Sandstone
A siliceous stone that mostly shrugs off acid — except where its own iron content reacts, and then acid washing turns the paving orange.
What not to do
Hydrochloric acid is unsafe on Sandstone
Best avoided
The available guidance advises against this.
Precautions
- Test on an inconspicuous area first
Evidence
Supported
Sources
Cleaning & Maintenance Guidelines — Gardens & Driveways
Marshalls plc · Manufacturer documentation
Relied on for: That sandstones vary under acid washing and that some turn orange because of their iron content. (states this directly)
In detail
Sandstone is a sedimentary rock of quartz grains bound by a natural cement, which puts it in the siliceous family rather than the calcareous one. Siliceous stone is mainly silicate and generally acid-resistant, so the rule that governs marble and limestone does not apply directly to it — although the stone trade still discourages acidic cleaners on it as a matter of practice. The specific warning comes from a paving manufacturer, and it is the useful one for anybody with a patio: acid washing is material-dependent, granites, basalts and slates are unaffected, and sandstones vary, with some turning ORANGE because of the iron in them. The iron minerals distributed through the stone are attacked by the acid and oxidise, which is a permanent colour change across a whole slab rather than a stain in one place. Sandstone is also porous enough to take up oil readily, which is why the same guidance says an oil spill should be lifted promptly with an absorbent — paper towel, cat litter, cornflour or talc — and must not be wiped, because wiping drives it in and spreads it.
Properties
Sensitivity
- Acids
- Sources disagree
- Alkalis
- Not known
- Chlorine bleach
- Not known
- Abrasion
- Sensitive
- Porous
- Sensitive
“Not known” means nobody has established this, not that the material is unaffected.
Why
- Sandstone is explained by Porous and non-porous surfaces
- Sandstone is explained by Capillary absorption
- Sandstone is explained by Surface roughness
Related
- Sandstone is commonly affected by Moss and lichen
- Sandstone is commonly affected by Oil and grease on textile
- Sandstone is commonly affected by Algae
- Sandstone is commonly affected by Engine oil
Hacks and claims involving this
Sources for this page
Sources
Cleaning & Maintenance Guidelines — Gardens & Driveways
Marshalls plc · Manufacturer documentation
Relied on for: That acid washing is material-dependent, that granites, basalts and slates are unaffected, that sandstones vary and some turn orange from their iron content, and that oil spills are lifted with an absorbent and must not be wiped. (states this directly)
Care & Cleaning of Natural Stone
Natural Stone Institute · Trade or professional body
Relied on for: That siliceous stone is mainly silicate and generally acid-resistant, though acidic cleaners are still discouraged. (states this directly)