Getting rid of acid stains on patio

[Dave Osborne]

The parents have had a patio laid in Indian sandstone/limestone. Dad
decided to try getting a few mortar stains off with acid-based patio
cleaner. After a week or so, the patio has turned orangey-brown where
the acid has been.

According to paving expert, the acid staining is permanent. :-(

Anybody know if you can get rid of acid staining? Oxalic acid-based
scouring powder seems to be an option, but paving expert cites oxalic
acid as "unproven". Is it worth a go?

Cheers,
DaveyOz

[John Rumm]

Could try it on one spot and see.

Other options include just leaving it - a bit of weathering will blend
it in over time, or acid washing the rest of it to match!

--
Cheers,

John.

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[Dave Osborne]

John Rumm wrote:
> On 10/09/2010 12:04, Dave Osborne wrote:
>> The parents have had a patio laid in Indian sandstone/limestone. Dad
>> decided to try getting a few mortar stains off with acid-based patio
>> cleaner. After a week or so, the patio has turned orangey-brown where
>> the acid has been.
>>
>> According to paving expert, the acid staining is permanent. :-(
>>
>> Anybody know if you can get rid of acid staining? Oxalic acid-based
>> scouring powder seems to be an option, but paving expert cites oxalic
>> acid as "unproven". Is it worth a go?
>
> Could try it on one spot and see.
>
> Other options include just leaving it - a bit of weathering will blend
> it in over time, or acid washing the rest of it to match!
>

I've ordered some Oxalic acid. We'll see whether or not it works.

If I acid washed the rest it would look like Cotswold stone instead of
grey limestone!

[John Rumm]

Do they like the look of Cotswold stone? ;-)

[Jerry]

"Dave Osborne" <Dave...@SPAMymail.com> wrote in message
news:8euhmc...@mid.individual.net...
: The parents have had a patio laid in Indian

sandstone/limestone. Dad
: decided to try getting a few mortar stains off with acid-based
patio
: cleaner. After a week or so, the patio has turned orangey-brown
where
: the acid has been.
:
: According to paving expert, the acid staining is permanent. :-(

He or she is probably correct...

:
: Anybody know if you can get rid of acid staining?
<snip>

Sand blasting, removing the stone to below the level of the acid
damage - a bit 'kill or curer' though...
--
Regards, Jerry.

[The Natural Philosopher]

If it was sandstone, this happened to me too.

It proved too be a lichen of some sort that lurved the acid conditions.

Try caustic soda or bleach and a pressure wash.

After a while, the acid goes anyway and the more usual greeny brown
lichens take over.

[The Natural Philosopher]

sandstone is not damaged by acid.

[Malcolm]

Take care with oxalic acid - it is poisonous. It is the chemical whic
makes rhubarb leaves dangerous.

Malcolm

[stuart noble]

The first thing I'd try is neutralising with washing soda. Not sure why
the acid would have produced a brown colour but the salts of said acid
may wash off more easily.

[Edgar Iredale]

stuart noble wrote:

Iron in the sandstone? Maybe we are dealing with rust.

Edgar

[Ian]

From: stuart noble <stuart...@ntlworld.com>
Date: Fri, 10 Sep 2010 Time: 19:42:28

> Not sure why the acid would have produced a brown colour

It's the action of the acid on ferrous fragments in the stone. See the
para beginning "York Stone" in:

http://www.pavingexpert.com/maintain_02.htm#acid

and the para headed "Concrete Paving" under the pictures.

--
Ian

[Jerry]

"The Natural Philosopher" <t...@invalid.invalid> wrote in message
news:i6dg53$kvj$2...@news.albasani.net...

<snip>
: sandstone is not damaged by acid.

So you are saying that the OP is lying?...

[geraldthehamster]

In how much of a hurry are you? I had some Indian sandstone laid
(always a mistake: if you want a good job done, do it yourself) by a
builder who managed to tread mortar slurry all over the surface, so I
cleaned it off with brick acid, and had just the result you describe.
Two years on, the excess redness has pretty much weathered away.

