# Dog urine on sidewalk causes black stain?!? **URL:** \ **Category:** Factual Questions\ **Created:** [July 25, 2013, 12:18am UTC](https://boards.straightdope.com/t/dog-urine-on-sidewalk-causes-black-stain/664439 "2013-07-25T00:18:09Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![TruCelt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/trucelt/32/523_2.png) [@TruCelt](https://boards.straightdope.com/u/TruCelt)\ **Post date:** [July 25, 2013, 12:18am UTC](https://boards.straightdope.com/t/dog-urine-on-sidewalk-causes-black-stain/664439/1 "2013-07-25T00:18:09Z")
The canineCelt got a little over enthusiastic while greeting a neighbor this afternoon and he peed on the sidewalk. (the dog did, not the neighbor.) Anyhoo, I went inside and got a five gallon bucket, filled it with hot water and a healthy dollop of ammonia and poured it over the spot to rinse away the yellow puddle. I then went out for a couple of hours. When I got back the ammonia water puddle had mostly dried, but there was a black spot where the dog had peed. It’s quite a dark black, and looks as if someone had put off a firework there. It is just in the pattern of his puddle and even the drip spots are dark grey so I’m sure this is our fault. So, two questions: Why did it turn black? And How should I clean it? Thanks for any help you can give me. \*Probably irrelevant factoid: This dog has always had the yellowest pee I’ve ever seen. Vet says he’s healthy though. ---
**Author:** ![aceplace57](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/aceplace57/32/3500_2.png) [@aceplace57](https://boards.straightdope.com/u/aceplace57)\ **Post date:** [July 25, 2013, 12:22am UTC](https://boards.straightdope.com/t/dog-urine-on-sidewalk-causes-black-stain/664439/2 "2013-07-25T00:22:20Z")
Bleach will whiten concrete. Scrub well with a broom. Hose off the area first. You don’t want any residual ammonia mixing with the bleach. HD has a concrete cleaner thats really good. It’s usually used when pressure washing driveways but should still work with a broom or brush. ---
**Author:** ![Zulema](https://avatars.discourse-cdn.com/v4/letter/z/db5fbb/32.png) [@Zulema](https://boards.straightdope.com/u/Zulema)\ **Post date:** [July 25, 2013, 12:46am UTC](https://boards.straightdope.com/t/dog-urine-on-sidewalk-causes-black-stain/664439/3 "2013-07-25T00:46:40Z")
That’s weird. My dog has peed on concrete and I’ve rinsed it off without leaving a stain. Do you have well water, hard water, or especially acidic water? ---
**Author:** ![TruCelt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/trucelt/32/523_2.png) [@TruCelt](https://boards.straightdope.com/u/TruCelt)\ **Post date:** [July 25, 2013, 2:02am UTC](https://boards.straightdope.com/t/dog-urine-on-sidewalk-causes-black-stain/664439/4 "2013-07-25T02:02:23Z")
Fairly standard public utility water. It tends to be on the high side for chloramine (the things you learn when you have aquariums!) but ph etc. are not out of the ordinary. ---
**Author:** ![SeaDragonTattoo](https://avatars.discourse-cdn.com/v4/letter/s/df705f/32.png) [@SeaDragonTattoo](https://boards.straightdope.com/u/SeaDragonTattoo)\ **Post date:** [July 25, 2013, 2:08am UTC](https://boards.straightdope.com/t/dog-urine-on-sidewalk-causes-black-stain/664439/5 "2013-07-25T02:08:20Z")
When we have to rinse the sidewalk/street/alley of patient accidents and such at the veterinary hospital, we use 1:32 bleach in a bucket. We never use and don’t even stock ammonia for cleaning anything, because it’s an ingredient in urine. I don’t know for sure, but it might have has something to do with darkening the stain. ---
**Author:** ![miss\_elizabeth](https://avatars.discourse-cdn.com/v4/letter/m/838e76/32.png) [@miss\_elizabeth](https://boards.straightdope.com/u/miss_elizabeth)\ **Post date:** [July 25, 2013, 2:31am UTC](https://boards.straightdope.com/t/dog-urine-on-sidewalk-causes-black-stain/664439/6 "2013-07-25T02:31:56Z")
My dogs have peed on concrete many, many times, and I almost never rinse it, and I have never seen anything like that. Super weird. ---
**Author:** ![Seanette](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/seanette/32/9139_2.png) [@Seanette](https://boards.straightdope.com/u/Seanette)\ **Post date:** [July 25, 2013, 2:40am UTC](https://boards.straightdope.com/t/dog-urine-on-sidewalk-causes-black-stain/664439/7 "2013-07-25T02:40:45Z")
I thought avoiding ammonia for cleanups of urine would be because since ammonia is a component of urine, the lingering smell would tell the offending animal or others “here’s the spot to pee!”. ---
