I have noticed that many of the indian sandstone slabs I had laid 3
years ago are developing lots of unsightly dark 'spots', as shown in
these images:

http://www.davidwgreen.talktalk.net/DSCF0173.JPG
http://www.davidwgreen.talktalk.net/DSCF0174.JPG
http://www.davidwgreen.talktalk.net/DSCF0175.JPG

These marks cannot be removed by a pressure washer, and appear to reach
down into the stone itself. I started to notice these stains last year,
but this year there are a lot more of them. Not all the slabs are
affected as you can see in the photos. Can anyone tell me what is
causing this problem and what I can do about it? I'm worried that this
will continue getting worse until my entire patio is black! Is there a
name for this problem?

Is this a case of defective stone? Should I be demanding replacement
slabs from the supplier or the company which laid (and supplied) the slabs?

I hope someone can help.

Sincerely,

D Green
Cambridge UK

On Tue, 10 Apr 2007 13:27:37 +0100, David Green
wrote:

I have noticed that many of the indian sandstone slabs I had laid 3
years ago are developing lots of unsightly dark 'spots', as shown in
these images:

http://www.davidwgreen.talktalk.net/DSCF0173.JPG
http://www.davidwgreen.talktalk.net/DSCF0174.JPG
http://www.davidwgreen.talktalk.net/DSCF0175.JPG

These marks cannot be removed by a pressure washer, and appear to reach
down into the stone itself. I started to notice these stains last year,
but this year there are a lot more of them. Not all the slabs are
affected as you can see in the photos. Can anyone tell me what is
causing this problem and what I can do about it? I'm worried that this
will continue getting worse until my entire patio is black! Is there a
name for this problem?

Is this a case of defective stone? Should I be demanding replacement
slabs from the supplier or the company which laid (and supplied) the slabs?

I hope someone can help.

Sincerely,

D Green
Cambridge UK

Looks like a normal lichen growth to me and little you can do except
clean it off every so often, or use chemicals to destroy them.


I think it's the second or third oldest lifeform on earth.

On 10/04/2007 13:51, EricP wrote:

Looks like a normal lichen growth to me and little you can do except
clean it off every so often, or use chemicals to destroy them.

Pressure washer has no effect. How else can I clean it off? And what
chemicals do you recommend to kill it?

David

"David Green" wrote in message
...
I have noticed that many of the indian sandstone slabs I had laid 3 years
ago are developing lots of unsightly dark 'spots', as shown in these
images:

http://www.davidwgreen.talktalk.net/DSCF0173.JPG
http://www.davidwgreen.talktalk.net/DSCF0174.JPG
http://www.davidwgreen.talktalk.net/DSCF0175.JPG

D Green
Cambridge UK


In the third image I can see the same spots on the mortar joints, so it's
not the slabs at fault, are you sure haven't spilt grease (from last years
BBQ) on the slabs.
Not sure how to remove the marks, others have used chlorine to clean patio
slabs but not tried this myself.

F

On Tue, 10 Apr 2007 15:20:29 +0100, David Green wrote:

Looks like a normal lichen growth to me and little you can do except
clean it off every so often, or use chemicals to destroy them.

Pressure washer has no effect. How else can I clean it off? And what
chemicals do you recommend to kill it?

Live with it. Adds natural character and patina to boring clean stone.


--
Cheers
Dave. pam is missing e-mail

On Tue, 10 Apr 2007 22:24:17 +0100 (BST), "Dave Liquorice"
wrote:

|!On Tue, 10 Apr 2007 15:20:29 +0100, David Green wrote:
|!
|! Looks like a normal lichen growth to me and little you can do except
|! clean it off every so often, or use chemicals to destroy them.
|!
|! Pressure washer has no effect. How else can I clean it off? And what
|! chemicals do you recommend to kill it?
|!
|!Live with it. Adds natural character and patina to boring clean stone.

In Yorkshire lichen/algae on York Stone is encouraged, to tone down the
stark yellow colour of the new stuff. The recipe used to be a mixture of
cow muck and soot mixed with water and painted on. The Clean Air Act made
the soot redundant, and the recipe is now Yoghurt mixed with water and
painted on. Both supply nutrients for any spores which land on the stone.
--
Dave Fawthrop sf hyphenologist.co.uk 165 *Free* SF ebooks.
165 Sci Fi books on CDROM, from Project Gutenberg
http://www.gutenberg.org/wiki/Main_Page Completely Free to any
address in the UK. Contact me on the *above* email address.

