Despite its effectiveness muriatic acid should be used on concrete stains only if you ve tried gentler alternatives to no avail.
Cleaning oil from concrete with muriatic acid.
Make sure the detergent you use is ammonia free.
Muriatic acid is diluted hydrochloric acid and is a very potent chemical.
The acid works well on concrete and on many masonry projects because it neutralizes alkalinity.
While some stains can be rinsed away with a pressure washer tougher stains such as rust require an acid based cleaner like muriatic acid.
It cleans concrete by removing the topmost layer of your driveway.
Scrub the gray stain with a solution of 1 cup liquid chlorine bleach 1 cup powdered laundry detergent and 1 gallon of very hot water.
Use it only as a last resort to clean stains.
Before washing your driveway with muriatic acid try a degreaser on oil stains and a solution of one part bleach to three parts water on mold and mildew.