Concrete and stone paving
A hard outdoor surface whose weak point is not the slab but the JOINTS between slabs — which is why the standard advice to blast it with a pressure washer is fenced by an angle.
What not to do
Pressure washer should be avoided for Concrete and stone paving
Best avoided
The available guidance advises against this.
Permitted within the manufacturer's stated limits. Outside them it removes jointing material and marks the surface.
Precautions
- Test on an inconspicuous area first
- Check the manufacturer's instructions
Evidence
Supported
Sources
Cleaning & Maintenance Guidelines — Gardens & Driveways
Marshalls plc · Manufacturer documentation
Relied on for: That power washing used to excess damages the paving and shortens its service life, that the lance must not be directed down onto the paving because that costs jointing material, and that some machines mark wet cast paving. (states this directly)
Precautions
- Test on an inconspicuous area first
- Wear gloves
- Dispose of responsibly
In detail
Paving is durable and the manufacturer says so, and almost every way of damaging it while cleaning goes through the same route: the jointing material. The routine is brushing. Where colour is masked, scrub with warm water and washing-up liquid or an ACID-FREE soap-based cleaner, then wash off until ALL the soap has gone, channelling the run-off to a drain rather than onto planting. Pressure washing is permitted and fenced, and the fence is geometric. Used to excess it shortens the paving's service life. The lance is never pointed straight down, because that lifts the jointing material out; it is held at a SHALLOW ANGLE of no more than thirty degrees across the diagonal rather than along the joints; the setting is low; and the joints are INSPECTED AND REFILLED afterwards, because empty joints are bad for the pavement itself. Acid is the other escalation and it is decided by the stone. Granites, basalts and slates are unaffected. Sandstones vary and some turn ORANGE, because of the iron in them. Limestone and marble must never be acid cleaned — hydrochloric acid dissolves them, which is the same chemistry that etches a marble worktop indoors.
What works
Detergent is safe on, in specific conditions, Concrete and stone paving
Safe only in specific conditions
This is only appropriate within specific limits. Outside those limits, no claim is made.
Only within these limits:
- Structurally sound surfaces only
- Hot water with household detergent and a stiff brush; the aim is physical removal, not killing
- Dry completely within 24 to 48 hours
- Correct the moisture problem first
Named by a state health department among the materials that can be cleaned rather than discarded when mouldy: hard plastic, solid wood, concrete, metal and glass.
Precautions
- Ventilate the area
- Wear gloves
Evidence
Supported
Sources
Minnesota Department of Health · Government or regulator
Relied on for: That concrete among other hard materials can be cleaned if structurally sound, using a stiff brush with hot water and household detergent to remove the physical mould growth. (states this directly)
United States Environmental Protection Agency (EPA) · Government or regulator
Relied on for: That mould is scrubbed off hard surfaces with detergent and water and dried completely. (states this directly)
Why
- Concrete and stone paving is explained by Porous and non-porous surfaces
- Concrete and stone paving is explained by Water purity and aggressiveness
Related
- Concrete and stone paving is commonly affected by Algae
- Concrete and stone paving is commonly affected by Oil and grease on textile
- Concrete and stone paving is commonly affected by Engine oil
Aftercare and prevention
- Pressure washing requires the aftercare Concrete and stone paving
Hacks and claims involving this
- Jet-washing the patio every spring Supported
- Cornflour or talc to draw out an oil mark Supported
Sources for this page
Sources
Cleaning & Maintenance Guidelines — Gardens & Driveways
Marshalls plc · Manufacturer documentation
Relied on for: That routine cleaning is brushing and warm soapy water with an acid-free cleaner rinsed until all soap is gone, that the power lance is held at no more than thirty degrees across the diagonal and never directed down because that loses jointing material, that joints are inspected and refilled afterwards, and that acid must not be used on limestone or marble. (states this directly)