Cheers
Richard

[Dave Osborne]

Thanks for that Richard; it's nice to know it will weather eventually. I
tried the pressure washer this evening and it seems to have dulled it
down a little. Parents' pressure washer is a bit crap tho'. Will try
with a more powerful PW if the Oxalic acid has no effect.

Just to be clear for the pedants, it is in fact limestone, but it is
(apparently) sometimes called Indian sandstone.

[The Natural Philosopher]

I cam assure you that all my cheap indian sandstome was washed with
brick acid, and no stains resulted. Huge algal blooms did, however.

[The Natural Philosopher]

He never said it was damaged. Merely that it tuned red. Painting it with
red paint turns it red as well.

[The Natural Philosopher]

mine washed out with a pressure washer immediataley.

Though it took several weeks to develop after serious rain and only
developed where the water laid..

[The Natural Philosopher]

Well if its limestomne why call it sandstone?

Indian sandstone is sandstone. AKA fake York stone. IIRC

[geoff]

In message <Elsio.67742$Q_3....@newsfe27.ams2>, Malcolm
<mr...@spam.co.uk> writes

So ...

once applied, don't eat the paving stones

--
geoff

[Jerry]

"The Natural Philosopher" <t...@invalid.invalid> wrote in message

news:i6e9vj$ra0$2...@news.albasani.net...

:

It also damages the surface, especially if it is meant to be -
err - sandstone coloured - and the paint won't come off.

By your 'logic' acid doesn't damage anything, assuming that the
application was intentional, duh! :~(

[The Natural Philosopher]

Jerry wrote:
> "The Natural Philosopher" <t...@invalid.invalid> wrote in message
> news:i6e9vj$ra0$2...@news.albasani.net...
> : Jerry wrote:
> : > "The Natural Philosopher" <t...@invalid.invalid> wrote in
> message
> : > news:i6dg53$kvj$2...@news.albasani.net...
> : >
> : > <snip>
> : > : sandstone is not damaged by acid.
> : >
> : > So you are saying that the OP is lying?...
> : >
> : >
> : He never said it was damaged. Merely that it tuned red.
> Painting it with
> : red paint turns it red as well.
> :
>
> It also damages the surface, especially if it is meant to be -
> err - sandstone coloured - and the paint won't come off.
>
> By your 'logic' acid doesn't damage anything, assuming that the
> application was intentional, duh! :~(
>
>

No. my logic is that a surface coating of lichen is neither a stain, nor
permanent.

OTOH if it wasn't sandstone but limestone, all bets are indeed off. But
limestone fizzes like crazy when you pop acid on it.

[Jerry]

"The Natural Philosopher" <t...@invalid.invalid> wrote in message

news:i6ghau$joo$1...@news.albasani.net...

: Jerry wrote:
: > "The Natural Philosopher" <t...@invalid.invalid> wrote in
message
: > news:i6e9vj$ra0$2...@news.albasani.net...
: > : Jerry wrote:
: > : > "The Natural Philosopher" <t...@invalid.invalid> wrote in
: > message
: > : > news:i6dg53$kvj$2...@news.albasani.net...
: > : >
: > : > <snip>
: > : > : sandstone is not damaged by acid.
: > : >
: > : > So you are saying that the OP is lying?...
: > : >
: > : >
: > : He never said it was damaged. Merely that it tuned red.
: > Painting it with
: > : red paint turns it red as well.
: > :
: >
: > It also damages the surface, especially if it is meant to
be -
: > err - sandstone coloured - and the paint won't come off.
: >
: > By your 'logic' acid doesn't damage anything, assuming that
the
: > application was intentional, duh! :~(
: >
: >
: No. my logic is that a surface coating of lichen is neither a
stain, nor
: permanent.

Whhoooossshhhh.........

[Dave Osborne]

Well, the Oxalic acid worked like magic.

150g/litre in very hot water in a bucket took the stains out in about 10
minutes. I made up 2 litres and by the time I'd used about 1.5 litres,
the water had cooled and there was a load of undissolved stuff in the
bucket. So I added another pint of boiling water and finished off.

