Re-point patio slabs

Rake out old mortar from patio joints, then repoint with fresh mortar or jointing compound for a neat, weatherproof finish.

RP-01Check the weather and pick your dayRepointing needs a dry, mild day, ideally 5-25°C, with no rain forecast for 24 hours after you finish. Frost stops mortar setting properly, so don't work below about 5°C. Check the forecast before you start and clear your whole session, this isn't a job you can leave half done overnight.

RP-02Gather tools and protect yourselfWear gloves and safety goggles, old mortar chips and cement dust fly up as you rake out joints. Knee pads make a long session much easier on hard slabs. Keep a dust mask handy if you plan to use a grinder to cut out stubborn old joints.

1 pair · Work gloves

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1 each · Safety goggles

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1 pair · Knee pads

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1 pack · Dust mask (FFP2)

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RP-03Rake out the old jointsUse a plugging chisel and club hammer, or a purpose-made raking tool, to clear loose or crumbling mortar down to about 20mm deep. Work along each joint in short strokes rather than one long scrape, this stops you chipping the slab edges. If the old mortar is very hard, an angle grinder with a diamond blade cuts it out faster, but wear a dust mask and eye protection, this throws up a lot of fine dust.

1 each · Plugging chisel

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1 each · Club hammer

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1 each · Patio raking tool

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1 each · Angle grinder diamond blade

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RP-04Clear out debris and weedsBrush all loose material, sand and weeds out of the joints with a stiff wire brush. Hook out anything stuck in corners with a narrow trowel or old screwdriver. Rinse very dusty joints with a hose and let them dry fully before you point, damp joints stop new mortar bonding properly.

1 each · Wire brush

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1 each · Stiff outdoor broom

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RP-05Mix mortar or prepare jointing compoundFor a traditional mix, use 1 part cement to 4 parts sharp sand, mixed to a firm, not sloppy, consistency. For an easier job, use a pre-mixed patio pointing compound, either a semi-dry brush-in type or a pourable resin jointing compound, and follow the bag instructions exactly. Mix only as much as you can use in 30-40 minutes, mortar goes off fast.

25 kg bag · Sharp sand

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25 kg bag · Cement

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1 20kg bag · Patio jointing compound

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1 each · Mixing bucket or tub

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RP-06Dampen the slabs if using wet mortarIf you're using a sand-cement mix, lightly dampen the slab edges and joints with a brush dipped in water first. This stops the slab pulling all the moisture out of the mortar before it sets. Skip this step entirely if you're using a resin or brush-in jointing compound, those go in dry.

RP-07Push mortar into the jointsUsing a pointing trowel, press mortar firmly into each joint, working in short sections so it doesn't dry out before you finish shaping it. Overfill slightly, you'll cut it back once it firms up. Keep the trowel clean between loads so mortar doesn't smear across the slab faces.

1 each · Pointing trowel

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RP-08Shape and finish the jointsOnce the mortar has firmed up enough to hold its shape, usually 30-60 minutes depending on the weather, run a rounded jointing tool or a short offcut of hose along each joint. This compresses the mortar, seals it against the slab edges and leaves a neat, slightly recessed finish.

1 each · Jointing tool or hose offcut

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RP-09Brush off excess and clean the slabsOnce the mortar is firm but not fully hard, brush any smears off the slab faces with a soft brush. If cement has dried onto the surface, a light sponge and water wipe now saves a lot of scrubbing later, it's much harder to shift once rock hard.

1 each · Sponge

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RP-10Protect the new pointing while it curesKeep the area free of foot traffic and pets for at least 24 hours, and longer before vehicles or heavy furniture go back on it. Cover the patio with a plastic sheet or tarpaulin if rain is forecast within 24 hours, so it doesn't wash out the new joints. Full strength takes about a week, so treat it gently during this time.

1 each · Plastic sheet or tarpaulin

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RP-11Clean up tools and siteRinse trowels, buckets and mixing tools before mortar sets hard on them, cement comes off far easier wet than dry. Sweep up any leftover sand or debris from the patio and nearby beds. Store unused cement somewhere dry, it goes off if it gets damp.

KNOW THE RULES

Before you start: Do I need permission for a new driveway or dropped kerb?

PART OF A BIGGER PROJECT

Fix up a patio and paths

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