Page 139 - Construction Waterproofing Handbook

3.28 CHAPTER THREE
With all applications, the second material coat should be applied within 24 hours after
applying the first coat. Using these application rates, under normal conditions, a 50-pound
2
2
2
bag of coating will cover approximately 150 ft (1 lb/yd , first coat; 2 lb/yd , second coat).
The finish thickness of this application is approximately 8 in.
1
Trying to achieve this thickness in one application, or adding excessive material thick-
ness in one application, should not be attempted. Improper bonding will result, and mate-
rial can become loose and spall. To eliminate mortar joint shadowing on a masonry wall
being visible through the coating, a light trowel coat application should be applied first,
followed by a regular trowel application.
The cementitious coating beginning to roll or pull off a substrate is usually indicative
of the substrate being too dry; redampening with clean water before proceeding is neces-
sary. Mix proportions must be kept constant and uniform, or uneven coloring or shadow-
ing of the substrate will occur.
After cementitious coatings are applied they should be cured according to the manu-
facturer’s recommendations. Typically, this requires keeping areas damp for 1–3 days. In
extremely hot weather, more frequent and longer cure times are necessary to prevent
cracking of the coating. The water cure should not be done too soon after application, as
it may ruin or harm the coating finish. Chemical curing agents should not be used or added
to the mix unless specifically approved by the coating manufacturer.
Typically, primers are not required for cementitious coating applications, but bonding
agents are usually added during mixing. In some cases, if substrates are especially smooth
or previous coatings have been removed, a direct application of the bonding agent to sub-
strate surfaces is used as a primer. If there is any question regarding bonding strength, sam-
ples should first be applied both with and without a bonding agent and tested before
proceeding with the complete application.
Cementitious coatings should not be applied in areas where thermal, structural, or
differential movement will occur. Coatings will crack and fail if applied over sealant in
control or expansion joints. Cementitious-based products should not be applied over
substrates other than masonry substrates such as wood, metal, or plastics,

ELASTOMERIC COATINGS

Paints and elastomeric coatings are similar in that they always contain three basic elements in
a liquid state: pigment, binder, and solvent. In addition, both often contain special additives
such as mildew-resistant chemicals. However, paints and coatings differ in their intended uses.
Paints are applied only to add decorative color to a substrate. Coatings are applied to water-
proof or otherwise protect a substrate. The difference between clear sealers and paints or coat-
ings is that sealers do not contain the pigments that provide the color of paints or coatings.
Solvent is added to paints and coatings to lower the material viscosity so it can be applied
to a substrate by brush, spray, or roller. The binder and solvent portion of a paint or coating
is referred to as the vehicle. A coating referred to as 100 percent solids is merely a binder
in a liquid state that cures, usually moisture cured from air humidity, to a seamless film
upon application. Thus it is the binder portion, common to all paints and coatings, that
imparts the unique characteristics of the material, differentiating coatings from paints.