Sandstone cladding (ashlar) is generally maintenance free under normal conditions. A patina of air borne dirt will gradually build upon the surface over a period of time and may lodge in the pores and matrix of the sandstone and cause a graying effect.
In Sandstone paving however this effect will happen at a quicker rate as pollution and air borne particles will settle more readily. This condition will be worse where vertical surfaces discharge onto paved sandstone areas depositing built up dirt and particles.
The influence of algae growth will also have a blackening effect on the colour of sandstone over time. Naturally occurring algae will grow readily in the pores of sandstone especially if moisture is present and in the right environmental conditions may progress into more aggressive lichen growth. In particular the south side of your cladding or paving where the drying effect of the sun is not direct algae will be naturally encouraged to grow.
Tannins from overhanging vegetation, especially eucalypts, will also temporarily darken the surface and encourage algae growth.
It is difficult to prevent the above natural effects from influencing the look of your sandstone installation however the following common sense procedures will assist.
Regular brooming the surface or washing with hose pressure water, if available, will gently remove the build up of surface particles and discourage the algae growth.
Remove overhanging vegetation that is likely to drop leaves, gum nuts etc onto the paving.
Maintenance of the surface drains will ensure quicker disposal of rain water etc.
Maintain gutters and downpipes to preclude overflow onto cladding and paving.
Useful chemicals for cleaning sandstone are either ‘chlorine’ active cleaners like your household bleach, pool chlorine or “Domestos” and “Wet & Forget” which is a microbial biocide. Both these products will work to kill the algae growth but are not eco friendly products and as such should be used sparingly and with caution as the residual product may be washed into your garden or down the drain into the local water system.
Wet & Forget™ is a useful product to inhibit the growth of algae in the first place and does have a residual effect in that it may work effectively for many months.
‘Chlorine’ is generally a faster acting agent and if used by ‘bucket and sponge’ application will remove lichen and algae almost instantly. The chlorine will not affect the sandstone and by ‘sponging’ off the residual dead algae will leave the stone looking like new again. (Wastes should be disposed via the household drainage system ie the laundry sink, not through the stormwater systems ie the surface drain outside your house.)
Using ‘High Pressure Washing’ (ie your household ‘gerni’) can be useful to blast away the build up dirt and algae but extreme care must be exercised not to ‘blast’ the surface of the sandstone. The temptation to get the job done quicker by aiming the nozzle closer to the stone surface often results in the stone being abraded by the blast of the pressure washer, the surface will be cleaned by abrasion however it will be irreparably damaged. We would advise a sample area be undertaken prior and the distance of the nozzle from the stone be examined BEFORE proceeding with this technique.
For removal of artificial contaminants such as oil, paint, glue, marker pen etc we would recommend a professional cleaner be consulted, particularly a company who has had experience with graffiti removal from sandstone. We would be only to pleased to give advice in this regard and we would request you contact us before the application of acids or alkalis (proprietary cleaning agents and paint strippers).
We offer the following guidelines for removal of small stains :
| SOURCE | REMOVAL TECHNIQUE |
| Hardwood/Tanin | Wash and scrub with a solution of 3 parts clean water to 1 part pool chlorine or clear household bleach. Repeat if necessary then rinse with clean water when stain removed. |
| Grease/Oil | Wash and scrub with household detergent or if necessary industrial grade detergent and hot water. Adjust & repeat if necessary. Rinse with clean water when stain removed. |
| Paint | Do not use solvent. Instead, use a proprietary brand paint striper & wash with clean water. If unsuccessful, abrade painted surgace with carborundum stone or sanding papers. |
| Alage | As per instruction for Tanin, but dilute chlorine solution to 5 parts water to 1 part chlorine. |
| Organic Soil | As per Algae above |
| Cement | Apply 1 part Hydrochloric Acid (Muriatic Acid) to 15 parts clean water. Once effective, rinse with clean water. Repeat if necessary. Do not use this method on “Piles Creek” sandstones, unless you consult with Gosford Quarries first. |
| Rejuvenation | As per Algae. Repeat if necessary. If satisfactory result is not achieved, consult a professional stone cleaner. |