# Proper method for cleaning sandstone



## Different Strokes

I have been asked to clean the outside of a stone chimney(chimney sticks about 5 feet out of the middle of the roof. . Appears to be made of sandstone. I'm guessing that since it's the outside of the chimney, i'm not dealing with soot but more of a black algae. Will a mixture of sodium hypochorite and water do the trick? I cleaned a couple small sandstones using regular roof mix at my parents place, but this is for a customer and feel better asking. . 

I would think to prewet the stone, and scrub the mix on would be a good start. any suggestions are appreciated concerning mix ratio, dwell time, rinsing?


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## daArch

for what it's worth, the time tested method of cleaning the bricks inside a fireplace is to use muriatic acid. 

Don't ask me the procedure, all I know is that's what my mother used to do.


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## Lambrecht

Bleach and water. It is very difficult to removes stains from sandstone. You may have to do several cleanings to get decent results. Do not try to paint this type of stone since it is a " self-cleaning" stone and will continually shed it outer layer.


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## PressurePros

You are probably going to have to go with a strong mix. maybe as much as straight household bleach. Start with 1/3 that strength. Careful of your plants (and face)


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## Different Strokes

PressurePros said:


> You are probably going to have to go with a strong mix. maybe as much as straight household bleach. Start with 1/3 that strength. Careful of your plants (and face)


Is a good rinsing needed on stone, or can it be scrubbed on and left for the rain?


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## PressurePros

Different Strokes said:


> Is a good rinsing needed on stone, or can it be scrubbed on and left for the rain?


I'd rinse it. Bleach can leave salts and residue. You'll know right away if you are getting the strength right. Use a flood style nozzle on your machine. (#30 orifice on a 4 gpm, 0-25 degree to get the height you need)


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## boman47k

What precaution need to be put in place concerning the roof in a situation like this? Keep it well rinsed? Cover it? Depending on procedure and mat's used?


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## straight_lines

If you are using straight household bleach I would say you will end up cleaning the roof as well because there will be a clean spot where you cleaned the limestone. Even if you kept it wet to avoid streaking.


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## Roof Cleaning

Always have used a moderate strength water/bleach mix on sandstone.
Pre-wet everything, if you are worried about overspray you could brush it on the tough shots.

Black algae always is a tougher stain to remove than the green stuff down here in FloriduH!


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## Different Strokes

Don't have a pic of the sandstone, but here is the chimney I did across the street from the sandstone. The Neighbor yelled out of the window, so I cleaned hers too. Thanks for the advice everyone. And yes, I warned the lady that there would be clean tiles on the roof from runoff. She was fine with that. I'm going back Next week to finish cleaning the roof


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## PressurePros

Very nice! You wouldn't get that result from pressure washing. The power of bleach.


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## Martinez

Different Strokes said:


> I have been asked to clean the outside of a stone chimney(chimney sticks about 5 feet out of the middle of the roof. . Appears to be made of sandstone. I'm guessing that since it's the outside of the chimney, i'm not dealing with soot but more of a black algae. Will a mixture of sodium hypochorite and water do the trick? I cleaned a couple small sandstones using regular roof mix at my parents place, but this is for a customer and feel better asking. .
> 
> I would think to prewet the stone, and scrub the mix on would be a good start. any suggestions are appreciated concerning mix ratio, dwell time, rinsing?


 My friend just spray it down with pool clorox first and wait 5 min. then spray it down with pressure washer or rinse it down with black tip.


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## Homer

*Be careful if you use muriatic acid*

if you do only use about a 5% solution.

In the early 80's the US Department of the Interior (the people who oversee historic brick restoration) adopted my program which included using hydrofluoric acid rather than muriatic. This product leaves a cleaner clean and does not etch or dissolve the substrate. It is not readily available in most areas but if you can find a contractor who washes fleets of trucks chances are he will have some since it is also use to brighten aluminum rails on commercial vehicles.

Another method - especially if it is sand stone - is the 'Two-Step' or 'Twin Chem' the surface to be cleaned. This is another cleaning procedure that I developed in the early 70's and is probably the most widely used process in the truck washing/fleet cleaning industry. It also works great in the house washing/stone cleaning industry.

With this project I would probably use a phosphoric base product and down-stream the product on the surface and come right back over the top with a medium pH detergent (non-caustic). What happens is this - when the alkali comes in contact with the acid a chemical reaction occurs and during that process the pollutant is lifted off the surface without the use of high pressure or 'scrubbing.' Afterwards a quick rinse will complete the job. If you have quesitons you can contact me at [email protected] - leave your phone number and we can talk further.

Be careful with pressure if it is sandstone and try and stay away of muriatic acid if you can.

Hope this helps.

John
http://www.envirospec.com


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## goodfellow

*Cleaning Sandstone*

A good way to clean sandstone is to use a chlorine solution and blot the dirt/ film away. You need to be very careful not to damage the face of the sandstone and always avoid abrasive materials.
www.sandstonerepairs.com


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