Phosphoric-Acid Cleaners

• When using phosphoric acid and cleaners containing the acid, dilute the substance with warm to hot tap water in a ratio of 1 part acid to 10 parts water. Wear rubber gloves, a nose mask and safety goggles to keep the phosphoric-acid solution off your skin and out of your eyes. The nose mask keeps the smell of the solution out of your lungs. Stir the solution thoroughly before using it and work in a well-ventilated area to keep the acid's smell from affecting others that may be in or close to the room or area.
  
  

Using the Acid

• Wipe the surface containing the dried grout with a soft cloth or rag to remove any loose dust and dirt. Use a scrub brush or shop towel to apply the phosphoric-acid solution to the grout. Let the solution stand for five to 15 minutes, then scrub the surface clean. Repeat until the grout is debris free.
  
  

Follow-Up

• Apply an alkaline cleanser with a pH factor between 7 and 9 to neutralize the phosphoric acid solution and clean any residue from the tile surface. Alkaline cleansers are available at hardware, home-improvement and chemical-supply stores, as well as online chemical and hardware outlets. Failure to neutralize and clean the surface can lead to the acid solution damaging and deteriorating the grout and tile or other surface.
  
  

Availability

• As with alkaline cleansers, phosphoric acid and solutions containing the chemical are available at hardware, home-improvement and chemical-supply stores. The chemicals come in a variety of package sizes including liter, gallon and drum. Phosphoric acid and cleaners containing the chemical vary in price. Follow any and all directions and recommendations on the chemical's container, as well as storage suggestions.