Question 1

Is a pressure washer bad for block paving?

Accepted Answer

It can be, easily. High pressure held close strips the kiln-dried sand out of the joints in seconds — and that sand is what holds a block pavement together. Cleaning is fine at moderate pressure with the lance kept moving, but the joints must be re-sanded and vibrated afterwards, every time. It is worth understanding why, because it explains a common and baffling experience: a drive that looked immaculate the week it was cleaned and was visibly loose six months later. Block paving is held together by friction from the sand packed tight into every joint, pressing against a restrained edge. Empty the joints and the blocks start moving independently under load. The damage is invisible on the day and unmistakable by the following spring. A rotary surface cleaner run at full pressure is the worst offender, because it works fast and covers a lot of ground before anyone notices what it is doing to the joints. A lance held close does the same thing more locally. The technique that works is moderate pressure, the lance kept moving and held back from the surface, and an acceptance that the drive will not go from black to new in a single pass. The other reason to moderate pressure is that blasting removes the visible moss and leaves the spores behind, so a drive cleaned this way is green again within months. Treating with a proper paving biocide first, letting it work, and then cleaning at sensible pressure gives a result that lasts a couple of years instead of a season. Re-sanding is the non-negotiable part. Fresh kiln-dried sand is brushed into every joint and the surface is vibrated with a plate compactor over a protective mat, then topped up and vibrated again until the joints stop taking sand. Brushing sand in without vibrating leaves the joints half full. This step is what restores the interlock, and a cleaning quote that does not mention it is quoting for half the work. Other surfaces have their own limits and they are worth knowing. Resin bound: a close lance damages the mat and can break the bond. Soft or reclaimed sandstone: high pressure erodes the surface permanently. Tarmac: pressure strips the fines and accelerates ravelling. Imprinted concrete: it will take the sealer off, which means resealing. Gravel does not get pressure washed at all.

Question 2

Will jet washing damage my block paving?

Accepted Answer

It can be, easily. High pressure held close strips the kiln-dried sand out of the joints in seconds — and that sand is what holds a block pavement together. Cleaning is fine at moderate pressure with the lance kept moving, but the joints must be re-sanded and vibrated afterwards, every time. It is worth understanding why, because it explains a common and baffling experience: a drive that looked immaculate the week it was cleaned and was visibly loose six months later. Block paving is held together by friction from the sand packed tight into every joint, pressing against a restrained edge. Empty the joints and the blocks start moving independently under load. The damage is invisible on the day and unmistakable by the following spring. A rotary surface cleaner run at full pressure is the worst offender, because it works fast and covers a lot of ground before anyone notices what it is doing to the joints. A lance held close does the same thing more locally. The technique that works is moderate pressure, the lance kept moving and held back from the surface, and an acceptance that the drive will not go from black to new in a single pass. The other reason to moderate pressure is that blasting removes the visible moss and leaves the spores behind, so a drive cleaned this way is green again within months. Treating with a proper paving biocide first, letting it work, and then cleaning at sensible pressure gives a result that lasts a couple of years instead of a season. Re-sanding is the non-negotiable part. Fresh kiln-dried sand is brushed into every joint and the surface is vibrated with a plate compactor over a protective mat, then topped up and vibrated again until the joints stop taking sand. Brushing sand in without vibrating leaves the joints half full. This step is what restores the interlock, and a cleaning quote that does not mention it is quoting for half the work. Other surfaces have their own limits and they are worth knowing. Resin bound: a close lance damages the mat and can break the bond. Soft or reclaimed sandstone: high pressure erodes the surface permanently. Tarmac: pressure strips the fines and accelerates ravelling. Imprinted concrete: it will take the sealer off, which means resealing. Gravel does not get pressure washed at all.

Question 3

Can I jet wash my driveway?

Accepted Answer

It can be, easily. High pressure held close strips the kiln-dried sand out of the joints in seconds — and that sand is what holds a block pavement together. Cleaning is fine at moderate pressure with the lance kept moving, but the joints must be re-sanded and vibrated afterwards, every time. It is worth understanding why, because it explains a common and baffling experience: a drive that looked immaculate the week it was cleaned and was visibly loose six months later. Block paving is held together by friction from the sand packed tight into every joint, pressing against a restrained edge. Empty the joints and the blocks start moving independently under load. The damage is invisible on the day and unmistakable by the following spring. A rotary surface cleaner run at full pressure is the worst offender, because it works fast and covers a lot of ground before anyone notices what it is doing to the joints. A lance held close does the same thing more locally. The technique that works is moderate pressure, the lance kept moving and held back from the surface, and an acceptance that the drive will not go from black to new in a single pass. The other reason to moderate pressure is that blasting removes the visible moss and leaves the spores behind, so a drive cleaned this way is green again within months. Treating with a proper paving biocide first, letting it work, and then cleaning at sensible pressure gives a result that lasts a couple of years instead of a season. Re-sanding is the non-negotiable part. Fresh kiln-dried sand is brushed into every joint and the surface is vibrated with a plate compactor over a protective mat, then topped up and vibrated again until the joints stop taking sand. Brushing sand in without vibrating leaves the joints half full. This step is what restores the interlock, and a cleaning quote that does not mention it is quoting for half the work. Other surfaces have their own limits and they are worth knowing. Resin bound: a close lance damages the mat and can break the bond. Soft or reclaimed sandstone: high pressure erodes the surface permanently. Tarmac: pressure strips the fines and accelerates ravelling. Imprinted concrete: it will take the sealer off, which means resealing. Gravel does not get pressure washed at all.

Is a pressure washer bad for block paving?

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