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using muriatic acid inside house?

toolinaround's picture

Hey all,

     My gal has found a great process to use on floors.  The question is....there is a slab floor in the house, and the process includes washing the floor w/muriatic acid...Any ideas?  Use lots of to prevent wicking up drywall?  Can you use a shop vac or is that inviting some sort of death and destruction?  I REALLY hate to sound like an idiot, but have never used the stuff...thanks for any/all thoughts.   Beck

Re-Home Solutions Inc.

Re-Home Solutions Inc.

(post #62662, reply #1 of 19)

NO WAY would I ever use Muriatic acid in a house.  I use it to clean off algae off the outboard motor of my boat.  Just getting one whiff of the fumes of that stuff makes me gag and almost vomit.  It just destroy's the algae, but I now have learned to wear a respirator when using the stuff.  The odor is VERY strong and should NOT be used indoors.

Dark Magneto

(post #62662, reply #2 of 19)

I have used it indoors with caution to clean grout. I always wear a respirator and heavy rubber gloves and have plenty of water and baking soda nearby to neutralize any residual acid.

To give an example of why one needs to respect the strength of this acid, the fumes in one instance corroded the silver backing around the edges of the bathroom mirror.

Don't use it if you are lacking in confidence in your ability to do so safely.


(post #62662, reply #3 of 19)

Muriatic acid is is just hydrochloric acid. It's actually one of the safer acids to deal with. The main hazard is simply that, in "industrial strength", it's highly concentrated.

With any strong acid it's important to remember to never add water to acid -- always add acid slowly to the container of water instead. This prevents a strong exothermal (heat-producing) reaction that can spatter the acid all over everything.

A second rule for any acid (and also a number of other chemicals like bleach and ammonia) is to never mix two chemicals together unless you're quite sure it's safe to do so. You could end up producing a cloud of poisonous gas if you're not careful.

You should use goggles, rubber gloves, long sleeve shirt, and long pants when dealing with the concentrated stuff. Expect it to eat holes in anything it spatters onto (though the holes may not appear until the article is laundered). Generally you should dilute it 10:1 or so when etching concrete.

Ventillation is critical with any acid. The acidic fumes can damage metal surfaces in the room and can also damage your lungs. In addition, muriatic acid produces a fair amount of poisonous chlorine gas as it degrades or reacts with concrete.

The good news is that muriatic acid leaves no residue. You need to rinse away the dissolved calcium from the concrete, of course, and also rinse away as much of the left-over muratic acid as possible, but any remainder will react with the concrete and become relatvely harmless calcium chloride. Just maintain good ventillation in the area for 12-24 hours -- until the "bleach" smell disappears.

In terms of water wicking up the drywall, the drywall should not rest on the slab to begin with -- it should be held at least a half-inch off. If not it would be a good idea to cut off the bottom half-inch or inch of the drywall.

It should be fine to use a shop vac to vacuum up the residue. Use it in wet mode, and pre-fill the vac with a half-gallon or so of water to help absorb any gasseous acid. Make sure the vac exhaust (which may contain acid mist) is not blowing at anyone or anything. (It might be good to put a hose on the exhaust and direct it out a window.)

Rinse the vac well after using it this way. After rinsing it may be a good idea to feed the vacuum a box of baking soda or a half-pound of garden lime or some such to help neutralize any acid in the unit.

For yourself, take a shower ASAP after using the acid, and wash (or pre-rinse) the clothes you used separately.

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

(post #62662, reply #4 of 19)

Muriatic is the same as hydrochloric. It has the potential for for creating life threatening conditions particularly in enclosed areas. It can off gas hydrogen and a spark such as from a motor (shop-vac) can cause a Hindenberg like explosion. You are better off not using the stuff, phosphoric acid is a safer product for this use. Visit the following site.

Beat it to fit Paint it to match

Beat it to fit / Paint it to match

(post #62662, reply #5 of 19)

HCl is no more likely to produce hydrogen gas than any other acid.

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

(post #62662, reply #7 of 19)

My chemistry teacher would be surprised that I even knew what muriatic was. It does take a chemical reaction for hydrogen gas to form in a significant amount. My understanding is that when combined with a neutralizer such as lime, these conditions can occur. Chlorine gas can also be generated. Certainly something to be aware of in an enclosed space. I think exposure to the fumes of the acid is reason enough to stay away, not to mention what it does to your clothes, tools and perhaps anything metal that is nearby. The risk of explosion is minimal. It's never a bad idea to err on the side of safety and to carefully consider all the possible scenarios. Acid can be a serious chemical so I recommend treating it seriously. Slathering up a basement with it could have some dire consequences.

Beat it to fit / Paint it to match

Beat it to fit / Paint it to match

(post #62662, reply #8 of 19)

nasty stuff indeed.

I had a jug of it for cleaning a slate hearth I made. I mindlessly just put it under the kitchen sink with all the other stuff for cleaning. Twoo weeks later ALL of the wifes pots and pans and cookies sheets in the adjacent cabinetry were DESTROYED..

I thought she was gonna kill me...I later dumped the stuff, once I realized what caused the hoopla..


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(post #62662, reply #9 of 19)

Gee, that musta got you squirmin!!!!

A few of the local H ware stores around here won't stock it any more cause it was leaking vapor through the lid and wrecking the paint cans and a bunch of other stuff.

No oatmeal raisan cookies for you!!!


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(post #62662, reply #12 of 19)

I had a co-op job in highschool as a handiman. The local developer I worked for had a five gallon jug of concentrated hydrochloric acid he wanted to throw away. Told me to dump it in a vacant lot or the sewage treatment pond at the hotel he owned. I talked to my dad, a chem engineer, and ended up digging a hole and filling the hole with crushed limestone from a parking lot and pouring the acid over it. Had to dump a little and run upwind to get out of the fumes. Right, it is nasty stuff.

