Page 334 - Construction Waterproofing Handbook

7.2 CHAPTER SEVEN
Only controlled conditions of perfectly portioning, mixing, placing, and curing the con-
crete slurry will produce materials with minimum voids and absorption. Since field con-
struction is never completed perfectly, however, concrete and masonry products often leak
through the voids and cracks formed by the curing process.
The purpose of waterproofing admixtures is to provide complete hydration, which in
turn promotes internal curing. This allows a reduction in shrinkage, providing a denser,
higher-strength, and more water-resistant product by reducing the water absorption rates
of a concrete or masonry material.
Admixtures available for concrete and masonry products that impart waterproofing or
water-repelling characteristics include:
● Dry shake
● Concrete admixtures
● Masonry admixtures
● Stucco admixtures
● Agents
● Polymer concrete

DRY SHAKE

The dry shake, power troweled, or shake-on methods use materials similar to cementitious
membranes for below- and above-grade waterproofing. The difference is that unlike materi-
als for cementitious membranes, dry-shake admixture is applied during initial concrete fin-
ishing and curing (green concrete) rather than after curing. Shake-on admixtures consist of a
cementitious base with proprietary chemicals that provide water-repellent properties.
These products are broadcast in powder form at 4–1 lb/ft of substrate area before ini-
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tial concrete is set. Power troweling then activates proprietary chemicals with the moisture
present in concrete.
With this method, the cementitious admixture becomes an integral part of a concrete
substrate. These products do not merely add water repellency; they waterproof concrete
against water-head pressure. They are effective admixtures, used when waterproofing of
concrete substrates is required. These admixtures add compression strength to concrete
substrates, and abrasion resistance to withstand heavy traffic and wear. As with all cemen-
titious systems, these products do not withstand cracking or movement in substrates by
structural, thermal movement, or differential movement. (See Table 7.1.)

DRY-SHAKE APPLICATION

Dry shake-on surface preparation requires only that concrete be in its initial setting stage,
before power troweling. Areas being placed or finished should be no larger than a work crew
can adequately cover by broadcasting material during this precured stage. Should concrete
begin setting and curing, this method becomes ineffective for substrate waterproofing.