PVC and the Weather

Testing and past field experience studies have concluded that when conventional Type I, Grade I (Cell Classification 12454) rigid PVC pipe is exposed to UV radiation from sunlight the following conditions have been noted: The effects of exposure to UV radiation results in a colour change to the product, slight increase in tensile strength, slight increase in modulus of tensile elasticity, and a slight decrease in impact strength. UV degradation occurs only in the plastic material directly exposed to UV radiation and to extremely shallow penetration depths (frequently less than 0.001 inch). UV degradation does not continue when exposure to UV is terminated. UV radiation will not penetrate even thin shields such as paint coatings, clothing or wrapping. Based on these studies, it maybe recommended that PVC and CPVC piping products (i.e. pipe, duct and shapes) exposed to the direct effects of UV radiation be painted with a light coloured acrylic or latex paint that is chemically compatible with the PVC/CPVC products. Compatibility information should be confirmed with the paint manufacturer. The use of oil-based paints is not recommended. When painted the effects of exposure to sunlight are significantly reduced, however, consideration should be given to the effects of expansion/contraction of the system caused by heat absorption in outdoor applications. The use of a light coloured, reflective paint coating will reduce this affect, however, the system must also be designed and installed in such a manner to reduce the effects of movement due to thermal expansion. Information concerning expansion and contraction, proper hanger support spacing and other design criteria can be found in this engineering and installation...