There are two main reason why many garages begin to have serious structural problems within eight to ten years after they are built. The first is unfamiliarity by the designer with the use and operational characteristics of this kind of building. The second is lack of adequate drainage and waterproofing. The biggest single cause of parking deck deterioration is again the design- expansion joints that are designed improperly (usually of inadequate size) and put in the wrong places, control joints too far apart or in the wrong places with respect to the ramp system used, and as cited already inadequate (or nonexistent) drainage and waterproofing. Another confusing problem with parking structures is the large number of manufacturers who make materials that they claim will seal and waterproof. Our company has on file more than 30 different types of materials, all said by the manufacturers to work well on garage decks. Unfortunately, few of the products work well and some not at all. Products developed for waterproofing retaining walls and foundations do not necessarily work equally well on parking garage decks. There are several concepts being applied to waterproofing of parking garages. One, the first employs a tough, plastic type of membrane sprayed or troweled onto the slab in several different layers. The system may have one or more drawbacks. First, in our company's experience about half the jobs work out well while the other half do not. The second problem is that such a wearing surface has a tendency to wear out from traffic within a few years. Third, some products seem to deteriorate with long exposure to sunlight. Another waterproofing system is a membrane of sheet rubber or other type of material applied to the structural deck and then covered with a concrete topping slab which serves as the wearing surface. This system has not proved highly satisfactory in cases where water seeps through hairline cracks. There are many liquid slab sealers used as waterproofing agents. These do penetrate the slab somewhat and retard seepage of water directly into the slab. The fourth type of waterproofing process takes a different approach altogether. Several layers of a sticky mixture of latex rubber and asphalt are applied to the deck. It is topped with a wearing surface, usually some type of asphalt.