Black spots on Indian Sandstone

[Dennis Taylor]

Hi Peeps,

I seem to be picking up more and more Indian Sandstone patios these days and i must say they always look really good when they've been cleaned ( Instant WOW Factor )

I have noticed that quite often some of the flags have black spots on them which i find quite difficult to remove.

My normal hypo mix is around 3-4% which gets the normal flags looking great but still leaves the black spots.

I have tried re-applying more hypo to the spots and using a hard broom to really brush it in, i then leave it a while and re-pressure wash with some degree of success.

What do you guys use ? I have thought about neat 10% - 15% in a small sprayer and just just spot spray the affected area, however im conscious of damaging the sandstone in the process.

Any advise would be much appreciated.

Dennis

 

[kevinc250]

Hi Peeps,I seem to be picking up more and more Indian Sandstone patios these days and i must say they always look really good when they've been cleaned ( Instant WOW Factor )

I have noticed that quite often some of the flags have black spots on them which i find quite difficult to remove.

My normal hypo mix is around 3-4% which gets the normal flags looking great but still leaves the black spots.

I have tried re-applying more hypo to the spots and using a hard broom to really brush it in, i then leave it a while and re-pressure wash with some degree of success.

What do you guys use ? I have thought about neat 10% - 15% in a small sprayer and just just spot spray the affected area, however im conscious of damaging the sandstone in the process.

Any advise would be much appreciated.

Dennis

hi dennis,please don't take the umbridge with me but it would be better to understand what those "black spots" are,applying yet more hypo will not work i'm afraid,if i'm honest i get the jist that you don't really understand sodium hypochlorite and how it works and more to the point what you are working with as in indian sanstone/flags etc in relation to hypo-its not the magic answer to all things i'm afraid

 

[Dennis Taylor]

Hi kev, thanks for taking the time to reply.

i'm always keen to learn from others so no umbridge taken. I assumed that the black spots were a type of lichen that i often find in poor quality concrete slabs, you know.... the sort that seems to bury itself deep within the concrete.

Whilst these black spots also look as if they could be part of the makeup of the sandstone, they still don't look good if left alone ( The job still looks only half done ).

If you are prepared to better inform me then i would really appreciate it.

Best regards

Dennis