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Question DetailsAsked on 8/21/2014

Reddish stains on steps and sidealk

We are noticing reddish stains on our bluestone steps and on the concrete sidewalk. This winter, we used calcium chloride pellets to melt the ice, but I don't think it is that. Our neighbors are big on chemicals to clean their patio, and use pesticides and poisons to kill anything that might be alive in their yard. Would any of this discolor stone and concrete?

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6 Answers

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Commercial ice-melt grade calcium chloride will commonly have a bit or iron chloride or carbonate in it as a minor components, which can cause rusty spots. Granular fertilizer and weed and feeds have iron compounds - commonly iron sulfate, which definitely make rusty looking orange or reddish-brown spots.


Both have materials that can rust the reinforcing in the concrete, causing rust bleed-through.


Generally, if you have rust on the concrete, in a year or so it will start having popouts at some of the worst spots, exposing the rebar or mesh below.


Since it is occurring in the bluestone too, unless an aggressive acidic cleaner is being used on it, or metal furniture or pots are set on it, fertilizer is likely the culprit. Granular fertilizer staining will be in little pencil-eraser sized dots more or less distributed over the surface; if in lines parallel to the sides or joints in the concrete most likley rusting reinforcing from using ice melt on it.


Other things that can stain both include mulch, iron-containing fertilizers and other soil enrichment additives, bits of matal falling off rusty car underbodies, drips from steel gutters, etc.


If coming from the neighbors, unless their patio or lawn directly abuts your steps and sidewalk, I would expect it to be distributed staining, not distinct spots - distinct spots would be from direct contact with something, not runoff from the neighbor's yard.


My guess - since on steps as well as walk - probably from the ice melt. If you wantto do a definitive test, make a small dam or blister bandage with duct tape or such and a rag or gauze and put a bit of icemelt in it on a part of the concrete you don't see much - even on a side toward the ground level you do not see much) and then wet the icemelt and let it sit a day or two, then see if there is a rusty blotch or stain there.

Answered 3 years ago by LCD

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LCD- Thank you so much for taking the time to give such an intelligent, and detailed response.

Answered 3 years ago by 1960

1
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One other thing I forgot to mention - noticed it walking the dog yesterday - nuts and tree flower buds and berries/seeds can also cause brown staining. - If that is the case, should be general in any area with similar trees, not just your walk.


As I said before, spots would be from granule or individual chemicals or biochemical degradation, stuff being washed from neighbor's yard (like from washing their patio) you would expect to be a spread-out, diffuse stain from general wetting, probably not distinct spots unless they are using a hand sprayer to apply a cleaner or such before washing it off.


If it is basically freckles, I am still going to put my primary bet on fertilizer or minor iron minerals in the icemelt. It is also possible the icemelt is causing a chemical reaction in some of the aggregate, causing it to oxidize from a low-oxygen state like maybe a sulfide. If that is the case, would be expected to occur in street sidewalk and neighbor's concrete too, so you could take a walk and see if this is happening to a lot of people's concrete.


Goodluck - if you do decide to clean it off with a concrete cleaner and hand wire brush, or in extreme cases have it sandblasted, a good double-coat walk and drive sealer applied afterwards, and a washing and overcoat applied (easy DIY job) every couple of years should minimize reoccurrence.

Answered 3 years ago by LCD

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Thank you for another insightful post. The spots are varied in size. My theory is that possibly the calcium chloride (the seller swore it wouldn't stain), may have weakened the original sealant, and made the blue stone more open to staining. There seemed to be more bird poop than usual on the steps this spring (possibly due to the unusual weather patterns). On the sidewalk, the concrete next to the neighbors is loaded spots of varying sizes, that made me wonder if there hadn't been some kind of spillage. Or maybe it was the calcium chloride. No sidewalk on our street has anything near this kind of spotting.

We'll take your advice, and try to get it cleaned and sealed.

Answered 3 years ago by 1960

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Since you say more bird droppings than usual, and similar marks on neighbor's walk but not elsewhere along street, quite possible thst is the cause - is there a chokecherry or mountain ash or such - or even a popular bird feeder - in your yard or neighbor's that they are eating. Birds tend to lighten the load on takeoff, so to speak, so you typically get a lot of droppings in the first 50-100 feet or so around their favorite feeding spots. This is commonly a problem on decks and patios.

Answered 3 years ago by LCD

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We do have a Norwegian Maple out front. I remember a bunch of birds with an unfamiliar cry, not your usual "tweet," or "caw." More aggressive, and annoying I was busy, and didn't have time to do as much cleaning off of porch. They were probably blasting us with who-knows-what.

Answered 3 years ago by 1960

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Doh. I don't know why I didn't think of this earlier.

This Spring, we had brick lintel repairs on our windows. The front window is 4 feet away from the front porch and walk. The porch must have been splashed with chemicals, and never got washed off properly. These brick guys do amazing work on vintage houses, but the damage has proven quite costly.

Answered 3 years ago by 1960




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