Spray-applied polyurethane foam may be applied to interiors as well as exteriors of steel buildings. In exterior applications, the SPF must be covered with an elastomeric coating for weather protection. On the other hand, when applied to interior surfaces of steel buildings, the SPF must be covered with a 15-minute thermal barrier for fire protection.
Some projects may even require the use of vapor retarders for condensation control and an attractive finish.

For a successful application of spray-applied polyurethane foam to surfaces and components of steel buildings, several general practices must be observed:

· Surface preparation
The SPF insulation system may be composed of the primer, vapor retarder, and the actual spray-applied polyurethane foam. Prior to the application of the SPF system, all the building components must be fixed firmly against movement. All the surfaces must be dry, free of loose dirt or any undesirable substance that would hinder the adhesion of any of the system components.

· Selection of primer
If the project requires a primer, selection is based on the type of substrate to be sprayed, the final use of the steel building, and the actual recommendations of the SPF and primer manufacturers.

· Selection of Vapor Retarder
Some building codes require an interior vapor retarder or insulation facing for steel buildings. The need and location of a vapor retarder are based on the following factors:

1. The design and degree of vapor transmission
a) Interior design temperature
b) Interior design humidity
c) Exterior design temperature
d) Exterior design humidity

2. The intended location of the SPF application
a) Interior wall or ceiling surfaces of steel buildings
b) Exterior wall or roof surfaces of steel buildings

(to be continued)