The architect is specifying the product DRY-BLOCK by gcp applied technologies as an integral waterproofing admix to be added to the block that are to be covered with a direct applied stucco. Is this what the industry would recommend?
The masonry industry and the stucco manufactures in Florida clearly DO NOT recommend the use of an integral waterproofing agent in masonry to be covered with direct applied stucco. This is not specific to the DRY-BLOCK product but applies to ANY integral waterproofing agent added to the block during the manufacturing process.
The reason is simple - integral waterproofing agents negatively effect the bond between the block unit and the stucco coating. This bond is one of the most important aspects direct applied stucco coatings. The problem is that good stucco bond depends on absorption of cement and water, out of the stucco, into the pores of the block. The integral waterproofing agents are an excellent product for preventing exactly this type of water movement.
Integral waterproofing in the masonry is highly recommended for single-wythe masonry walls which are not covered with direct applied stucco. They would also be appropriate for masonry covered with stucco attached to lath that is then mechanically attached to the block.
In the case of direct applied stucco, the stucco itself is the primary waterproofing barrier protecting the wall. Stucco has proven itself an effective waterproofing barrier by both experience and testing.
Jerry Painter, FASTM
Don Beers, PE, GC
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