Getting rid of acid stains on patio

Ian wrote:

I cam assure you that all my cheap indian sandstome was washed with brick acid, and no stains resulted. Huge algal blooms did, however.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

So ...
once applied, don't eat the paving stones
--
geoff

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
geraldthehamster wrote:

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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Dave Osborne wrote:

Well if its limestomne why call it sandstone?
Indian sandstone is sandstone. AKA fake York stone. IIRC
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
geraldthehamster wrote:

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..
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Dave Osborne wrote:

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!
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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

John.

/=================================================================\
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
John Rumm wrote:

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!
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 17/09/2010 18:31, Dave Osborne wrote:

It was always recommended as a bleach for wood, though I never figured out how it would work.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Dave Osborne wrote:

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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Wed, 22 Jun 2016 08:35:02 -0700 (PDT), snipped-for-privacy@gmail.com wrote:

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

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
If its iron, I wonder if a magnet might be useful? Just a thought. Brian
--
----- -
This newsgroup posting comes to you directly from...
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Dave, thanks for posting this. I too have a sandstone walkway and steps tha t 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 dec k 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 gallon s of water. I did not boil it, as it seemed to dissolve fine with the hot t ap water I used. I did stir it up. I then poured it over the areas and work ed it in with a stiff broom for about 10-15 minutes. I could see most of th e 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 stai ns 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 fe el like it is resolved fully in order to prevent anything else like fertili zer from affecting it. Thanks again for this post.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Site Timeline

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.