Civil Engineering Reference
In-Depth Information
etc.) and a polyisocyanate component. Their combination during applica-
tion from a two-head spray gun produces a polymeric structure and a vapor
that forms bubbles before the foam becomes rigid. During the chemical
reaction, it expands 20 to 30 times from its original volume within seconds.
Minimum thickness of the foam layer is 25 mm.
The use of PUF in roofing faced many problems in early years that
were related to the ambient temperature variations. On hot days, the foam
reacted too rapidly leaving a rough texture, while on very cold days it did
not react leaving the material in a liquid form. Accordingly, attention to
environmental conditions (temperature, wind, moisture on deck) is neces-
sary. PUF, once considered only as a re-roofing alternative to BUR, is now
being used in a wide range of new construction projects.
Since urethane foam is very sensitive to UV radiation, it must be
protected in some manner. Various elastomeric coatings and latex paints
have been used for this purpose. In some cases, mineral roofing granules are
sprinkled into the coating when wet. They improve abrasion resistance,
weathering characteristics, and fire resistance. Coatings must have high
tensile strength, elongation, and water transmission resistance, since water
is the foam's prime enemy.
REFERENCES
1.
Van Krevelen, D. W.,
Properties of Polymers, Their Correlation with
Chemical Structure; Their Numerical Estimation and Prediction from
Additive Group Contributions,
3
rd
Ed., Elsevier Science Publ. Co. Inc.,
The Netherlands (1990)
2.
Nicholson, J. W.,
The Chemistry of Polymers,
Royal Society of Chemistry
Paperbacks (1991)
3.
Feldman, D.,
Polymeric Building Materials
, Elsevier Science Publ. Co.,
Inc., New York (1989)
4.
Meyer, K. H., and Mark, H.,
Makromolekulare Chemie,
3
rd
Ed., Akademishe
Verlagesellschaft Geest and Patin K. G., Leipzig (1953)
5.
Turi, E. A.,
Thermal Characterization of Polymeric Materials,
Ch. 3,
Academic Press, Inc., New York (1981)
6.
Young, R. J.,
Introduction to Polymers,
Chapman and Hall Ltd., New York
(1981)
