Commercial jet washing guide
Can you jet wash Indian stone?
Indian sandstone is popular in London commercial and residential settings for its warm colour and natural finish. It can be jet washed, but it is a soft, porous natural stone that etches permanently under acid cleaners and surface-erodes under excessive pressure. This guide covers the safe approach and the products to avoid entirely.
Indian sandstone is one of the most widely used paving materials for commercial outdoor spaces, hotel terraces, restaurant courtyard areas and residential patios across London. Its natural riven surface, warm colour variation and relatively competitive price point make it a popular choice. It is also, however, one of the most commonly damaged paving materials from incorrect cleaning. Indian sandstone is a sedimentary rock formed from compressed sand particles, and this structure makes it notably porous and reactive to both high-pressure water and certain chemicals. Understanding its specific vulnerabilities before cleaning begins is the difference between maintaining its appearance over many years and causing irreversible damage in a single session.
Max 1,500 PSI
safe pressure ceiling for Indian sandstone, above this erodes the surface texture and can permanently pit the stone
No acid
acidic cleaners including vinegar permanently etch Indian sandstone and strip the surface finish, never use them on this stone
No bleach
bleach discolours and lightens Indian sandstone permanently and destroys any sealant that has been applied to the surface
Why Indian sandstone responds differently to other paving materials
Indian sandstone absorbs water readily. Its porosity means that cleaning products applied to the surface penetrate the stone body rather than remaining on the surface as they would on dense concrete or porcelain paving. Acidic products that are commonly used on concrete (such as brick cleaners and certain patio cleaners) react chemically with the calcium compounds in sandstone, dissolving the surface minerals and creating permanent etching that cannot be reversed. Bleach penetrates the stone pores and bleaches the natural iron oxide minerals that give Indian sandstone its characteristic warm red, buff and brown tones, leaving pale or patchy discolouration across the slab. High-pressure water erodes the naturally riven surface texture of the stone, softening the characteristic rippled finish into a smoother, less attractive surface and dislodging grains from the face of the slab.
Safe cleaning methodHow to jet wash Indian sandstone correctly
Step 1: Pre-brush to remove loose material
Before any water is applied, sweep and brush the surface to remove loose dirt, leaf matter, grit and organic debris. This reduces the cleaning load and prevents debris being driven into the joints by the jet.
Step 2: Apply a pH-neutral stone cleaner for stubborn staining
For algae, moss or ingrained grime, apply a stone cleaner specifically formulated and pH-neutral for natural sandstone. Products such as LTP Grimex are widely recommended. Follow manufacturer dilution instructions, allow the stated dwell time and do not let the product dry on the surface. Test on a concealed area first.
Step 3: Jet wash at maximum 1,500 PSI with a 40-degree nozzle
Set pressure to between 1,200 and 1,500 PSI maximum. Use a 40-degree wide fan nozzle at a minimum 45 to 60 cm from the stone surface. For larger areas, a surface cleaner attachment set to the appropriate pressure distributes water more evenly. Never use a turbo or pencil jet nozzle. Work in overlapping horizontal sweeps, always moving the nozzle and never concentrating on one spot.
Step 4: Avoid directing the jet at jointing material
Jet washing aimed directly at joints washes out mortar or jointing sand. Keep the jet moving parallel to the surface and avoid concentrating flow directly into joint lines. After cleaning, inspect joint condition and replace any jointing material that has been lost.
Step 5: Allow to dry fully and reseal
Allow the stone to dry completely, which typically takes 24 to 48 hours in London's climate. After drying, apply a breathable impregnating sealer specifically designed for natural sandstone. This protects against future staining, slows biological recolonisation and makes subsequent cleans significantly easier. Do not use a topical film-forming sealer which traps moisture in the stone and causes it to spall in frost.
What never to use on Indian sandstone
Vinegar and citric acid
These natural acidic solutions are sometimes recommended as DIY cleaners. On sandstone they cause immediate etching that dissolves the surface mineral structure, leaving permanently dulled and roughened patches.
Bleach (domestic or commercial)
Highly alkaline bleach penetrates the stone and bleaches the iron oxide minerals that produce the characteristic colouration of Indian sandstone, leaving white, pale grey or patchy areas that cannot be restored.
Brick cleaners and acid-based patio cleaners
Products containing hydrochloric or phosphoric acid designed for concrete and brick will etch sandstone on contact. Always check pH and stone compatibility before applying any cleaning product to Indian sandstone.
High-pressure concentrated jet
Any turbo or narrow-angle nozzle held at close range will erode the riven surface texture of sandstone, soften the characteristic finish and dislodge grains from the slab face. This damage is irreversible.
Commercial jet washing London
Professional Indian sandstone cleaning across London by Cloud Nine
Cloud Nine cleans Indian sandstone paving on commercial and residential premises across London using pH-neutral stone cleaners at the correct pressure with the correct nozzle. We never use acid, bleach or turbo jets on natural stone. Contact us for a free quote.
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