Tool Tech: the easy way to replace

Best techniques to get the job right with Tim Rumball How to use tools

Replacing broken patio slabs

Cracked slabs spoil garden patios and paths. Tim Rumball shows how to replace them

IT 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.

Replacing broken slabs is quite straightforward but can be heavy work. Lift slabs and bags of cement or sand with care

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.

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

Kit needed for patio-slab replacement

1. Shar 2. l b hammer 3 Cement powder

9. Garden spade

. New slabs

8. Plugging chisel/ screwdriver . Spirit level

7. Plank and block of wood 6. Bro m handle

Explanation of terms

Sharp sand: A coarse and strong general-purpose sand used for fine concrete work. Mortar: A mix of sand and cement powder that dries to a stone-like consistency. Plugging chisel: Steel chisel with a long, thin blade, the

head cut at an angle. It’s used for chipping out mortar. Club hammer: Hammer with heavy, block-shaped head. Spirit level: Tool with long, straight sides and inset bubble-tube for determining horizontal and vertical surfaces.

Step by step

Replacing a broken path or patio slab

1Rake out old grout around the edges, place a plank of wood along one edge and use the edge of a spade or a strong screwdriver to lever up the patio slab.

2Remove the old slab, break up and remove old mortar then add sand and firm down level until surface is about 1∕2in (1cm) below the base of surrounding slabs.

Do’s and don’ts of patio slab replacement

Do ✓ Mix mortar using fresh cement powder and sharp (coarse) sand in the ratio of four scoops of sand to one of cement –mix it well and add a little water if it’s very dry. ✓ Clean up the facing edges of slabs alongside the one you’re replacing, removing old grout, mortar and dirt before dropping the new slab in.

DonÕt ✗ Tamp down the new slab until you’ve checked that all joints are equal in width and the slab aligns with the ones either side. Tap the edge with a mallet and block to move the slab. ✗ Compromise on level –keep adding or removing sand until you get the slab as level with surrounding slabs as you can. Uneven slabs show, and are a trip hazard. Clean facing edges of slabs alongside those being replaced

Mix mortar with fresh cement powder and sharp sand

3Dot five fist-sized dollops of 4:1 sand/cement mix into the hole, one in the centre and one in each corner, then carefully lower the slab into the hole.