Commercial jet washing guide
Can you jet wash limestone?
Limestone is widely used for commercial outdoor terraces, hotel courtyards and residential patios across London. It can be jet washed, but it is a calcium-based stone that reacts permanently with acid and is easily damaged by excessive pressure. Getting this wrong leaves marks that cannot be undone.
Limestone is a sedimentary rock composed primarily of calcium carbonate. This composition gives it its characteristic pale tones, cool surface and subtle natural variation, making it a premium choice for outdoor commercial and residential spaces. It also makes it the most chemically reactive of the stones commonly used for outdoor paving. Any acidic substance, however mild, will chemically react with the calcium carbonate and etch the surface, dissolving the mineral structure and leaving permanently dull, rough or discoloured areas. Once the surface of limestone is etched, there is no way to reverse the damage without mechanical re-honing or replacement. Understanding this chemistry before any cleaning begins is not optional. It is the difference between maintaining an expensive stone investment and destroying it.
Below 1,000 PSI
the maximum safe pressure for jet washing most limestone. Many specialists recommend well below this with a very wide nozzle
No acid. Ever
acid reacts chemically with calcium carbonate in limestone and causes immediate permanent etching that cannot be reversed
No bleach
bleach discolours the natural stone minerals in limestone and causes patchy lightening across the surface
The chemistry that makes limestone uniquely vulnerable
Limestone is a calcareous stone, meaning its primary mineral component is calcium carbonate. When any acidic substance contacts calcium carbonate, an immediate chemical reaction produces calcium salts and carbon dioxide. On the surface of the stone, this reaction dissolves the mineral matrix, creating an etched, pitted or dull area that is structurally different from the unaffected stone around it. The reaction is fast, a splash of undiluted vinegar left on polished limestone for a few minutes can produce visible etching. On honed or riven outdoor limestone, the effect is a loss of the characteristic surface texture and a rough, bleached or pitted finish.
Common acidic substances that damage limestone include vinegar, citric acid, standard brick and patio cleaners containing hydrochloric or phosphoric acid, efflorescence removers formulated for concrete, rust removers that are safe for granite but not calcareous stone, and bleach-based cleaners. The STIHL professional guide to natural stone paving explicitly states that vinegar should never be used on limestone. RICS stone specialists classify acid damage to limestone as a category of irreversible surface loss.
Safe jet washing methodHow to jet wash limestone correctly
1. Inspect the stone and jointing before starting
Check the limestone is in structurally sound condition with no loose slabs, cracking at slab faces or failing jointing. Check that the stone has not been previously damaged by acid or previous cleaning attempts. If in doubt, test in a discreet area before proceeding.
2. Apply a pH-neutral or mild alkaline stone cleaner
For contamination beyond general surface dirt, apply a cleaning product specifically formulated as pH-neutral or mildly alkaline for limestone and calcareous stone. Products such as LTP Grimex are widely used by stone specialists. Apply, allow the stated dwell time and do not let the product dry on the stone. Avoid any product marked as acid-based regardless of how it is marketed.
3. Jet wash at below 1,000 PSI with a 40-degree nozzle at 50 to 60 cm
Keep pressure below 1,000 PSI with a 40-degree or wider fan nozzle at a minimum 50 to 60 cm from the stone surface. For softer limestone varieties, many specialists recommend hand washing with a soft brush rather than jet washing at any pressure. Work in overlapping sweeps and keep the nozzle moving constantly. Never concentrate the jet on a single area.
4. Allow to dry fully and apply a breathable impregnating sealer
After the stone has dried completely (allow 48 hours in dry weather), apply a breathable impregnating sealer specifically formulated for natural limestone. This protects against staining, slows biological growth and makes subsequent cleaning significantly easier. Never apply a film-forming or non-breathable sealer to limestone as it traps moisture in the stone.
Commercial jet washing London
Professional limestone cleaning across London by Cloud Nine
Cloud Nine cleans limestone paving on commercial and residential premises across London using only pH-neutral stone cleaners at the correct pressure. We never use acid, bleach or turbo jets on any calcareous stone surface. Contact us for a free quote.
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