Page 336 - Construction Waterproofing Handbook

7.4 CHAPTER SEVEN
TABLE 7.2 Properties of Masonry, Mortar, and Stucco Admixtures

Advantages Disadvantages
Simple installation No movement capabilities
Above- and below-grade installations Can stain or damage substrate
Becomes integral part of substrate Not completely waterproof

mixing times recommended by the manufacturer should be monitored for complete dis-
persal throughout the paste. Water added to the paste must be measured properly so as not
to dilute the admixture’s capabilities and properties.
These materials are not waterproofing but water-repelling products. They will not func-
tion if cracking, settlement, or substrate movement occurs.

CAPILLARY AGENTS

Hydration of concrete or masonry materials leaves behind microscopic pores, fissures, and
cracks from water that is initially added to make the paste mixture. This hydration allows
in-place concrete and masonry materials to absorb moisture through these voids by capil-
lary action. Capillary admixtures prevent this natural action and limit moisture absorption
and water infiltration into a substrate.
Capillary admixtures are available in liquid or dry-powder form that is mixed into the
concrete paste, applied by the shake-on method, or rolled and sprayed in liquid form to fin-
ished concrete. Capillary admixtures react with the free lime and alkaline in a concrete
or masonry substrate to form microscopic crystalline growth in the capillaries left by
hydration.
A substrate should be totally damp, to ensure complete penetration of capillary admix-
tures and provide the filling of all voids. This crystalline growth fills the capillaries, result-
ing in a substrate impervious to further capillary action. This chemical reaction requires
moisture, either contained in a substrate or added if necessary.
As with other admixtures, these systems are not effective when cracks form in the sub-
strate. Nor are they capable of withstanding thermal, structural, or differential movement.
Capillary admixtures are further limited by their reliance on a chemical reaction necessary
to form an impervious substrate. This reaction varies greatly depending on the following:
● Moisture present
● Alkali and lime available
● Admixture penetration depth
● Number and size of voids present
● Cracks and fissures present in a substrate
In the imperfect world of construction field practices, it is unrealistic to depend on so
many variables to ensure the substrate watertightness that is essential to the building enve-
lope. (See Table 7.3.)