Muriatic acid is not always safe for concrete. Note that the
recommendation given is for diluting the acid and then washing it off
afterwards. Muriatic acid dissolves the calcium carbonate in concrete,
in effect etching the surface somewhat.
Lowe's recommends using a cleaner specially formulated for cleaning
concrete, I presume, to avoid too much etching. (Note that some
driveway cleaning products may be formulated more for removing oil
than for removing tannins.)
** Effect of concentrated muriatic acid:
Here are some comments on what happened when muriatic acid was used to
clean car parts and some got on the concrete flooring:
"About a month ago my very nice driveway started showing odd spots and
strips of what looks like what an acid might do. There has been some
vandilism in the area, and I am wondering if this new appearance on
the driveway could be from acid?"
"Acid is pretty easy to tell, the acid will eat the top layer off the
concrete. This will expose the sand in the concrete. It looks like it
was worn away in spots. If the "cream" is still on the top, it was not
Being in the swimming pool industry for 12 year, I have seen this too
many times. I usually see it in pictures, with a letter from a lawyer
telling me one of the guys that works for me ruined something... glad
to be out of that business."
"I TRIED MURATIC ACID TO REMOVE A CYLINDER ONCE, GOT SOME ON MY GARAGE
FLOOR, IT DIDN'T STAIN, IT ATE AWAY THIN COAT OFF THE TOP OF THE
** Lowe's advice on removing driveway stains:
(The cat litter recommendation should be for oil rather than tannins -
unless the tannins were part of spilled stain for wood.)
"More on Concrete Stains
The tannins found in tree sap, leaves and nut husks have been used as
a natural stain for wood and yarn for years. They can also stain
concrete. Oil and grease are common culprits.
Each type of stain has its own challenges. Much of your success will
depend on the severity of the stain. You may have to clean the area
several times to get results. It also helps to act as quickly as
possible after the stain occurs.
Clean large amounts of a fresh spill by covering the area with cat
litter. The litter will absorb most of the material. Dispose of the
used litter properly.
To remove remaining material or if the stain is old, it is advisable
to always look for a cleaner specially formulated for cleaning
concrete. If you are in a pinch, try one of these:
Household bleach - Dilute as the directions indicate for cleaning. Let
the solution sit on the stained area for several minutes, then scrub
Laundry or dishwashing detergent - Sprinkle dry detergent over the
area. Let it sit for a few minutes and then scrub with hot water.
Tri-sodium phosphate (TSP) - Dilute one cup in one gallon of hot
water. Pour it on the area and let it sit for 15-20 minutes. Scrub
with a stiff brush. Rinse off with hose and repeat if needed. TSP is
also available in a phosphate-free version.
Always wear eye and skin protection when using cleaning chemicals.
Muriatic acid is not a stain remover or cleaner. The acid actually
etches away the concrete itself, and sometimes the stain as well. You
will need to scrub and rinse this chemical also. Follow the directions
carefully and WEAR EYE AND SKIN PROTECTION. Since you will be removing
the actual concrete, use muriatic acid only if you seal the driveway
with masonry sealer afterwards. Remember that you will be altering the
level of the surface if you remove a lot of material.
To avoid damaging concrete:
If you use a pressure washer, make sure you have the right nozzle. A
jet that is too concentrated can damage concrete.
Use a nylon scrub brush, not wire."