Better protection for wood

Coatings used to protect the exposed wooden parts of buildings have to withstand all kinds of weather. To avoid over-frequent renovation, architects, builders and house-owners are advised to look for a reliable quality label. The relevant European standard is being revised.

A weather-beaten mountain chalet might look charming – but assaults by heat and cold, rain and sunshine, will eventually destroy even highly weather-resistant timber like larch. Outdoor paint or varnish is expected to prolong the life of most types of timber, and of course stand up to years of exposure to the elements.

If the paint begins to flake sooner than the house-owner anticipated, in the worst case the paint manufacturer is likely to find himself faced with a claim for damages. House painters, producers of garden furniture, and architects are not willing to be left carrying the blame. That is why it is advisable to look for a quality label when choosing the appropriate product.

Such a quality label is awarded by the Fraunhofer Institute for Wood Research WKI since two and a half years. It is based on the authoritative but not binding European standard DIN EN 927 (coating materials and coating systems for outdoor wood surfaces). The standard is revised every five years – due this month.

“Manufacturers of wood coatings have long demanded a standard that pays greater heed to practical considerations,” stresses Guido Hora, committee chairman and head of the WKI department for surface technology. “We particularly need new definitions for sample geometry and material properties in Parts 3 and 5 of the standard.” Part 5 defines the laboratory procedures for determining the liquid water permeability of coated timber. Part 3 – recently incorporated in ISO 16053 – specifies the conditions under which open field tests are to be carried out.

Another issue that the committee members intend to discuss during the revision process is the unfortunate predisposition of paints and varnishes to flake away from the underlying surface from the edges inward, as frequently experienced in garden furniture. “Outdoor timber shouldn’t have any sharp edges, but this requirement is often ignored,” Hora reports from experience. “To limit liability for defects of this type, we need to define a minimum standard edge radius. This is likely to lie in the region of two to three millimeters.”

Before a manufacturer’s exterior wood coating product can be sold with the quality seal, it has to pass a number of tests. These can be performed by the company’s own R&D department which, given the growing complexity of consumer product requirements, is often specialized in this activity. Or companies can call on the services of an independent, certified test laboratory like the WKI. To update their knowledge, researchers meet during the 4th Woodcoating Congress to be held in The Hague (Netherlands), October 25 to 27.