Indian sandstone · Guiseley LS20

Black spot on Guiseley sandstone? Fix it right

Green film, black spot and rust marks on riven Indian sandstone.

By the time we're called to a Guiseley sandstone job, the flags have usually kept their colour under planters and lost it everywhere else — a good sign the stone is fine underneath.

We work Guiseley and the surrounding LS20 postcodes every week, so a Indian sandstone job here is a scheduled call, not a special trip.

Where it goes wrong

What ruins indian sandstone in LS20

1acid washes strip the natural buff/grey tone and leave the stone chalky
2leaving black spot untreated lets the lichen root into the pore structure
3high-pressure rotary picks the softer laminations off the riven face

What indian sandstone actually is

Defining traits in Guiseley

riven, sawn or tumbled natural stone imported in mixed-tone crates
porous surface that drinks water and holds algae in shaded gardens
iron traces in some crates that oxidise into rust freckling
hand-cut edges that give the slab its shadow line

Chemistry

What we use, and why

Neutral-pH biocide first, then a lichen-specific oxidiser only on the black spots — never neat bleach onto Indian sandstone.

Our process

How we clean indian sandstone

Step 1

soft-wash biocide 24 hours before to lift the algal film at root

Step 2

hand-scrub or low-pressure rotary at reduced head pressure for the riven face

Step 3

targeted stain-specific treatment on rust freckling and lichen dots

Step 4

clean rinse and joint check with polymeric or kiln-dried refill as needed

Aftercare

Keeping it right

Sweep leaves weekly through autumn, keep planters off the flags for a week after cleaning, and re-treat biocide every 12–18 months.

Timing

When to book

April to October gives the stone time to dry between passes; autumn cleans on shaded gardens should be paired with a residual biocide.

Typical use: rear garden patios, wrap-around terraces, steppingstone paths, pool surrounds.

Guiseley Indian sandstone FAQs

Do you cover the whole of LS20?: Yes, plus surrounding postcodes on the same round — most Guiseley customers get a same-week visit.
Do you seal Indian sandstone after cleaning?: Only on request — sealing changes the tone, so we walk Guiseley customers through the finish choice on site before booking anything in.
Do you re-sand the joints on sandstone?: Depending on the joint spec we'll top up kiln-dried or polymeric sand at the end; we quote the correct one on site.
Will pressure washing damage my Guiseley Indian sandstone?: It can if you go straight in with a rotary — we soft-wash first and only run reduced-pressure passes on the harder-standing joints.
How long will a LS20 sandstone patio stay clean?: 12–24 months in a shaded Guiseley garden, longer if you sweep leaves off through autumn.