Block Paving Cleaning, Re-Sanding & Sealing

This page exists because block paving is the most common job I do and the one most often done badly. The failure is almost always the same: the drive gets washed, it looks tremendous, and nobody puts the sand back.

Why the joint sand matters more than the blocks

Block paving is a flexible pavement. There is no mortar anywhere in it. What holds it together is friction between the blocks, and that friction only exists because the joints are packed with sand.

When the joints are full, a load pressing down on one block is shared sideways into its neighbours and spread across a wide area of the sub-base. When the joints are empty, that load stays on the one block. Over a few hundred car movements you get rocking, chipped edges where blocks knock against each other, and eventually a visible dip where the entrance takes the most turning.

Weeds are the visible symptom and structure is the real problem. A drive with hollow joints is failing slowly whether or not anything is growing in it.

The clean

Thick moss gets scraped off first. It sounds crude and it saves an hour of standing there trying to dissolve it with water, and it means the surface cleaner is removing dirt rather than mowing a lawn.

The open area is then done with a rotary surface cleaner, which keeps the pass even and stops the striping you get from a lance swung across in arcs. Edges, the course along the kerb and anything around a drain or a manhole get a lance at a wide fan angle from further back.

I work in a consistent direction and overlap each pass. Block paving shows inconsistency more than any other surface because the joints give your eye a grid to compare against, and a missed overlap is visible from an upstairs window for years.

The re-sanding

The surface has to be dry before sand goes in. In July that can be the same afternoon. In February it is usually the following day, and I would rather come back than brush damp sand across a wet drive and leave you with joints that are full for the top ten millimetres and hollow underneath.

Kiln-dried sand is brushed diagonally across the blocks so it drops in rather than skidding along the joint lines. I work it in, let it settle, then go back over it. On a drive that has been empty for years the joints will take a surprising amount, and they will take more again after the first rain, so it is worth keeping half a bag to top up in a month.

Do not use building sand. It is damp, it clumps, it stains the blocks and it never reaches the bottom of the joint.

Stabilising sealer

A joint-stabilising sealer soaks into the top of the sand and binds it into a firm but slightly flexible plug. It is the one sealer I actively recommend on block paving, for three reasons that are easy to check: the sand stops washing out in heavy rain, weed seed cannot get a root into a bound joint, and the drive stays looking done for roughly twice as long.

It is £7.50 a square metre and it needs a separate dry visit, because the sand has to be bone dry when it goes on.

What I would steer you away from on a driveway is a silane-siloxane impregnating sealer. Those are excellent on natural stone, where the job is to stop water soaking into a porous slab. On block paving the job is to bind the joints, and silane-siloxane does not do that. It is the wrong tool sold for the right-sounding reason.

Resin jointing compounds

People ask about the resin compounds that set hard in the joint. On a path or a light-use patio they work well and keep weeds down for years. On a driveway I am more cautious, because they are rigid and block paving is designed to flex. Traffic tends to crack them, and once cracked they let water in and hold it there.

Sunken blocks are not a cleaning problem

If part of your drive has settled, cleaning will make it more obvious rather than less, because a clean uniform surface shows a dip that grime was hiding.

A small dip can be lifted, the sharp sand underneath screeded level, and the blocks put back. That is a separate job and a worthwhile one. If a large area has moved, something in the sub-base has failed, water is probably getting somewhere it should not, and you need a groundworker rather than a jet washer. I will tell you that for nothing rather than take money for a clean that makes the problem more visible.

Colour

Block paving fades. The pigment is through the body of most modern blocks but the top few millimetres take the UV and the traffic, and after fifteen years a red block is a lighter red than it was.

Cleaning takes off the grey film and gives you back the colour that is actually there, which is usually a great deal more than people expect and occasionally slightly less than they hoped. The photographs on this page are all genuine and none of them have been adjusted, which is the only useful way to set that expectation.

The price

£5.50 a square metre, kiln-dried re-sanding included. Joint-stabilising sealer £7.50 a square metre on a separate visit. Moss and algae treatment £1.50 a square metre if you want the regrowth slowed.

Minimum job £150. Quoted in writing from photographs, fixed before I start.