What caused the corrosion on all this piping?
April 9, 2016 4:28 PM   Subscribe

Any thoughts on what could cause uniform surface corrosion on different types of metal inside a bathroom vanity?

I am a plumber and on a recent service call was tasked with dealing with a leak inside a bathroom vanity. I found no leak, just a stain in the bottom of the cabinet. However, all the metal inside the cabinet was corroded. The shutoffs, trap, and supply tubes (brass), and the copper were corroded and had patina. The escutcheons, and more troubling, the braided "stainless" lines connecting the three piece faucet were completely rusted.

I spoke with a coworker who told me he had seen something similar when a dripping faucet was uncorrected for a long duration and condensation formed on all the piping. The homeowner told me that the faucet had dripped for a while, but it was years ago. I inspected again and found that the hinges and hardware for the vanity were similarly corroded. With this in mind, I don't think a leaky faucet is the culprit. I should also note that there is a shower in the bathroom, but they do not use it.

The homeowner does store cleaning supplies and chemicals (Drano in particular, others undetermined as she had cleaned out the cabinet in advance) in the cabinet, and I'm curious if a spill of one or several; or fumes from not-quite-closed bottles could have caused this corrosion. I'm no chemist though so hopefully someone who IS, or someone who has seen this before could help me confirm or debunk this conclusion.
posted by hafehd to Home & Garden (10 answers total)
While high humidity will corrode steel; lightly or poor chromed steel and "stainless" (which is often just barely stainless) it won't corrode brass. The brass will darken or get a bit greenish depending on which kind of brass it is but it won't be so corroded that it pits or becomes rough. (that's assuming it is actually brass and not brass plated)

However an acid will eat away at copper and brass (and steel and chrome). The common household source is bleach. While a leaky/unsealed bottle could cause it I've seen it a couple times where the home owner regularly used bleach in their wash bucket and then didn't rinse out the cloth instead hanging it on the edge of the bucket to dry. Over the course of a few months the weekly drying of the bleach impregnated cloth inside the unventilated vanity ate away at the plumbing.

There is another source: drywall contaminated with sulphur. If the house was built or renovated in the 2000s this may be the issue.
posted by Mitheral at 5:23 PM on April 9, 2016 [3 favorites]

Maybe chinese drywall? In 2006 after Hurricane Katrina a lot of that tainted drywall was installed into flooded homes. Did they have any remodeling done around that time?
posted by JujuB at 5:25 PM on April 9, 2016 [1 favorite]

When I was a kid I had a 2 liter bottle of 'muriatic acid' (HCl, maybe ~10N, as I recall), for use in my various plating experiments, among others, and one day I decided, for some unknown reason, to put a rubber cork in the bottle and screw the plastic cap down on top of that.

Within about two weeks, but between one day and the next, every piece of metal in the basement had a patina of rust or other corrosion on it; the acid had eaten the cork which fell into the bottle, leaving the vapors free to escape into the air.

Not that many people would have such hanging around their house, though -- that is, unless they were stripping the mortar off of recycled bricks, maybe glass bricks in this case, I might guess.
posted by jamjam at 5:53 PM on April 9, 2016

Jamjam, my father in law used muriatic acid ad a drain cleaner, Drano-like.
posted by SemiSalt at 5:57 PM on April 9, 2016

Since "muriatic" acid is used to remove cement lime mortar when cleaning brick, I wonder if there was some sort of "lime remover" for hard water stains involved.
posted by rudd135 at 7:00 PM on April 9, 2016

I used to work for a forensic engineering company. Water losses are a huge thing. We called it Kramer's Law after the old bastard who worked there for a million years and handled these things.

Kramer's Law states that anything water related that can fail, will fail at the highest point in the house and when the least people are around. I have seen millions of dollars of loss on a single property several times and it always follows Kramer's Law.

I have spent years chasing this shit down. I know the answer.

It's the cleaning things under the sink. I have seen so many rusted bullshit "stainless" connections. And everything else under there. They all get the treatment. Everything gets rusted or patina or whatnot.

I know this because I was sick of seeing it all the time and had to prove it to other people, so I bought a bunch of stainless toilet connections, the braid ones, and I set them in a closet and every two weeks I sprayed them once with whatever cleaner. Once. They were the most popular cleaners. Four setups, the four most popular cleaners.

And in the end it took like 6 months for STAINLESS STEEL to rust out and be leaky.

I think whoever is making those stainless steel fittings is lying. And I know so because we had a metallurgy lab too.
posted by sanka at 7:38 PM on April 9, 2016 [8 favorites]

The first thing I thought was Chinese Drywall. Used heavily in new construction from the late nineties through around 200o. Lots of it in Florida.
posted by Ruthless Bunny at 7:48 PM on April 9, 2016

It does sound like muriatic acid kind of thing going on. I've used the stuff to etch metal and seen the vapors alone corrode nearby metals in a matter of hours. Also, the various chemicals/cleaners used in bathroom cleaning and moisture will do a number to just about anything. I've also wondered if the combination of hot water, hard water, and maybe even some kind of galvanic action might be a factor in some sort of corrosion situations I've seen in bathrooms.
posted by 2N2222 at 10:41 PM on April 9, 2016

Sanka, your explanation ties in to my experience. Had a flexible hose under the sink burst, plumber could see it was all corroded even though it was fairly new. He gave the cleaning product explanation and it fits, the previous residents were super cleaning obsessed (I'd like to invite them over to clean sometime, place has never looked as good as when I moved in).

There's also corrosion on a few other stainless steel things.
posted by kitten magic at 12:18 AM on April 10, 2016

The Chinese drywall is an interesting angle, and fits the timeline in which the condo was built, but based on the description of how copper corrodes in that situation I don't think the glove fits. Definitely leaning towards cleaning products now. Thanks for all the answers.
posted by hafehd at 1:02 PM on April 10, 2016

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