Dave Fawthrop wrote:
On Tue, 10 Apr 2007 22:24:17 +0100 (BST), "Dave Liquorice"
wrote:

|!On Tue, 10 Apr 2007 15:20:29 +0100, David Green wrote:
|!
|! Looks like a normal lichen growth to me and little you can do except
|! clean it off every so often, or use chemicals to destroy them.
|!
|! Pressure washer has no effect. How else can I clean it off? And what
|! chemicals do you recommend to kill it?
|!
|!Live with it. Adds natural character and patina to boring clean stone.

In Yorkshire lichen/algae on York Stone is encouraged, to tone down the
stark yellow colour of the new stuff. The recipe used to be a mixture of
cow muck and soot mixed with water and painted on. The Clean Air Act made
the soot redundant, and the recipe is now Yoghurt mixed with water and
painted on. Both supply nutrients for any spores which land on the stone.

Algae like a slightly acid environment so a scrub of bleach and a
pressure wash will remove it.

In article ,
"The Simpsons" writes:

"David Green" wrote in message
...
I have noticed that many of the indian sandstone slabs I had laid 3 years
ago are developing lots of unsightly dark 'spots', as shown in these
images:

http://www.davidwgreen.talktalk.net/DSCF0173.JPG
http://www.davidwgreen.talktalk.net/DSCF0174.JPG
http://www.davidwgreen.talktalk.net/DSCF0175.JPG

In the third image I can see the same spots on the mortar joints, so it's
not the slabs at fault, are you sure haven't spilt grease (from last years
BBQ) on the slabs.

Another source would be spillage of lawn fertilizer/weedkiller
containing iron sulphate. If so, phosphoric acid (rust remover)
might help, but I've no idea what it might do to the sandstone,
and it might just push the stain further in or change its colour.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On 11 Apr 2007 14:17:04 GMT, (Andrew Gabriel)
wrote:

|!In article ,
|! "The Simpsons" writes:
|!
|! "David Green" wrote in message
|! ...
|!I have noticed that many of the indian sandstone slabs I had laid 3 years
|!ago are developing lots of unsightly dark 'spots', as shown in these
|!images:
|!
|! http://www.davidwgreen.talktalk.net/DSCF0173.JPG
|! http://www.davidwgreen.talktalk.net/DSCF0174.JPG
|! http://www.davidwgreen.talktalk.net/DSCF0175.JPG
|!
|! In the third image I can see the same spots on the mortar joints, so it's
|! not the slabs at fault, are you sure haven't spilt grease (from last years
|! BBQ) on the slabs.
|!
|!Another source would be spillage of lawn fertilizer/weedkiller
|!containing iron sulphate. If so, phosphoric acid (rust remover)
|!might help, but I've no idea what it might do to the sandstone,
|!and it might just push the stain further in or change its colour.

If the sandstone has a *reddish* tinge, this is caused by oxides of iron
(ferric I think) which is the same stuff as rust, so it might turn the
sandstone white.
--
Dave Fawthrop sf hyphenologist.co.uk 165 *Free* SF ebooks.
165 Sci Fi books on CDROM, from Project Gutenberg
http://www.gutenberg.org/wiki/Main_Page Completely Free to any
address in the UK. Contact me on the *above* email address.

Dave Fawthrop wrote:
On 11 Apr 2007 14:17:04 GMT, (Andrew Gabriel)
wrote:

|!In article ,
|! "The Simpsons" writes:
|!
|! "David Green" wrote in message
|! ...
|!I have noticed that many of the indian sandstone slabs I had laid 3 years
|!ago are developing lots of unsightly dark 'spots', as shown in these
|!images:
|!
|! http://www.davidwgreen.talktalk.net/DSCF0173.JPG
|! http://www.davidwgreen.talktalk.net/DSCF0174.JPG
|! http://www.davidwgreen.talktalk.net/DSCF0175.JPG
|!
|! In the third image I can see the same spots on the mortar joints, so it's
|! not the slabs at fault, are you sure haven't spilt grease (from last years
|! BBQ) on the slabs.
|!
|!Another source would be spillage of lawn fertilizer/weedkiller
|!containing iron sulphate. If so, phosphoric acid (rust remover)
|!might help, but I've no idea what it might do to the sandstone,
|!and it might just push the stain further in or change its colour.

If the sandstone has a *reddish* tinge, this is caused by oxides of iron
(ferric I think) which is the same stuff as rust, so it might turn the
sandstone white.
According to my geologist friend, there is also a lot of manganese in
sandstone.