removing black walnut stains on masonry ???

I'd be wary of bleach. Might make a different stain,

Contact the company that installed the driveway. My guess this is a common question for them. They may have sealed the surface already.

Let us know what works.
 
Bleach will actually "set" certain organic stains.
(e.g. bodily fluids; wash first, then bleach)

I would spot test with hydrogen peroxide.

per Wikipedia:
Hydrogen peroxide is most commonly available as a solution in water. For consumers, it is usually available from pharmacies at 3 and 6 wt% concentrations. The concentrations are sometimes described in terms of the volume of oxygen gas generated; one milliliter of a 20-volume solution generates twenty milliliters of oxygen gas when completely decomposed. For laboratory use, 30 wt% solutions are most common. Commercial grades from 70% to 98% are also available, but due to the potential of solutions of more than 68% hydrogen peroxide to be converted entirely to steam and oxygen (with the temperature of the steam increasing as the concentration increases above 68%) these grades are potentially far more hazardous, and require special care in dedicated storage areas. Buyers must typically allow inspection by commercial manufacturers.

Check Fisher Scientific, for Lab Supplies.

The walnut liquid has probably been absorbed into the concrete.
Muriatic Acid is hydrochloric acid (HCl), this will dissolve the concrete.
But it may create a divet, and will change the texture of the concrete.

If you do it quickly, I would try grinding some kitty litter (with your foot) into the spot.
It may extract some out of the concrete. (It works well with oil spots, etc on concrete.)
 
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Good luck on that. When I was a kid I made the mistake of hulling black walnuts without any rubber gloves on. My hands were stained for months.
 
I'm in the same boat Daniel. But with black cherry berry stains. Won't come out and now the customer is bending me over a barrel.
 
GregManning said:
Muriatic Acid is hydrochloric acid (HCl), this will dissolve the concrete.
But it may create a divet, and will change the texture of the concrete.
Click to expand...
Partially correct. Muriatic will soften mortar, but not enough to eat a hole (divot) into a concrete block that has already been fired in a kiln. When I used to work for a mason, we would use a Muriatic solution to scrub patios, driveways, etc after installing to get any excess mortar off the faces of the stones/blocks/bricks, leaving it just in the spaces between the blocks as intended. No, I don't remember what % solution we were using.

Best advice so far? Check with the driveway installer. They probably know right away what to use.
 
Sorry, but ...................... Hydrochloric acid will dissolve the concrete until all of the acid is neutralized.
It will not eat a hole to the center of the earth. ;-)
It will also dissolve any limestone, if combined into the concrete mix.
It will not dissolve river rock (aggregate), sand (silica), or kiln fired brick.

My thought was .............. the stains have been absorbed down into the concrete.
If you keep adding acid to get to the bottom of the stain, you will have a shallow divot.

And it will certainly etch the concrete surface.
 
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PPS --- Your customer will not like this approach.

However, in the fall I get leaf stains (as they start to decay, and leach out pigments) on my concrete drive.
A relatively short time later, UV sunlight bleach the stains away.

Just a Guess: The walnut stains may take a longer time; but UV sunlight oxides a LOT of stuff.
 
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