ASSESSMENT OF THE CLOSEDNESS OF A PAINT FILM ON TIMBER

Transcription

1 ASSESSMENT OF THE CLOSEDNESS OF A PAINT FILM ON TIMBER Publication: SKH Copyright reserved

2 Publisher: Certification body SKH PO Box AD WAGENINGEN The Netherlands Tel.: +31 (0) Fax: +31 (0) Website: SKH No part of this publication may be reproduced and/or transmitted by means of printing, photocopying, microfilming or otherwise, without prior permission in writing from SKH, nor may it be used without such permission for any other purpose than that for which it was produced. Page 2 of 6

3 CONTENTS 1 INTRODUCTION MEASURING METHOD EQUIPMENT REQUIRED VISUAL ASSESSMENT OF PAINT FILM WITH ILLUMINATED MAGNIFYING GLASS MAGNIFICATION 10X LIST OF DOCUMENTS REFERRED TO... 6 Page 3 of 6

4 1 INTRODUCTION Within the timber industry, but also elsewhere where paint is applied to timber for exterior applications, it is of the utmost importance that the paint film is closed. This is necessary for technical and aesthetic reasons. For instance, water absorption by the timber is blocked to a maximum extent if the paint film is closed, and the wooden substrate has maximum protection against ageing. The occurrence of defects in the paint film such as blister formation will be minimised if the paint film is closed. Furthermore, a closed paint film has a better appearance and the cover of the final coating will be better if the paint film is closed. The National Assessment Guidelines BRL 0801, BRL 0803, BRL 0806 and BRL 0812 thus have the explicit requirement that the paint film must be closed when a product finished within the framework of the KOMO process certificate leaves the factory. Various causes can be listed for a paint film not being closed when it comes from the application and drying process: firstly, the wooden substrate: due to all kinds of irregularities such as cracks, splits, worm holes, coarse pores and contamination resulting from machining can inhibit the paint film from flowing into a closed layer. The variation within one type of timber can also be of influence. Regularity of the substrate is thus of great importance for the formation of a closed paint film; furthermore, when the paint is applied, the wet layer thickness achieved and its distribution are of great importance. The paint used must be set to the correct viscosity, the application equipment must be in order and the application procedure (duration) must be optimised; in addition, incorrect application conditions and process conditions such as flash-off, temperature, relative humidity, air speed and drying times can disrupt the process of film formation. 2 MEASURING METHOD The method consists of an initial visual assessment with a magnifying glass (10X) whereby a distinction is made between products (frames, windows, glass beads, fascia boards, sheet material or doors) with a well-closed paint film, products of which the degree to which the paint film is closed is doubtful, and products with a badly-closed paint film. The good products continue in the process (see photo 1a and photo 1c). If there is doubt about how closed the paint film is (see photo 1b and photo 1d), coupes are cut; see photo series 2. This is done perpendicularly to the grain direction at critical locations, twice per product and a maximum of 10 times per project or lot. If it emerges that the paint film is not sufficiently closed (see photo 2b), the elements at those locations where the paint film is not closed must be given a closed paint film. This can be achieved by giving those locations an extra layer of paint using a brush with an appropriate paint product that is part of a certified paint system or giving the entire element an extra layer of paint equal to the previously applied paint layer. If the paint film is observed to be sufficiently closed (photo 2a), the normal process is resumed. Of course, the paint layer at the locations of the coupes is mended. Page 4 of 6

5 3 EQUIPMENT REQUIRED Illuminated magnifying glass, magnification 10x Wood coupe tool / wood chisel / knife Template microscope with 100x magnification Flow chart assessment of closedness of paint film: 4 VISUAL ASSESSMENT OF PAINT FILM WITH ILLUMINATED MAGNIFYING GLASS MAGNIFICATION 10X 1a 1b 1c 1d Visual assessment of the coupes Images of cross sections of coupes taken with coupe tool are magnified 100x! 2a 2b Page 5 of 6

6 5 LIST OF DOCUMENTS REFERRED TO BRL 0801 BRL 0803 BRL 0806 BRL 0812 Wooden façade elements Wooden exterior doors Paint application on timber and sheet material for the building industry Wooden glass beads, nose-shaped moulding and threshold covering for wooden façade elements Page 6 of 6