(post #62662, reply #10 of 19)

When an acid is combined with a base, what is produced is water and "salt" (though not necessarily sodium chloride). The H in HCl combines with the hydroxide in the lyme to produce water. The Cl in HCl combines with the calcium (and other related minerals) to produce calcium chloride, et al.

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

(post #62662, reply #11 of 19)

And not to mention all of the residual corosion that will take place in the house from the fumes...

Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming

WOW!!!   What a Ride!

"Some days it's just not worth chewing through the restraints"

(post #62662, reply #14 of 19)

Right. If you want hydrogen, you need metal, I believe, [see edit below] like in a car battery where the sulphuric reacts with the lead and off gases hydrogen. Or, do the cheap bomb thing and put drain cleaner in a plastic pop bottle with little pellets of aluminum foil. Exothermic rxn melts the pop bottle and the gas blows it up like a balloon. Don't try this at home.

Oh, aboout the Hindenburg. Latest (?) theory is that it wasn't so much the "exploding" (burning) hydrogen as it was the burning of the thermite-like coating on the dirigible. Thermite is made from aluminum and iron oxide (? not real sure about it's composition) and burns at very high temperatures. Used to be used to weld train rails. It burns a lot like magnesium.


EDIT: I think I'm wrong about hydrogen gas--I think the guy who said be careful may be right--if the chlorine in the HCl reacts with the calcium in the concrete to give you calcium chloride, the hydrogen in the HCl has to go somewhere or bond to something and I think it's just liberated as gas. Haven't had chemistry since highschool over 30 years ago, so I may be wrong...but I don't think so.

Edited 9/18/2004 7:40 am ET by Danno

(post #62662, reply #15 of 19)


The calcium (and magnesium) in concrete, mortar, etc is in the form of calcium (or Mg) carbonate, which is relatively insoluble.  Reaction with hydrochloric acid produces calcium chloride, which dissolves very easily in water.  The remaining hydrogen then reacts with the carbonate portion to form water and carbon dioxide. This is what makes the "fizz" when you pour it on the floor.

       CaCO3  + 2HCl = CaCl2  + H2O + CO

You are right that it generally requires a metal in elemental form to react with an acid to produce free hydrogen

Doc - The Old Cynic

(post #62662, reply #16 of 19)

Hey all,,,Thanks SOOO much for all the responses.  Been out of town for a few days so I didn't get a chance to respond to all.  I will take everything into consideration, especially researching other possibilties. You all are great....and why I spend too much time on the computer!  Thanks.. Beck

Re-Home Solutions Inc.

Re-Home Solutions Inc.

(post #62662, reply #18 of 19)

Now that everyione has told you why not to use it, let me suggest a more positive solution.

The reason the muriatic works to clean is that it is an acid and the stains on floor sre usually like most dirt - bases. Th eacid and base neutralise each other to relese the bond.

There are other safer acids, like white vinegar, that are sfe to use tho.


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(post #62662, reply #17 of 19)

Thanks for the info.

(post #62662, reply #19 of 19)

When prepping surfaces for paint, a mixture of TSP and Chlorox is often used for cleaning. If a painter mixed residual amounts of these substances inadvertently with the muriatic, I've been told it can release noxious gas. This may be concentrated in a shop-vac or sump pump drain particularly is a person was unaware a danger may exist. The fumes of even heavily diluted muriatic find their way to metal and can start a chemical reaction that is hard to stop. Drain pipes, lally columns, furnaces and so on are affected. Why use it when there are phosphoric acid masonry cleaners that work well and are safer to use.

Beat it to fit / Paint it to match

Beat it to fit / Paint it to match

(post #62662, reply #6 of 19)

There are some "safety" etching chemicals.

I first one says that it is a concentrated organic food grade acid.

I suspect acetic.

. William the Geezer, the sequel to Billy the Kid - Shoe

(post #62662, reply #13 of 19)

Muriatic acid, in and of itself, doesn't say much. We all have this acid, fairly concentrated at .6 mol, in our stomachs. Laboratory grade acid is much more an issue than the stuff they sell for lowering the PH of pools.

Diluted and used in a well ventilated environment for a limited time and not too often I wouldn't expect too many problems. No big deal. Using a wet/dry vacuum should be OK. I would empty the tank promptly, rinse well and run the unit in clear air for a bit to get any chlorine out of the motor but I have sucked up worse.

You could neutralize the acid but I would just flood rinse the floor a couple of times after the acid. Pour on the water, swish with a broom and mop or use a wet vacuum.

Even diluted I would wear rubber boots, gloves and splash proof goggles. I have seen the much stronger stuff used to mix the solution clean masonry get in eyes and on skin. Sometimes used straight. It stings and produced a little redness but as long as it is rinsed off in a timely manner no long term issues. Probably didn't do us any favors. Ate holes in out clothes. Do not wear contacts as these can hold the acid against exactly where you don't want it to be.

Use the proper protection and keep a supply of water handy in case it gets away from you. A pressurized hose with a closing nozzle would by my choice. If the undiluted stuff gets in your eye you don't want to have to run around the corner to turn the water on and run back to get to the flow.

A bucket of sodium bicarbonate, baking soda, dissolved in water will rapidly neutralize most acids. Have this on hand if you are handling more concentrated solutions. With the swimming pool stuff I probably wouldn't bother. A long rinse with flowing water would be my choice.

How to keep it from soaking into the drywall? Do what floor finishers do. Do the middle of the floor by flooding but use an unsaturated mop around the edges. Work edge to middle with the mop more dry at the perimeter. It is not hard to do once you get the hang of it.