Experimental Methods

Sealants

A high performance acrylic sealant and a high performance polyurethane seal­ant, both conforming to the ASTM C920-05 Class 25 specification, were chosen for this evaluation.

The polyurethane sealant was specified by the moisture-proofing contactor as part of a commercial restoration project. A two part polyurethane was cho­sen due to the low humidity in El Paso and the extended cure times required for one part polyurethanes under these conditions. The specific product selected was not the contractor’s first choice-product selection was dictated by availabil­ity at the local distributor. However, the product selected is commonly available and widely used. The contractor has had extensive experience with this product

TABLE 1—High performance acrylic sealant formulation.

Ingredient

Pounds/100 gal

Acrylic latex (63 % solids)a

567.6

Water

20.8

Surfactant

11.0

Ethylene glycol

8.2

Dispersant

3.0

Biocide

1.4

Thickener

5.9

Mineral spirits

32.2

Adhesion promoter

0.4

Calcium carbonate

536.4

TiO2

17.7

aAcrylic latex from The Dow Chemical Company, Midland, MI 48674.

and has found that it crazes more than other commercially available polyure­thanes upon weathering. However, in his experience, this crazing has not led to complaints or call backs.

A laboratory prepared acrylic sealant, based on a commercially available binder, was chosen for comparison. A laboratory prepared sealant (Table 1) was used instead of a commercially available sealant so that the authors could con­trol the formulation and understand the relationship between formulation in­gredients and exterior performance. A plasticizer free formulation was chosen to minimize sealant dirt pickup. Since contractor application preferences were unknown at the time that the sealant was formulated, no attempt was made to optimize the viscosity, toolability, or open time of the formulated material that was sent to El Paso.