100g/litre would probably have been just as good if a little slower.

It leaves little sparkly crystals as it dries, so you need to rinse it
off thoroughly whilst lightly scrubbing with a deck brush.

Note that they (the parents) have dark grey concrete blocks as a border
and these ended up being much lighter afterwards. A further rinse and
scrub (of the edging stones) improved the situation no end and I'm sure
they will weather quite quickly.

Ironically, a further application of brick acid cleaned a sample block
up nicely, I just had to be careful not to get any acid on the limestone!

[John Rumm]

> Well, the Oxalic acid worked like magic.

Result!

There seems something slightly counter-intuitive about correcting the
effects of one acid by application of another.

[Dave Osborne]

John Rumm wrote:
>
>> Well, the Oxalic acid worked like magic.
>
> Result!
>
> There seems something slightly counter-intuitive about correcting the
> effects of one acid by application of another.
>

Well, I haven't even begun to think about the chemistry. The tan colour
just faded away in a few minutes without any fuss or fizzing. As you
say, Result!

[stuart noble]

It was always recommended as a bleach for wood, though I never figured
out how it would work.

[Martin Bonner]

On Sep 10, 3:42 pm, The Natural Philosopher <t...@invalid.invalid>
wrote:

>
> sandstone is not damaged by acid.

The OP has observed otherwise, and Cormaic's pages at pavingexpert.com
also describe the same problem. The various metal salts in the
sandstone can react with HCl to produce a different colour.

Note: I am pretty sure the OP is describing immediate staining, not a
lichen buildup.

[Dave Osborne]

Dave Osborne wrote:
> The parents have had a patio laid in Indian sandstone/limestone. Dad
> decided to try getting a few mortar stains off with acid-based patio
> cleaner. After a week or so, the patio has turned orangey-brown where
> the acid has been.
>
> According to paving expert, the acid staining is permanent. :-(
>
> Anybody know if you can get rid of acid staining? Oxalic acid-based
> scouring powder seems to be an option, but paving expert cites oxalic
> acid as "unproven". Is it worth a go?
>
> Cheers,
> DaveyOz

Well, the Oxalic acid worked brilliantly for a day or three, but the
brown stains have reappeared over the course of two or three weeks. The
stains seem to be more "spread about" and less intense than they were
before.

We just re-treated with Oxalic again this weekend and again, the brown
stains all disappeared within a few minutes. I imagine that the stains
will come back, hopefully less intense again. This could be a longish
term project to gradually get rid of the stains.

[josephdm...@gmail.com]

> Well, the Oxalic acid worked brilliantly for a day or three, but the
> brown stains have reappeared over the course of two or three weeks. The
> stains seem to be more "spread about" and less intense than they were
> before.
>
> We just re-treated with Oxalic again this weekend and again, the brown
> stains all disappeared within a few minutes. I imagine that the stains
> will come back, hopefully less intense again. This could be a longish
> term project to gradually get rid of the stains.

I know this is about 6 years ago now, and the chances of anyone seeing this are slim, but did this eventually work for you? I am in a similar situation.

[Brian Gaff]

If its iron, I wonder if a magnet might be useful? Just a thought.
Brian

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"Chris Hogg" <m...@privacy.net> wrote in message
news:09clmb5u97okghh15...@4ax.com...

> I would suggest that after you've applied the oxalic acid (if you're
> going down that road), flush it well and repeatedly and rinse away the
> flushings, otherwise the iron, which is the cause of the staining,
> will just return, if a little spread out and lighter, as the OP found.
>
> --
>
> Chris

[aaron...@gmail.com]

