This is the case in many concrete structures that have been repaired. Examples are concrete bridge decks or parking garage slabs saturated with deicer chemicals, and exposed concrete frames of high-rises built using calcium chloride as an accelerator. Before applying a protective coating to parking garages and similar concrete structures, consider how the method of concrete surface preparation may affect the internal moisture content. Wet sandblasting, hydrodemolition, and other methods that use a lot of water soak the structure during the repair process. This addition moisture must be considered when selecting and installing protective coatings, and in predicting distress that may occur beneath the coating Avoid encapsulating moisture-laden concrete .
Encapsulation occurs when a protective system completely seals the surfaces of a concrete member.
A typical example is a concrete balcony slab on a high-rise apartment building with the top surface covered by a protective waterproofing coating and a nonbreathable paint applied to the underside. This situation also occurs in concrete parking garages when extensive concrete repairs are protected with a coating on top of the slab and the slab underside is painted to improve appearance or lighting efficiency. In these situations, slab moisture has nowhere to go. Most available water proofing coatings have poor moisture vapor transmission characteristics. Paints may allow greater vapor transmission.