Q.: The stalls in our company parking lot have become unsightly because of oil stains that have accumulated over many years. Is there an effective way to remove the stains?
A. One method has been described in Problem Clinic in the April 1982 issue, page 386.
More recently, similar methods have been studied by the National Ready Mixed Concrete Association and these have been described in the January 1984 issue of the Association's Promotion Pointers.The study investigated the use of three agents:
- a solution of 5 percent sodium hydroxide to be used with ground limestone
- granular trisodium phosphate crystals to which hot water was added
- a proprietary driveway cleaner and degreaser containing sodium metasilicate and petroleum distillate
Tests were conducted on a pavement where oil spills had been accumulating for 20 years. A heavily stained area (see first photo) was selected and scraped with a putty knife to remove accumulated grease and dirt. The area was then marked off into three parts so that one agent could be tried on each part and compared with the other agents.The sodium hydroxide solution used can be made from sodium hydroxide pellets or flakes at the rate of 0.5 pound per 10 pounds of water (or 6.5 ounces per gallon).
The solution was mixed with enough ground limestone to make a stiff paste. This paste was then spread over the stain with a putty knife and allowed to dry completely. It was subsequently brushed off.The trisodium phosphate crystals were sprinkled on the stain until the stain was completely hidden. Hot water was added and the area was scrubbed with a stiff brush. After 30 minutes the area was thoroughly rinsed.The commercial driveway cleaner and degreaser was scrubbed into the stained area and then the area was thoroughly rinsed.
The second photo shows the results, all of which were adjudged to be good. The paste of sodium hydroxide and ground limestone was the most effective but was also the most time-consuming, both in the time required to apply it and in the time needed for the drying process, which takes at least 24 hours. The trisodium phosphate and the driveway cleaner have the advantages of being easy to obtain, and fairly easy to apply, yet productive of good results. Sodium hydroxide can be purchased from chemical supply houses or, in the form of lye (stocked for cleaning household drains), from a hardware store. Ground limestone can be obtained from various sources such as materials yards, limestone quarries, garden and lawn supply centers, or hardware stores. Hardware stores are also the source of both trisodium phosphate and the particular commercial cleaner that was used (which contains sodium metasilicate and petroleum distillate).