How to repoint paving slabs

From Marshalls. This guide draws on the video "How to professionally point a patio quickly" from Marshalls, one of the UK's leading manufacturers of paving and landscaping products. The method they demonstrate uses a brush-in jointing compound and applies to most standard patio joints.

1. Assess the joints before you start

Walk around the patio and look at the condition of the pointing. Crumbling, loose, or hollow-sounding mortar all need clearing out. Use a pointing key or a cold chisel to test the joints. If the mortar sounds hollow when you tap it, it has lost its bond and needs to come out even if it looks intact on the surface.

While you are at it, check the slabs themselves. If any are rocking, sinking, or cracked, sort those out first before repointing. Pointing over a moving slab will only crack the fresh joints again within months.

2. Clear out the old pointing

Use a plugging chisel and lump hammer to rake out all the old mortar to a depth of at least 15 to 20 millimetres. Work along each joint and get out as much loose material as you can. A reciprocating tool with a mortar-raking blade speeds this up considerably on larger patios.

Once you have raked out the joints, brush away all the debris with a stiff brush and then blow or vacuum out any remaining dust. The cleaner the joint, the better the new material will bond. Do not try to apply jointing compound over even a small amount of old crumbling mortar.

3. Choose your jointing material

You have a few options, each with trade-offs. Traditional mortar (sharp sand and cement at around 4:1) is cheap and familiar, but it needs mixing properly, has to be kept damp while curing, and can stain the surface if you are not careful. It is a good choice on older or irregular joints where you need to pack material in firmly.

Brush-in jointing compounds and kiln-dried jointing sand are faster. You brush the dry product into the joints, compact it, and then either brush away the excess or spray with water to activate it. Products like Weatherpoint and similar resin-based compounds set hard and are much more resistant to frost and weed growth than standard mortar. More expensive, but they last well. Worth considering for the whole patio rather than just patching sections.

4. Apply traditional mortar (if that is your choice)

Mix sharp sand and cement at 4:1 by volume with just enough water to make a stiff, workable mortar - not wet and sloppy. It should hold its shape when squeezed in your hand. Use a pointing trowel or a small margin trowel to press the mix firmly into the joint. Work it in well and consolidate it properly rather than just filling the gap loosely.

Finish the joint flush with the surface of the slabs, or very slightly recessed. Avoid a convex or rounded top joint, which sheds water outward and tends to crack as it cures. Keep foot traffic off for at least 24 hours and protect from rain for the first few hours if possible.

5. Apply brush-in jointing compound (if using)

For brush-in products, make sure the joints and slabs are dry first. Pour the compound onto the patio and brush it into the joints using a stiff brush or squeegee. Work it well into every joint. Go over the area a couple of times, pressing the compound down as you go.

Brush off the excess from the slab surface carefully. Most products then need either compacting with a rubber mallet or a light spray of water to activate. Follow the manufacturer's instructions on this - some need one, some need both, and getting it wrong is the most common way to end up with joints that go powdery rather than hard.

6. Clean up and protect while curing

Remove any smears or marks from the slab surface as you go, before they harden. A damp sponge works well on fresh mortar. Once dried, cement residue on stone or porcelain is stubborn and sometimes needs acid cleaning to shift - much easier to deal with it fresh.

Keep the patio clear of foot traffic for at least 24 hours and preferably 48. If rain is forecast within the first couple of hours of laying traditional mortar, cover the area with polythene sheeting. Jointing compounds are generally more forgiving of rain after the first hour or two, but check the product guidelines.

When to call a handyman

Repointing a small patio is a reasonable weekend job for most people. On a larger area, or if the slabs need lifting and relaying before you can repoint, the work adds up quickly. Richard can handle patio repointing and maintenance across Sandwich and East Kent - it is the sort of job that is well worth getting done properly before winter.