**Author:** ![TruCelt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/trucelt/32/523_2.png) [@TruCelt](https://boards.straightdope.com/u/TruCelt)\ **Post date:** [July 25, 2013, 2:47am UTC](https://boards.straightdope.com/t/dog-urine-on-sidewalk-causes-black-stain/664439/8 "2013-07-25T02:47:54Z")
/Phoebe voice: I know, right?: \phoebe voice I was moving fast, and figured ammonia + water would be the obvious way to dilute/rinse the urine. I’ll put some bleach on in the morning. I’d dearly love to know why this happened though. ---
**Author:** ![SeaDragonTattoo](https://avatars.discourse-cdn.com/v4/letter/s/df705f/32.png) [@SeaDragonTattoo](https://boards.straightdope.com/u/SeaDragonTattoo)\ **Post date:** [July 25, 2013, 3:11am UTC](https://boards.straightdope.com/t/dog-urine-on-sidewalk-causes-black-stain/664439/9 "2013-07-25T03:11:03Z")
> [@Seanette](#): > > I thought avoiding ammonia for cleanups of urine would be because since ammonia is a component of urine, the lingering smell would tell the offending animal or others “here’s the spot to pee!”. Totally. I was just ruminating on whether it might have had something to do with darkening the stain in this case. I have no practical knowledge, since I’ve never used ammonia for cleaning. ---
**Author:** ![TruCelt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/trucelt/32/523_2.png) [@TruCelt](https://boards.straightdope.com/u/TruCelt)\ **Post date:** [July 26, 2013, 11:16am UTC](https://boards.straightdope.com/t/dog-urine-on-sidewalk-causes-black-stain/664439/10 "2013-07-26T11:16:26Z")
OK, so it gets weirder. I was running late yesterday, and so basically just went through the same procedure substituting bleach. Five gallons super hot water (you can make tea from the tap water here) and a large dollop of bleach (about 1 cup) and then poured it over the stain. The spot was completely hydrophobic. It was like the dog had peed rain-ex. I noticed after about a gallon and then slowed the pour to hopefully melt away whatever oil or wax was causing it. No luck; the rinse never touched the stain itself. In one spot, where there’s a chip so that the water pooled in there, it was bubbling a bit, but the stain is still dark. Is there perhaps some sort of concrete sealant that might have been darkened by the urine and maybe dissolved then reformed due to the ammonia? It’s all so strange! ---
**Author:** ![pbbth](https://avatars.discourse-cdn.com/v4/letter/p/f9ae1b/32.png) [@pbbth](https://boards.straightdope.com/u/pbbth)\ **Post date:** [July 26, 2013, 2:15pm UTC](https://boards.straightdope.com/t/dog-urine-on-sidewalk-causes-black-stain/664439/11 "2013-07-26T14:15:14Z")
I think the biggest question here is whether or not the stain is in the shape of Jesus or the Virgin Mary. That might explain why the stain won’t go away! ---
**Author:** ![gnoitall](https://avatars.discourse-cdn.com/v4/letter/g/bb73d2/32.png) [@gnoitall](https://boards.straightdope.com/u/gnoitall)\ **Post date:** [July 26, 2013, 2:25pm UTC](https://boards.straightdope.com/t/dog-urine-on-sidewalk-causes-black-stain/664439/12 "2013-07-26T14:25:53Z")
> [@TruCelt](#): > > OK, so it gets weirder. I was running late yesterday, and so basically just went through the same procedure substituting bleach. Five gallons super hot water (you can make tea from the tap water here) and a large dollop of bleach (about 1 cup) and then poured it over the stain. > > The spot was completely hydrophobic. It was like the dog had peed rain-ex. I noticed after about a gallon and then slowed the pour to hopefully melt away whatever oil or wax was causing it. No luck; the rinse never touched the stain itself. > > In one spot, where there’s a chip so that the water pooled in there, it was bubbling a bit, but the stain is still dark. > > Is there perhaps some sort of concrete sealant that might have been darkened by the urine and maybe dissolved then reformed due to the ammonia? > > It’s all so strange! From the evidence, I have to conclude your dog is pissing oil. 😃 Kinda like the goose that laid golden eggs, except canine and black gold. And not eggs. ---
**Author:** ![aceplace57](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/aceplace57/32/3500_2.png) [@aceplace57](https://boards.straightdope.com/u/aceplace57)\ **Post date:** [July 26, 2013, 5:11pm UTC](https://boards.straightdope.com/t/dog-urine-on-sidewalk-causes-black-stain/664439/13 "2013-07-26T17:11:22Z")
I’ve gotten oil stains off my driveway with Krud Kutter. This should work and it doesn’t kill the grass. Some hardware stores carry it or just let amazon deliver it. > **[Amazon.com: Krud Kutter CE326 32-Ounce Concrete Clean and Etch : Industrial...](https://www.amazon.com/Krud-Kutter-32-Ounce-Concrete-Clean/dp/B001I172C4)** > > Buy Krud Kutter CE326 32-Ounce Concrete Clean and Etch: All-Purpose Cleaners - Amazon.com ✓ FREE DELIVERY possible on eligible purchases