Indian Sandstone Patio - Restore colour with Karcher?

JMR · 13-04-2020 03:11PM #1

Patio is in place approx 12 years and is looking very tired, most of the original colour is now faded to a dull grey with a lot of black algae spots.
Any previous attempts to clean it have only resulted in removing the grime and brightening the stones but not shifting the algae and certainly not restoring the colour.

From a small bit of research, it looks like I need a very powerful washer?
I was looking at this Karcher K7

https://www.kaercher.c...s-home-13171360.html

It's quite expensive so was wondering what people's thoughts are?

monkeynuz · 14-04-2020 05:53AM

JMR wrote: »

Patio is in place approx 12 years and is looking very tired, most of the original colour is now faded to a dull grey with a lot of black algae spots.
Any previous attempts to clean it have only resulted in removing the grime and brightening the stones but not shifting the algae and certainly not restoring the colour.

From a small bit of research, it looks like I need a very powerful washer?
I was looking at this Karcher K7

https://www.kaercher.c...s-home-13171360.html

It's quite expensive so was wondering what people's thoughts are?

No, you dont need a really powerful one.

Get some sodium hyperchlorite and apply to pre wet paving at 5:1 initially, brush in then leave for 30 minutes then pressure wash with average power machine, spend a few seconds dwelling on the algae spots. If it doesnt shift it all at once then repeat with stronger solution down to neat.

Btw dont let it dry on the stones.

JMR · 14-04-2020 07:43AM

monkeynuz wrote: »

No, you dont need a really powerful one.

Get some sodium hyperchlorite and apply to pre wet paving at 5:1 initially, brush in then leave for 30 minutes then pressure wash with average power machine, spend a few seconds dwelling on the algae spots. If it doesnt shift it all at once then repeat with stronger solution down to neat.

Btw dont let it dry on the stones.

Thanks for the reply.
Presuming that the sodium hypochlorite is for removing the algae spots, will it do anything to restore the colour of the stone?

monkeynuz · 14-04-2020 07:48AM

JMR wrote: »

Thanks for the reply.
Presuming that the sodium hypochlorite is for removing the algae spots, will it do anything to restore the colour of the stone?

It will do the lot....you will be dazzled by the results, it's quite a shock when you first do it!

monkeynuz · 14-04-2020 07:49AM

Whereabouts are you? Do you have a farm supply place nearby?

Calahonda52 · 14-04-2020 07:50AM

Sodium hypochlorite is alkaline, and household bleach also contains NaOH to make the solution even more alkaline. Two substances are formed when sodium hypochlorite dissolves in water. These are hypochlorous acid (HOCl) and the hypochlorite ion (OCl-), with the ratio of the two being determined by the pH of the water.
Limestone is soft so the HOCI will dissolve the stone if left too long/too strong

monkeynuz · 14-04-2020 08:12AM

monkeynuz wrote: »

No, you dont need a really powerful one.

Get some sodium hyperchlorite and apply to pre wet paving at 5:1 initially, brush in then leave for 30 minutes then pressure wash with average power machine, spend a few seconds dwelling on the algae spots. If it doesnt shift it all at once then repeat with stronger solution down to neat.

Btw dont let it dry on the stones.

When I said neat I meant 1:1

monkeynuz · 14-04-2020 08:13AM

Calahonda52 wrote: »

Sodium hypochlorite is alkaline, and household bleach also contains NaOH to make the solution even more alkaline. Two substances are formed when sodium hypochlorite dissolves in water. These are hypochlorous acid (HOCl) and the hypochlorite ion (OCl-), with the ratio of the two being determined by the pH of the water.
Limestone is soft so the HOCI will dissolve the stone if left too long/too strong

Up to half an hour or so works fine.

JMR · 14-04-2020 08:54AM

monkeynuz wrote: »

Whereabouts are you? Do you have a farm supply place nearby?

I am in Dublin and not surprisingly, I don't even know what a farm supply place is, never mind whether there's one nearby

Household bleach will not do the job, will it?

HeidiHeidi · 14-04-2020 08:58AM

Hi, I replied on your other thread, but this one seems to be getting more traction, so.....

If you want to get rid of the algae spots/staining, I can recommend Algon - I got it in my garden centre, spray it on and leave it to dry in (perfect weather at the moment) and it works over a few days. If the problem is bad, I would guess that a few repeated applications might be needed.

As regards restoring the colour - I really don't see how bleach or chemicals or power washing would do that? I would really love to get the colour back into mine as well, so hoping that someone comes along with a suggestion!

But I think there's two separate problems here......

MarkR · 14-04-2020 09:06AM

I have the same problem, following this with interest. :-)

monkeynuz · 14-04-2020 09:48AM

JMR wrote: »

I am in Dublin and not surprisingly, I don't even know what a farm supply place is, never mind whether there's one nearby

Household bleach will not do the job, will it?