Dave, thanks for posting this. I too have a sandstone walkway and steps that I got the acid stains on. I was trying to wash some excess mortar off the steps and walkway using a pretty diluted mix of muriatic acid and water. A few days later nasty orange and yellow streaks and spots showed up where I believe the acid sat too long or didn't get washed off well.
After power washing, bleaching, and other methods I thought I was going to have the remove the yellowed stones. Today I purchased the oxalic acid in a crystal powder form from a local paint store. They are selling it as a deck brightener. I put some hot water in a bucket and dumped some oxalic acid in. I'd guess I put in about two to three cups of powder for about 2 gallons of water. I did not boil it, as it seemed to dissolve fine with the hot tap water I used. I did stir it up. I then poured it over the areas and worked it in with a stiff broom for about 10-15 minutes. I could see most of the stains dissolve about 10 minutes into it and some spots took longer. The water/oxalic acid mix would yellow as it lifted the rust/muriatic acid stains off. I then power washed the entire area really well. The yellow stained stones looked as good as new! I'm guessing like Dave posted that they may return and it will need another washing. I plan to seal the patio once I feel like it is resolved fully in order to prevent anything else like fertilizer from affecting it.
Thanks again for this post.

[Craig S]

replying to Dave Osborne, Craig S wrote:
Hi Dave, I've just finished laying 46m2 and cleaned off the cement with what
I thought was limestone/sandstone friendly cleaner. This was not the case and
I've end up with brown stains, almost a rust colour. I've ordered some oxalic
acid and plan to carry out the same as you did on Monday. Can you confirm if
your parents slabs are still ok and the stains have not come back please. I'm
gutted as so much hard work has gone into this! Regards Craig

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[KB]

replying to aaronschoen, KB wrote:
Out of interest did the staining come back. I'm also in a similar situation.
I followed your steps above and with in hours the staining is back, as you say
less aggressive and more spread out. I'd be interested to know how many
washes it took to remove it completely.

[Shanna]

replying to Dave Osborne, Shanna wrote:
Did the oxalic acid work

[Fredxxx]

On 25/10/2017 00:14, Shanna wrote:
> replying to Dave Osborne, Shanna wrote:
> Did the oxalic acid work

Do you think after a mere 7 years the OP will remember?


This might assist you with posting to a newsgroup, albeit through a website:
https://tools.ietf.org/html/rfc1855

- If you are sending a reply to a message or a posting be sure you
summarize the original at the top of the message, or include just
enough text of the original to give a context.

[bm]

"Fredxxx" <fre...@nospam.com> wrote in message
news:osoi94$ht7$1...@dont-email.me...

> On 25/10/2017 00:14, Shanna wrote:
>> replying to Dave Osborne, Shanna wrote:
>> Did the oxalic acid work
>
> Do you think after a mere 7 years the OP will remember?

Does anyone care?

Ohhhhhh, Dave might, he's a real Brit.

[Rod Speed]

"Fredxxx" <fre...@nospam.com> wrote in message
news:osoi94$ht7$1...@dont-email.me...

> On 25/10/2017 00:14, Shanna wrote:
>> replying to Dave Osborne, Shanna wrote:
>> Did the oxalic acid work
>
> Do you think after a mere 7 years the OP will remember?

Bet he does if he isnt dead or ended up with altzhiemers.

[Cal]

replying to KB, Cal wrote:
hi, I too am in this mess, first wash of the limestone with Oxalic Acid
removed the stains but unfortunately they are back after a few weeks, as
mentioned in other responses they are less intense BUT still there. I am now
on the second wash with the Oxalic Acid so hopefully this will reduce it
further, otherwise I am going to keep the process going and hope that it helps

[northst...@gmail.com]

hi did the stains go ?

[Brian Gaff]

Is this only a year old?
Must be a record from home owners consite.
Brian

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<northst...@gmail.com> wrote in message
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[rob]

York stone is sandstone

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[Spike]

rob <53d10e33d9818293...@example.com> wrote:

> York stone is sandstone

York(shire) sandstone? As laid down in a marine environment?

Climate Change is a right bugger, innit.

--
Spike

[Brian Gaff]

So why do we see lots of councils making things look like York Stone. OK my
patio is like that but that is for contrast reasons. Getting acid stains
off, hard but a pressure washer was used on mine carefully though some of
the cracks between slabs needed some attention afterwards.

--

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