Indian sandstone · Bradford BD1

Black spot on Bradford sandstone? Fix it right

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

Indian sandstone in Bradford gardens tends to darken from the north-facing edge inwards — that's algal, not staining, and it wants chemistry first.

We work Bradford and the surrounding BD1 postcodes every week, so a Indian sandstone job here is a scheduled call, not a special trip.

What indian sandstone actually is

Defining traits in Bradford

Where it goes wrong

Our process

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

Chemistry

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

Timing

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.

Aftercare

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

Is the biocide safe around pets and planting?: Yes at working dilution — we rinse thoroughly and ask for pets to stay indoors for an hour after treatment.
How long will a BD1 sandstone patio stay clean?: 12–24 months in a shaded Bradford garden, longer if you sweep leaves off through autumn.
Do you seal Indian sandstone after cleaning?: Only on request — sealing changes the tone, so we walk Bradford customers through the finish choice on site before booking anything in.
Can you get the black spot off completely?: We treat the lichen dots individually after the main clean; most fade heavily but on porous stone a few ghost marks are honest to expect.
Will pressure washing damage my Bradford 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.