Household bleach will to s point but you'll need much more and it isn't as effective.

Try any hardware stores near you.

monkeynuz · 14-04-2020 09:50AM

HeidiHeidi wrote: »

Hi, I replied on your other thread, but this one seems to be getting more traction, so.....

If you want to get rid of the algae spots/staining, I can recommend Algon - I got it in my garden centre, spray it on and leave it to dry in (perfect weather at the moment) and it works over a few days. If the problem is bad, I would guess that a few repeated applications might be needed.

As regards restoring the colour - I really don't see how bleach or chemicals or power washing would do that? I would really love to get the colour back into mine as well, so hoping that someone comes along with a suggestion!

But I think there's two separate problems here......

Hypochlorite will clean and "restore" the colour, basically it takes the years of staining and discolouration away.

I had avoided doing it for some time as I was rather sceptical about doing it but when I finally did, I only wished I'd done it years ago.

JMR · 26-04-2020 03:15PM

Wanted to follow up on this as I treated the patio with sodium hypochlorite and pressure washed.

I bought 5L of sodium hypochlorite and initially used it a dilution of 3:1, however this didn't provide great results.
I treated again with a more concentrated solution and, while far from new looking, it's a lot better than it was.
Before and after pic attached

monkeynuz · 26-04-2020 03:44PM

JMR wrote: »

Wanted to follow up on this as I treated the patio with sodium hypochlorite and pressure washed.

I bought 5L of sodium hypochlorite and initially used it a dilution of 3:1, however this didn't provide great results.
I treated again with a more concentrated solution and, while far from new looking, it's a lot better than it was.
Before and after pic attached

With regards the black spotting, give it another go and dwell on the black spots with the pressure washer for longer.

Alkers · 26-04-2020 03:44PM

Does the same advice work for the black sandstone?

monkeynuz · 26-04-2020 04:17PM

Alkers wrote: »

Does the same advice work for the black sandstone?

Yes

26-04-2020 04:27PM

Can anyone explain to me how it's bringing back the colour?

My uninformed thought process would have been that direct sunlight would have faded the patio over time, and it'd need to have a 'dye' of sorts applied to colour it again?

HeidiHeidi · 26-04-2020 04:30PM

Deleted User wrote: »

Can anyone explain to me how it's bringing back the colour?

My uninformed thought process would have been that direct sunlight would have faded the patio over time, and it'd need to have a 'dye' of sorts applied to colour it again?

I would like to know this too!

From what I can see, what the OP applied is basically a solution of bleach - how on earth that restores colour in stone is beyond me.

I'm not denying that the stones look far better in the right-hand (I'm assuming that's the "after") picture though.....

Alun · 26-04-2020 04:32PM

Deleted User wrote: »

Can anyone explain to me how it's bringing back the colour?

My uninformed thought process would have been that direct sunlight would have faded the patio over time, and it'd need to have a 'dye' of sorts applied to colour it again?

Indian sandstone is naturally that pink / yellow colour, but over time it gets dirty that's all. The black dots are lichens. They can penetrate into the surface of the stone which is why they're so difficult to remove especially if you leave it too long. If you clean regualarly from the start they won't get a foothold, as it were and are easier to remove.

Frank11 · 27-04-2020 10:01AM

JMR wrote: »

Wanted to follow up on this as I treated the patio with sodium hypochlorite and pressure washed.

I notice the runoff from your stones is to grass. I was worried the bleach/chemical stuff would be damaging to the grass.
Have you noticed any damage?

monkeynuz · 27-04-2020 10:52AM

Frank11 wrote: »

I notice the runoff from your stones is to grass. I was worried the bleach/chemical stuff would be damaging to the grass.
Have you noticed any damage?

It will bleach grass if left but if you are careful you can avoid spraying the grass or wet the grass first with water.

When rinsing the paving you are diluting the solution sufficiently to avoid any discolouration of the grass.

JMR · 27-04-2020 01:51PM

Frank11 wrote: »

I notice the runoff from your stones is to grass. I was worried the bleach/chemical stuff would be damaging to the grass.
Have you noticed any damage?

No damage to the grass, it's fine.
As another poster mentioned, washing it off afterwards dilutes the solution to a relatively harmless level

Alkers · 27-04-2020 03:32PM

IS this stuff available to order / collect anywhere at the moment?

JMR · 27-04-2020 06:00PM

Alkers wrote: »

IS this stuff available to order / collect anywhere at the moment?

I bought from this guy
http://www.doc-solder.ie/store/

Collected in Dublin 11

Indian Sandstone Patio - Restore colour with Karcher?

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