Figure 10 shows the relationship between cover thickness and the amount of deterioration of the steel as a function of time. It is recommended that a minimum cover of 58 mm be placed over the top steel and that a minimum of 20 mm cover the bottom bars. In addition to an adequate cover of concrete there are several artificial barriers to prevent the ingress of or greatly reduce moisture in concrete. Sealers applied to the surface reduce the permeability of concrete. There are various types of sealers, as outlined in Table 1.
Sealers have the great advantage of being easy to apply and low in cost.
On the other hand, they lack the ability to bridge cracks and they tend to wear off. There are great differences among sealers with respect to various properties presumed to be relevant in garage applications, such as water absorption, fluidity, and stability. Unfortunately, standards are not yet available and selection must be based on past field performance. Made of various materials, such as polyurethane, PVC, neoprene, and epoxy, they are supplied as either preformed sheets or emulsions. In most cases, to protect the integrity of the membrane from traffic, another course, called the wearing course, is required.