be used for paths, but for drives, stronger and thicker, hydraulically-pressed slabs must be laid on a much stronger base. Normally, paving slabs are set on dabs of mortar on a sand base, but they may also be laid on a solid bed of mortar, a method that is always used when laying heavy-duty slabs for a drive.
Repairing slab paving
A slab may have broken because something too heavy has been placed on it or as a result of something hitting it. Sometimes, individual slabs may become loose or may sink, in which case they will need to be lifted and re-laid.
If the joints around the slab have been filled with mortar, the first job will be to chip this out, using a narrow-bladed masonry chisel.
If possible, remove a broken slab from the centre, working outward; you can use a bolster chisel or a garden spade to lever up sections or whole slabs, but protect the edges of adjoining slabs with pieces of timber. Clean out the bottom of the hole, removing all old mortar, and level it using builder’s sand tamped down with a stout piece of wood – allow about 10mm for the mortar. Mix up a batch of mortar using dry ready-mix and put down five dabs, one in the centre and one near each corner. Also lay a fillet of mortar along each edge.
Lower the new slab, or the old slab if it is undamaged, into position and tap it down with the handle of a club hammer. Check that the slab is level with its neighbours by placing a spirit level across them. Adjust as needed, then when perfectly level fill the joints with more mortar.
This form of paving employs pieces of real stone or broken slabs (whole slabs of real stone are prohibitively expensive) and is popular for paths, although larger areas may also be paved in this manner. It can be laid in one of two ways: on a bed of sand or a bed of concrete. Like full-size paving slabs, individual pieces may break, sink or work loose.
When repairing crazy paving, you may need to re-lay quite large areas. As when laying new crazy paving, work from the sides toward the centre, using the biggest pieces with the straightest edges along the sides, then filling in with smaller pieces.
Whichever way you lay crazy paving, the joints should always be well mortared, and the mortar finished flush or shaped with a pointing trowel to give V-shaped grooves around the slab.