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Old 27-07-2003, 05:33 PM
Ben
 
Posts: n/a
Default Black mould spots again

I've asked this question before on this group, but having tried people's
suggestions without success I thought it was worth another go.

I have very unsightly black mould spots on the concrete slabs on my
patio and garden path. An ordinary scrubbing brush has no effect, a lot
of hard brushing with a wire brush has limited effect but has now
started ruining the surface of the concrete (without really bringing off
the mould) so I daren't do it any more. Chemicals I've tried without
success include algae removing patio cleaner, jayes fluid (including
neat), bleach (potassium hydroxide type and sodium hypochlorite type -
including neat), sodium hydroxide, and a sodium dichlorophen fungicide.
Any other ideas I could try?

Anyone who would like to suggest that brushing sand into it would work
where wire-brushing the surface of the concrete off has failed is
welcome to come round and try it.


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Old 27-07-2003, 06:13 PM
David W.E. Roberts
 
Posts: n/a
Default Black mould spots again


"Ben" wrote in message
...
I've asked this question before on this group, but having tried people's
suggestions without success I thought it was worth another go.

I have very unsightly black mould spots on the concrete slabs on my
patio and garden path. An ordinary scrubbing brush has no effect, a lot
of hard brushing with a wire brush has limited effect but has now
started ruining the surface of the concrete (without really bringing off
the mould) so I daren't do it any more. Chemicals I've tried without
success include algae removing patio cleaner, jayes fluid (including
neat), bleach (potassium hydroxide type and sodium hypochlorite type -
including neat), sodium hydroxide, and a sodium dichlorophen fungicide.
Any other ideas I could try?

Anyone who would like to suggest that brushing sand into it would work
where wire-brushing the surface of the concrete off has failed is
welcome to come round and try it.

Pressure washers are good for cleaning concrete.
IMHO they are certainly more effective than wire brushing.
They do tend to lift anything loose, but they bring concrete slabs up like
(almost) new.
Perhaps it isn't mould, but just general filth settling in to the fine holes
in the surface of the concrete.
I find our slabs go grimy over the year, but a good blast with the pressure
washer makes them much cleaner.

HTH
Dave R


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Old 27-07-2003, 07:13 PM
Ben
 
Posts: n/a
Default Black mould spots again

David W.E. Roberts wrote:
Pressure washers are good for cleaning concrete.
IMHO they are certainly more effective than wire brushing.
They do tend to lift anything loose, but they bring concrete slabs up like
(almost) new.
Perhaps it isn't mould, but just general filth settling in to the fine holes
in the surface of the concrete.
I find our slabs go grimy over the year, but a good blast with the pressure
washer makes them much cleaner.


It definitely isn't just general filth. On otherwise spotlessly clean
slabs there are black circles about the size of a pea on average that
stand up slightly above the surface as if black paint has been spilled.
On one of the slabs some coloured paint has been spilled at some point
and it gives a very similar effect.

I had resisted using a pressure washer as the patio is just layed
straight onto sand with sand between the slabs and I didn't want to
blast the stuff away, but I guess I'm going to have to give it a try.

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Old 27-07-2003, 07:43 PM
bnd777
 
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Default Black mould spots again

We have the same black mould problem on both patio and stone walls
...........however no amount of pressure washing shifts them ........do not
know what chemical to resort to but sure as hell they need dealing with next
spring ........maybe if i do get them clean i need to seal them all with
Thompsons or something
"David W.E. Roberts" wrote in message
...

"Ben" wrote in message
...
I've asked this question before on this group, but having tried people's
suggestions without success I thought it was worth another go.

I have very unsightly black mould spots on the concrete slabs on my
patio and garden path. An ordinary scrubbing brush has no effect, a lot
of hard brushing with a wire brush has limited effect but has now
started ruining the surface of the concrete (without really bringing off
the mould) so I daren't do it any more. Chemicals I've tried without
success include algae removing patio cleaner, jayes fluid (including
neat), bleach (potassium hydroxide type and sodium hypochlorite type -
including neat), sodium hydroxide, and a sodium dichlorophen fungicide.
Any other ideas I could try?

Anyone who would like to suggest that brushing sand into it would work
where wire-brushing the surface of the concrete off has failed is
welcome to come round and try it.

