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A novel approach to wood coating testing

Objective

CEN/TC139/WG2 has developed a natural weathering test, prEN 927-3 for exterior wood coatings. The test is accelerated by means of an artificial defect, a "water trap", in the coated surface. The water trap has caused considerable debate, and a series of questions have been raised regarding the relevance of this challenge and whether it provided a realistic acceleration or not.

It is the aim of the project to clarify whether the objections towards the method are justified. Moreover to investigate two different approaches of transferring test results obtained in one climatic region to another.
Generally the objections against the test method have been rejected. The water trap does provide an acceleration of coating degradation, however only for one (but very important) weathering property: crack formation. No better challenge than the water trap described in prEN 927-3 has been identified. The trap does not affect the film properties moisture-regulation and adhesion, and the method may well be applied for coatings on various wood substrates. Adhesion may be assessed by the simple tape test and although the precision is low, it seems sufficient for the rating method applied in prEN 927-3 and for a classification system pending (prEN 927-2). An attempt to establish a "Climatic Index" for transfer of test results has failed. Another approach where test results are transferred by comparison with similar data for an internal standard has however been successful. The project results are valuable for the completion of prEN 927-3 (and prEN 927-2) which is expected in 1998.
A large circular test with exposure of panels coated with 9 different systems in 8 European countries is the backbone of the project. Exposure sites reach from Finland in the north to Italy in the Mediterranean region. Data from this exercise are applied for investigating the two different concepts of transferring test results between regions. Other exposure trials are designed to evaluate the water trap, comparing it with undamaged exposure panels and with differently designed panels; another is dealing with adhesion measurement, which is one of the assessment criteria in prEN 927-3. Part of the exposures are devoted to investigating the applicability of the method to different wood species, and finally one set of panels are exposed along with a parallel set of L-joints representing an approach to practical conditions, e.g. joints in wooden windows. Exposures have been carried out for 12 month periods in the main part of the project, longer in some tasks.

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Coordinator

COATING CONSULTANCY LTD
Address
Rugvaenget 23
2630 Taastrup
Denmark
 

Participants (7)

BUILDING RESEARCH ESTABLISHMENT LTD
United Kingdom
Address
Bucknalls Lane, Garston
Watford
 
Catas Srl
Italy
Address
Via Antica 12
33048 San Giovanni Al Natisone Udine
 
DANISH TECHNOLOGICAL INSTITUTE
Denmark
Address
Gregersensvej
2630 Taastrup
 
Enterprise Ireland - Trading as Bioresearch Ireland
Ireland
Address
Glasnevin
9 Dublin
 
FRAUNHOFER-GESELLSCHAFT ZUR FOERDERUNG DER ANGEWANDTEN FORSCHUNG E.V.
Germany
Address
Bienroder Weg 54 E
38108 Braunschweig
 
STICHTING HOUT RESEARCH
Netherlands
Address
1 C,wildekamp 1 C
6700 AL Wageningen
 
TECHNICAL RESEARCH CENTRE OF FINLAND
Finland
Address
Kemistintie 3
02044 Espoo