Time tests PVC and polycarbonate sheets
This is a part of the Building materials feature
Two long-running BRANZ studies are investigating the durability of rigid PVC wall claddings and polycarbonate sheeting products. How are these materials lasting, and what can we learn?
Clear polycarbonate (PC) sheet is mainly used in building as an alternative to glass or acrylic. Sheets may be twin-walled and are lightweight, resistant to impacts and have good initial transparency. Rigid polyvinyl chloride (PVC) cladding products are also lightweight and generally do not require painting or lengthy maintenance. They are resistant to moisture, rotting and insects.
When used as part of the building envelope, both materials are usually required by the New Zealand Building Code to have a durability of 15 years. As these materials degrade under New Zealand’s high ultraviolet (UV) levels, the formulation of the material and choice of correct UV stabilising coatings or additives is crucial to achieve an acceptable service life.
Tests and latest results
PVC wall claddings of various colours were installed on the BRANZ exposure site at Judgeford in 1989. In 1992, 20 different imported PC sheeting products were also set out beside these. The sheets were fixed at an angle of 45° onto weathering racks facing north. Some of the flat sheets are bent to simulate the physical stress encountered in barrel vaulting, with a minimum radius of 200 times the sheet thickness.
In 1998, we reported on these two BRANZ studies (see Build September/October 1998, pages 38–39).
When tested 11 years after installation, the PVC claddings retained their tensile strength, and after 18 years, the remaining samples are still satisfactory. The impact strength has declined after 18 years and is quite low. However, all claddings remain undamaged by hail or other hard body impacts.
The PC sheeting has now become brittle, but has not been broken by hail or other impacts. Some delamination of the protective coatings can be seen on some samples, and most samples are now very hazy. This haze is caused by surface microcracking, which also reduces the impact strength of the sheet.
Guidance for specifiers
As expected, the performance of the PVC cladding is dependent on the PVC formulation. Some claddings will perform much better than others based on formulation alone. PVC pigment suppliers are generally able to offer guidance on optimising formulations.
The main lessons for specifiers are that:
- white PVC claddings out-perform darker colours from the same manufacturer
- the greater the roof pitch, the better the PC sheets retain their properties
- PC sheet durability depends on the quality of the protective coating on the surface of the sheets facing the sun
- PC sheets with protective layers of acrylic coating appear to weather better than surfaces that only incorporate UV light absorbers
- barrel vaulting does not appear to significantly affect PC sheet durability, but the part of the sheet closest to the horizontal weathers the fastest
- lighter coloured PC sheets consistently out-performed their darker coloured equivalents.
The PC sheeting and PVC cladding samples remain on the BRANZ exposure site, and their durability will continue to be the studied into the future.
Note
These projects are funded by Building Research.
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