Design professionals, contractors, municipal authorities and even home owners throughout North America routinely come up with the same question about paving stones, "How do you clean and maintain them?" In order to answer that question, you must first identity what needs to be cleaned off of the pavement and what you can do to maintain their looks as well as their performance.

Efflorescence is a phenomenon that occasionally occurs on concrete and masonry products, it is a soluble salt that forms on the surface of these products. Appearing as a whitish staining on concrete and clay paving stones as well as other concrete products and aside from being unsightly, efflorescence does nothing to compromise the integrity of these products. There are two types of efflorescence; primary efflorescence, which is present after manufacture and visible before the paving stones are installed, and secondary efflorescence which is not immediately visible, but occurs after the paving stones are installed.

These two sets of pavers exhibit efflorescence which is a soluble salt that often forms on the surface of concrete and masonry products. Though the whitish residue is unsightly, it does nothing to compromise the integrity of the paving stones. To dissolve efflorescence from installed pavers, use a cleaner made of dilutions of hydrochloric or sulphuric acid combined with a surfactant.

Manufacturers have learned that they can control efflorescence by insuring that their raw materials are pure and contain no soluble salts and by using high quality admixtures specifically designed to control efflorescence. When specifying or purchasing paving stones for a project, it would be prudent to insure that your manufacturer is using a high quality admixture to control efflorescence.

If efflorescence should appear on the surface of your paving stones, many times it will dissipate by exposure to weather and normal traffic. If you have stubborn efflorescence stains or immediately need to remove the stains, there are some high quality efflorescence removers available. These cleaners typically are made of dilutions of hydrochloric or sulphuric acid combined with a surfactant (detergent) to dissolve the efflorescence as well as clean the surface of the pavement. With any acid type cleaner, caution should be taken to insure that the paving stones are thoroughly saturated with water first so that the cleaner stays on the surface and is not drawn into the surface of the paving stone. If care is not taken when using this type of cleaner, the actual paving stones can become permanently damaged. An additional concern that must be considered is the issue of where the acid cleaner rinse water is draining. It must be thoroughly washed down and directed away from plant material or if it does drain in the area of plant material it must be diluted with copious amounts of water to neutralize the acid.

Rust stains occasionally occur on paving stones; sometimes-metal furnishings, an automobile radiator leak or any contact with a rusted metal surface. Cleaning these stains is possible by again using a high quality rust stain remover, which is formulated for paving stone usage. These cleaners are typically made of a phosphoric acid or blend, which includes phosphoric acid. This acid cleaner requires the same cautions regarding the saturation of the paving stones with water and proper attention to the drainage of the rinse water.

Stains from paint and oil can be cleaned with an active solvent that emulsifies the stains and allows them to be wiped off.

Stains from tires, paints, and tar can be cleaned with available high quality cleaners. These cleaners contain an active solvent that emulsifies the stains and allows them to be wiped off.

Normal dirt, foods, drinks, oils and everyday stains can be removed with high quality cleaners specifically formulated for paving stones. These cleaner are detergents that cut the stains and allow them to be washed away. Something important to remember, if you immediately address a paving stone stain, you have a better chance to successfully remove it, but if you allow it to set and penetrate the paving stones, your chances of a totally successful removal are reduced or possibly eliminated.

The option of sealing paving stones to help protect them from staining has become more popular in the past 10 years. Some people seal with a solvent based sealer, which darkens and intensifies the color of their paving stones, while others seal with a water-based sealer, which basically maintains the original look of the paving stone. Whether you seal your paving stones or not is a personal choice, but one must understand that sealing does not guarantee the stains will not penetrate the sealer, rather it slows their penetration and allows more time to permit the cleaning of your paving stones.

Rust stains typically result from metal furnishings or automobile radiator leaks. The best way to clean them is with a phosphoric acid or blend, which includes phosphoric acid.

The question, "When should one seal their paving stones," if often asked and with good reason. If you seal your paving stones first and efflorescence appears, the efflorescence will become trapped between you sealer and the paving stones. Trapping the efflorescence between the sealer and the paving stones prevents the normal removal of the efflorescence because it is shielded from the cleaner. If this was to happen the sealer would have to be stripped and then the cleaning would have to be attempted. This is not always a successful situation; therefore normally the manufacturers would prescribe an amount of time to wait before sealing with their product. Some manufacturers recommend waiting 90 days before sealing, because this seems to be an accepted amount of time to believe that if efflorescence has not appeared within the 90 days, chances are that it will not appear. There are some sealers that are considered permeable and that will allow efflorescence to form on the surface of the sealer. If sealing is your option, it would be smart to contact the sealer manufacturer and find out their recommended application time is and also ask if their sealer is permeable to allow efflorescence to form on the sealers surface.

Everything that I have previously discussed has related to keeping your pavement looking good, but there can be an added benefit of stabilizing your joint sand by utilizing a water-based sealer. Joint sand is critical to maintaining the performance of your paving stone installation. If joint sand is eroded, the structural integrity of the pavement can be compromised. By flooding the paving stone surface and sand joints (the paving stones and joint sand must be dry before application) with a high quality water based sealer and squeegee the excess sealer off the paving stone surfaces, the sealer penetrates the sand joint, stabilizes the sand and also seals the surface of the paving stones. Another method of stabilizing your joint sand is to install a dry joint sand that is blended with a material that hardens once exposed to water.

Sealing a paver with a solvent based sealer will darken and intensify the stone's color while a water-based sealer will basically maintain the original look of the paving stone.

There are many good quality products available to remove stains from your paving stones and to help maintain them, but just keeping them clean on a regular basis can make your overall job much easier. On larger scale projects I have found that a hot water, pressure washer with a soap aspirator can do a great job. If you mix a simple solution of Tide and have a pressure washer with water at 215 degrees, pressure between 2500 & 3000 psi and a high volume water pump, you can clean grease, ice cream, chocolate, milk, candy, soft drinks, etc. and yes even gum. Once you melt and wash away the dirty stain, the Tide keeps it from sticking to anything so that you can rinse it away cleanly. Hot water and soap does bring us back to the basics of cleaning and if you do find a stain that you just can't deal with, take advantage of the flexibility of interlocking paving stones, by removing and replacing those unsightly stones (something no other form of pavement allows). LCM

Photos provided courtesy of Addiment Incorporated. For more information call 800-458-3090 or visit them online at www.addiment.com.