How to use tools Best techniques to get the job right with Tim Rumball Replacing broken patio slabs
Cracked slabs spoil garden patios and paths. Tim Rumball shows how to replace them
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T takes a bit of effort to replace broken slabs in paths or patios, but it’s a lot cheaper than having it all re-laid and it can transform a shabby outdoor space. This is best done when no frost is forecast for a few days. If sub-zero temperatures threaten, leave doing it until the weather warms up. Measure and count the number of broken slabs, and buy replacements of exactly the same size, finish and colour. If this is not possible, and the broken slab is in a prominent position, consider lifting an unbroken old one from an unobtrusive position on the patio/path and use it to replace the broken one. Put the new slab in the unobtrusive position. Tools needed As well as the slabs you’ll need sharp sand, cement powder, a mortar mixing tray, a plugging chisel or an old screwdriver to rake out the old grout, a large spirit level, a club hammer or mallet, a garden spade to lever up old slabs, a short piece of old plank and a block of wood. An old broom handle is also useful to roll the old slabs out of their holes (which saves your back). Preparation Clear the space around the slabs you’re working on, and sweep up the debris. Rake or chip out the grout in joints around the edge of the slab with a plugging chisel – I find an old slot-head screwdriver works fine if the joints are filled with sand rather than mortar. Place a short plank of wood along the edge of a slab next to the one you’re lifting, and lever up the slab using the blade of the spade. Slide the broom handle under the slab, ends resting on slabs either side, lower the lifted slab onto the broom handle and roll the slab out of its hole.
Replacing broken slabs is quite straightforward but can be heavy work. Lift slabs and bags of cement or sand with care
Dealing with mortar/cement Break up the old mortar in the slab hole and rake it out if it was laid on a cement/ sand mortar mix. Some are just laid on sand but these are much more likely to sink or crack over time, so lay your new slab on mortar. Also, carefully chisel off any mortar sticking to the edges of surrounding patio slabs, and brush or scrape off soil. Mix your mortar, four shovels of sand to one of cement, on a plastic tray – it can stain if you mix it directly on paving. Use fresh cement powder as it goes off when exposed to moisture and air. Mix it thoroughly, and if it’s very dry add a little water. Add sand to the slab hole and firm down until it’s roughly level and 1/2in (1cm) below the base of surrounding slabs. Drop five generous fist-sized dollops of mortar in the hole, one in the centre and one each at the four corners. Placing slab Carefully lower the replacement slab into position checking that it is in line
with surrounding slabs – the grouting space on all four sides should look even. Tamp it down gently and evenly, tapping the slab of wood with the club hammer, until the new slab is level with all four surrounding slabs. Work methodically over the whole surface, check alignment regularly with the spirit level, and don’t tap too hard otherwise you’ll break the slab. If it won’t settle deep enough, lift the slab, remove a little mortar and try again. If it settles too deep lift the slab, add a little mortar and try again. It’s a fiddle, but worth the effort to get it right. When the new slab is level with all surrounding slabs, pack joints around the edges with sharp sand or a dry mix of 4:1 sand and cement powder. Sweep up thoroughly. If you want an even finish, use a patiocleaning product then pressure-wash the old slabs to even up the colour. Even if you don’t do this the new slabs will begin to blend in with surrounding old slabs within a few weeks.
A screwdriver can be used to rake the old grout from between slabs unless it has been mortared, in which case you’ll need a plugging chisel and hammer Break up old mortar and rake it out. Also remove soil and other organic matter that can affect the stability of the slab 52 AMATEUR GARDENING 8 FEBRUARY 2020
Once the slab is square and level, trickle dry sand into the joints and pack it in firmly
