Why are water repellents needed?

Water has long been recognized as the most destructive natural element to masonry structures. Many desirable characteristics of masonry such as cost effectiveness, low maintenance and durability can be compromised when masonry is left unprotected.

Unprotected masonry commonly absorbs water. A 2 ft. by 2 ft section of this wall is treated with a water repellent. The area is easily identified when water is applied. It repels the water and remains dry. Notice how the untreated area darkens as the water is absorbed.


The following series of photos depict some of the more common water related problems:




When water penetrates masonry and freezes, it expands. If the expansion is restricted due to saturation, a force capable of creating cracking or the flaking and chipping known as spalling is generated.







In addition to being an aesthetic issue the integrity of the structure is also affected. If this is left unchecked the problem will only get worse.







Efflorescence is caused by water as it migrates through masonry dissolving soluble salts. As the water evaporates, the salts recrystallize and are deposited on the surface leaving the white powdery residue that appears to ooze out of the masonry. Eventually all that is left is a weakened silica sponge.





Like efflorescence, calcium carbonate stains occur when water migrates to the surface carrying soluble calcium hydroxide that is deposited as the water evaporates.

These stains are often referred to as lime run and appear as hard encrusted streaks.






It is much easier for water to transport the dissolved calcium hydroxide through structural openings. This is the reason that staining is most likely to appear around joints, cracks and weep holes.




Mold spores constantly circulate in both indoor and outdoor air and will prosper on any surface that provides moisture and a source of food. It appears as a wooly growth in damp stagnant areas. Not only is it a health concern but, left untouched, it will actually break down masonry surfaces.

Since mold is dependent upon moisture, the best way to control it’s growth is to control the moisture.




Another cause of deterioration are the pollutants in the atmosphere that combine with moisture to form acid rain.

As it penetrates into masonry it depletes the cementitious elements and corrodes reinforcing steel. This weakens the structure and can result in the development of cracks and surface spalling.

Especially vulnerable are acid soluble building materials like marble and limestone. The worn facades of architectural monuments and historical buildings, for instance, are evidence of the damaging effects of air pollution and acid rain.




Water repellents are one of many structural design elements that make up the belt and suspender system which provides a watertight building envelope.

Design elements such as weep holes, cavity wall construction and proper drainage are reactive in that they deal with water once it has passed through the masonry. Water repellents, joint sealants and flashing, on the other hand, are proactive in that they stop the water at its source before it has a chance to enter the masonry.