National Masonry offers a few useful tips on cleaning and maintaining concrete pavers.
Concrete pavers can pick up common stains over a period of time due to various environmental factors. Efflorescence, for instance, is a salty deposit on the surface of pavers formed as a result of a chemical reaction that takes place during the curing of concrete. Appearing as strong, powdery, white blotches through to a fine white haze, efflorescence can make pavers or blocks look faded. Efflorescence may also occur from salt deposits in adjacent materials such as bedding sand, joint sand or soil.
Though rain will generally dissolve efflorescence and gradually wash it out of the paver or block over time, stubborn patches may require cleaning with a stiff bristled nylon brush or colourless plastic scouring pad. Using deeply coloured or metallic brushes and scourers may leave marks on the concrete surface, and should be avoided.
The cleaning method involves first brushing away the powder residue from the efflorescence patch and then rinsing and brushing the area thoroughly with clean water. Leaving the efflorescence on the paver surface will only result in the residue soaking back in and re-staining the area.
Stubborn efflorescence stains may require stronger solutions such as sealers from reputable manufacturers including ENVIRONEX and Drytreat. Efflorescence cleaners are also available at good landscape supply stores.
Cleaning moss, mould and leaf stains
To clean moss, mould and leaf stains from concrete blocks or pavers, soak the stained area using a domestic bleach or a solution of five parts water with one part pool chlorine. Leave for ten minutes and gently hose down the surface before the solution dries up.
Never use hydrochloric acid to clean concrete pavers as it may cause irreparable surface damage.
Sealing concrete pavers
National Masonry recommends that all pavers should be sealed with a quality penetrating sealer following installation for maximum protection. Consult with a qualified tradesperson for advice on the right sealer.