Pressure washers are good for cleaning concrete.
IMHO they are certainly more effective than wire brushing.
They do tend to lift anything loose, but they bring concrete slabs up like
(almost) new.
Perhaps it isn't mould, but just general filth settling in to the fine

holes
in the surface of the concrete.
I find our slabs go grimy over the year, but a good blast with the

pressure
washer makes them much cleaner.

HTH
Dave R




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Old 28-07-2003, 03:15 PM
andrewpreece
 
Posts: n/a
Default Black mould spots again

You could try phosphoric acid, aka known as brick acid, for cleaning
efflorescence off brick. It theoretically should remove a certain amount
of the surface so should bring it up like new. All entirely at your own risk
though,

Andy.

"bnd777" wrote in message
...
We have the same black mould problem on both patio and stone walls
..........however no amount of pressure washing shifts them ........do not
know what chemical to resort to but sure as hell they need dealing with

next
spring ........maybe if i do get them clean i need to seal them all with
Thompsons or something
"David W.E. Roberts" wrote in message
...

"Ben" wrote in message
...
I've asked this question before on this group, but having tried

people's
suggestions without success I thought it was worth another go.

I have very unsightly black mould spots on the concrete slabs on my
patio and garden path. An ordinary scrubbing brush has no effect, a

lot
of hard brushing with a wire brush has limited effect but has now
started ruining the surface of the concrete (without really bringing

off
the mould) so I daren't do it any more. Chemicals I've tried without
success include algae removing patio cleaner, jayes fluid (including
neat), bleach (potassium hydroxide type and sodium hypochlorite type -
including neat), sodium hydroxide, and a sodium dichlorophen

fungicide.
Any other ideas I could try?

Anyone who would like to suggest that brushing sand into it would work
where wire-brushing the surface of the concrete off has failed is
welcome to come round and try it.

Pressure washers are good for cleaning concrete.
IMHO they are certainly more effective than wire brushing.
They do tend to lift anything loose, but they bring concrete slabs up

like
(almost) new.
Perhaps it isn't mould, but just general filth settling in to the fine

holes
in the surface of the concrete.
I find our slabs go grimy over the year, but a good blast with the

pressure
washer makes them much cleaner.

HTH
Dave R








  #6   Report Post  
Old 02-04-2009, 07:05 PM
Registered User
 
First recorded activity by GardenBanter: Apr 2009
Posts: 1
Smile

Quote:
Originally Posted by andrewpreece View Post
You could try phosphoric acid, aka known as brick acid, for cleaning
efflorescence off brick. It theoretically should remove a certain amount
of the surface so should bring it up like new. All entirely at your own risk
though,

Andy.

"bnd777" wrote in message
...
We have the same black mould problem on both patio and stone walls
..........however no amount of pressure washing shifts them ........do not
know what chemical to resort to but sure as hell they need dealing with

next
spring ........maybe if i do get them clean i need to seal them all with
Thompsons or something
"David W.E. Roberts"
wrote in message
...

"Ben"
wrote in message
...
I've asked this question before on this group, but having tried

people's
suggestions without success I thought it was worth another go.

I have very unsightly black mould spots on the concrete slabs on my
patio and garden path. An ordinary scrubbing brush has no effect, a

lot
of hard brushing with a wire brush has limited effect but has now
started ruining the surface of the concrete (without really bringing

off
the mould) so I daren't do it any more. Chemicals I've tried without
success include algae removing patio cleaner, jayes fluid (including
neat), bleach (potassium hydroxide type and sodium hypochlorite type -
including neat), sodium hydroxide, and a sodium dichlorophen

fungicide.
Any other ideas I could try?

Anyone who would like to suggest that brushing sand into it would work
where wire-brushing the surface of the concrete off has failed is
welcome to come round and try it.

Pressure washers are good for cleaning concrete.
IMHO they are certainly more effective than wire brushing.
They do tend to lift anything loose, but they bring concrete slabs up

like
(almost) new.
Perhaps it isn't mould, but just general filth settling in to the fine

holes
in the surface of the concrete.
I find our slabs go grimy over the year, but a good blast with the

pressure
washer makes them much cleaner.

HTH
Dave R



Neat bleach removed the black spot almost immediately with no staining on my natural stone patio. A bit expensive if you have a large area but effective,.


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