Ask A Scientist Chemistry Archive

name         Scott
status       other
age          40s

Question -   I have recently had a new tile kitchen floor cleaned in my 
home using Muriatic Acid. (That was the builders idea.)The next morning 
all of the stainless steel appliances were discolored, tarnished and rusty 
looking. Can anyone tell me the affect the Muriatic Acid fumes have caused 
with the metal in my kitchen and also what will the long term affects of 
the metal being exposed to the fumes be?

---------------------
 
Scott,
 
It's not likely that the stainless was permanently harmed. Just give it a good cleaning 
with a soft-scrub cleaner made for stainless steel.
 
Regards,
ProfHoff 856
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Muriatic acid is the "old name" for 30% hydrochloric acid. Usually it
isn't necessary or desirable to use it "full strength" to clean a tile floor
(It dissolves some of the carbonate minerals in the tile.). Usually "white"
vinegar is sufficient to clean the surface of tiles, especially inside a
house. And the vapors will discolor even "stainless steel" because the
vapors condense on the metal surface with moisture to make more hydorchloric
acid. Steel is covered by a thin layer of metal oxides. The hydrochloric
acid dissolves and/or etches this layer leaving a tarnished look. It may be
difficult to remove that discoloration. As far as the health effects -- the
vapors are so irritating that unless someone cannot escape -- they will
leave the area before serious damage to the lungs occurs.

Vince Calder
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Muriatic acid is just HydroChloric Acid in water, rather concentrated, 30% HCl, 70% H2O .
By "tile" I suppose you mean ceramic rather than linoleum?
Anyway, HCl evaporates a bit easier than water, and like water it soaks into pores 
and plastics and takes its sweet time evaporating back out.
Its favorite thing in life to do is tickle iron into rust.
It doesn't take much to convince iron to rust.

Stainless steel is mostly iron, with fair fractions of nickel and chromium to make an 
extremely thin skin
 of tough oxide which stops corrosion in easy cases.
With trace quantities of Hydrochloric acid vapors in the air, your kitchen is no longer 
an easy case.
Various grades of stainless steel will resist seawater and HCL fumes for varying lengths 
of time, from days to months.
It appears your stainless is not the most corrosion-resistant grade.

You need to:
  - stop accelerating the rust: get your stainless out of there and neutralize acids on 
  it, very soon.
  - neutralize acid stuck on/in your kitchen surfaces, floor strongly and cabinets 
  mildly.
  - clean up the stainless, which might go into a little time & labor  & looking for 
  the best way.
  - make a safe place to keep the cleaned stainless so the surface can age in dry air 
  with no cloride or acid fumes pushing it towards rust.

Your kitchen might lose most of its acid vapors in a day to a week, if it gets fresh 
air,
   and if there are no cracks or absorbents (wood?) where substantial quantities 
   (milliliters) of the liquid are hiding.
If there have been ammonia vapors around, that can make the acid slower to evaporate 
away. NH3 (vapor) + HCl (vapor) <-> NH4Cl (a solid).
Waiting might work, but it's much better to actively neutralize acids after use.
It's even considered traditional to do this right after any acid treatment in a 
vulnerable environment.
In your case this doesn't seem to have been done.

To make sure the floor no longer has any acid on or in it, you should mop it with an 
alkaline or buffering solution.
Baking soda  (sodium bicarbonate, NaHCO3) in water is safe and probably adequate for 
this.  "TSP" cleaner is more strongly alkaline (anti-acid).
I'd try 2 gallons water plus 2 cups baking soda and 1/4 cup TSP, put down and then 
picked up with a mop, but not rinsed til a week later.
(You might not want to put bare feet on it for that time.  Don't apply TSP solutions 
to finished wood. Dilute baking soda solutions are probably OK.
If it dries and leaves white streaks or cloudiness on the finish, I'm hoping it's just 
a little baking soda, and that a couple of water wipes will remove it for good.)
Since the acid air got around and maybe settled onto/into wood surfaces, I might wipe 
all the exposed cabinet surfaces with a dilute baking soda solution,
and keep a few tablespoons of the powder on small saucers in each cabinet for a week or 
more.
With this and the doors closed, your cabinet is now a "safe place", or at least safer 
than before.

Meanwhile you can attempt to salvage your stainless and keep it in a safer place for a 
while.
 I think it can be done without scratching and without leaving much visible evidence of 
 the rust.
First I'd try to pry off rust particles with copper-wool potscrubbers or brass brushes 
from hardware store,
soap & water with baking soda, perhaps non-abrasive polish pastes for stainless, or maybe
 even some oils (to be washed off later).
I'd follow that with brief full-strength applications of acidic rust-dissolvers like 
Naval Jelly or CLR,
with immediate copious hot-water rinsing, a baking soda solution dip, a final hot 
rinse,
and drying in an electric oven at about 250-350F (if the handles can take it).

If your stainless has really darkened, tarnished, that's a tougher problem and I know 
less about what to use for that.
Stainless usually looks blue or dark or burned or tarnished from an oxide film grown too 
thick, and looks better if that can be stripped off.
But it's difficult.
Maybe a polishing compound for stainless and chrome.
There are hot acids that do it, but most people wouldn't want to use them.
The talkers at  have polished some 
stainless.
Scotch-Brite plastic mesh abrasives on power tools, they've used.

Someone mentioned industrial electro-polishing (big hot acids plus electricity).
They warn never to use steel wool or similar, because it leaves embedded bits of iron 
that rust soon.

Bicycles at my workplace always rust fast, right thru the paint.  Stainless breaks out 
in a while, too.
We use lots of acids, but only in the sinks.  We presume we have similar traces of acid 
in our air.
Unfortunately it's a poorly enclosed industrial-style space and we can't imagine how to 
fix it.

Jim Swenson
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