Page 140 - Construction Waterproofing Handbook

ABOVE-GRADE WATERPROOFING 3.29
Waterproof coatings are classified generically by their binder type. The type of resin
materials added to the coating imparts the waterproofing characteristics of the coating
material. Binders are present in the vehicle portion of a coating in either of two types. An
emulsion occurs when binders are dispersed or suspended in solvent for purposes of appli-
cation. Solvent-based materials have the binder dissolved within the solvent.
The manner in which solvents leave a binder after application depends upon the type of
chemical polymer used in manufacturing. A thermoplastic polymer coating dries by the
solvent evaporating and leaving behind the binder film. This is typical of water-based
acrylic elastomeric coatings used for waterproofing. A thermosetting polymer reacts chem-
ically or cures with the binder and can become part of the binder film that is formed by
this reaction. Examples are epoxy paints, which require the addition and mixing of a cat-
alyst to promote chemical reactions for curing the solvent.
The catalyst prompts a chemical reaction that limits application time for these materials
before they cure in the material container. This action is referred to as the “pot life” of mate-
rial (workability time). The chemical reactions necessary for curing create thermosetting
polymer vehicles that are more chemically resistant than thermoplastic materials.
Thermosetting vehicles produce a harder film and have an ability to contain higher solids
content than thermoplastic materials.
Resins used in elastomeric coatings are breathable. They allow moisture-vapor trans-
mission from the substrate to escape through the coating without causing blisters in the
coating film. This is a favorable characteristic for construction details at undersides of bal-
conies that are subjected to negative moisture drive. Thermosetting materials such as
epoxy paints are not breathable. They will blister or become unbonded from a substrate if
subjected to negative moisture drive.

Resins
Elastomeric coatings are manufactured from acrylic resins with approximately 50 percent
solids by volume. Most contain titanium dioxide to prevent chalking during weathering.
Additional additives include mildewcides, alkali-resistant chemicals, various volume
extenders to increase solids content, and sand or other fillers for texture.
Resins used in waterproofing coatings must allow the film to envelop a surface with suf-
ficient dry film millage (thickness of paint measured in millimeters) to produce a film that
is watertight, elastic, and breathable. Whereas paints are typically applied 1–4 mil thick,
elastomeric coatings are applied 10–20 mil thick.
It is this thickness (with the addition of resins or plasticizers that add flexibility to the
coating) that creates the waterproof and elastic coating, thus the term elastomeric coating.
Elastomeric coatings have the ability to elongate a minimum of 300 percent at dry millage
thickness of 12–15 mil. Elongation is tested as the minimum ability of a coating to expand
and then return to its original shape with no cracking or splitting (tested according to
ASTM D-2370). Elongation should be tested after aging and weathering to check effec-
tiveness after exposure to the elements.
Elastomeric coatings are available in both solvent-based and water-based vehicles.
Water-based vehicles are simpler to apply and not as moisture-sensitive as the solvent-
based vehicles. The latter are applied only to totally dry surfaces that require solvent
materials for cleanup.