Determination of the adhesion of paint on wood

Transcription

1 SKH Publication d.d Replaces SKH Publication Determination of the adhesion of paint on wood Edition: SKH Postbus AD Wageningen Tel Fax: Webadress:

2 Page 2 of 10 THIS DOCUMENT IS AN ENGLISH TRANSLATION OF SKH PUBLICATION 05-01: IT DESCRIBES A METHOD OF DETERMINING THE ADHESION OF A PAINT FILM ON WOOD BY MEANS OF A DOUBLE CROSS CUT TEST AND TAPE. THIS METHOD IS CURRENTLY LEADING IN THE DUTCH JOINERY INDUSTRY INDEX 1. Preface Scope Normative references Principle Apparatus and materials Wood moisture measurement equipment sharp cutter knife Tape Samples Procedure Determination of wood moisture Cleaning of testsurface Making a double cross cut Wetting (optional) application and removal of the tape Results Test report... 10

3 Page 3 of PREFACE This document is prepared by the Commission Verf op Hout (Paint on Timber), of which the secretary is conducted by SKH. This method is accepted by: Nederlandse Bond van Timmerfabrikanten Vereniging van Verf- en Drukinktfabrikanten FOSAG SKH SHR COT bv (Centrum voor Onderzoek en Technisch Advies) Verf Advies Centrum VAC Vereniging voor Oppervlaktetechnieken van Materialen VOM TNO Industrie This publication replaces SKH Publication The most important difference is that the assessment scale is turned 2. SCOPE This publication describes the determination of adhesion of paint on wood and woodlike materials. This method cannot be compared to ISO 2409 ( gitterschnitt ) and ISO 4624 ( pull-off test). ASTM D 3359 (single crusscut) is a method for steel and the method described below is suitable for wood and woodlike materials. This method is considered to be appropriate for determining the adhesion of both new and old paintfilms. By using this method the substrate is damaged as least as possible. Therefore the result is minimal influenced by the substrate. 3. NORMATIVE REFERENCES - ASTM D 3330 Standard Test Method for Peel Adhesion of Pressure-Sensitive Tape - ASTM D 3359 Standard Test Methods for Measuring Adhesion by Tape Test - NEN-EN-ISO NEN-EN-ISO NEN 5461 Qualitydemands for wood (KVH2000); cutted wood and logs; general - NEN-EN Humidity of a piece of cutted timber; Part 2: Approach using a electrical humidity measurement equipment - NEN-EN Logs and cutted wood Method to measure the humidity- Capacitive method for defining the moisture content of a piece of cut timber 4. PRINCIPLE A double crosscut is made through a paintfilm on which a tape is applied with sufficient adherence. Afterwards the tape will removed and with an assessment scale it will be determined how much paint is removed.

4 Page 4 of APPARATUS AND MATERIALS 5.1 Wood moisture measurement equipment The Wood moisture measurement equipment should be conform the requirements of NEN-EN sharp cutter knife The used knife should be that sharp that besides the cuts no other damages to the paint or timber should be obtained. A new cutter knife is fulfilling this demand. 5.3 Tape Within this method it is assumed that adhesion between tape and paintfilm is significant, therefore a statement can be made on the adhesion between wood and paintfilm (see also ASTM D 3359 Appendix X1). The tape has an adhesion strength of 10 (+/1) N at a width of 25 mm, determined according to ASTM D The used tape should not be older than one year and should be stored according to the supplier s specifications. 6. SAMPLES The determination of adhesion should be done on defect-free wood, this means the adhesion should not be determined on cracks, fingerjoints, lameljoints, knots or other damages of the wood. The obtained values there, are not representative for the adhesion. The adhesion of the paint system can be determined if the paint system is older than several weeks. If the adhesion should be determined after one week, the paint system should be dried at least 7 days at a minimum temperature of 23 C and a relative humidity of maximal 50%. To determine the adhesion of a paint system, the measurement should be done on several places of the object. One should take into account the weathered areas, overhangs and balconies. The adhesion should be determined on both the vertical as the horizontal planes. Determinations of adhesion are representative if: - determinations have been performed on all sides of the object - at least 2 determinations per wind direction for every type of surface (horizontal vertical, upper, lower) have been executed. - at least 5% of the objects is investigated

5 Page 5 of PROCEDURE 7.1 Determination of wood moisture To determine the adhesion of a paint system on wood it is important to know the wood moisture. The wood moisture influences the adhesion of the paint system. The wood moisture is determined as described in NEN 5461, Appendix A. Remark: This method will be replaced in future by NEN-EN Remark: As alternative method NEN-EN can be used. 7.2 Cleaning of testsurface The testsurface should be cleaned and degreased with an appropriate cleaner, and dried with a tissue. Remark: the humidifying time should be that short that it does not influence the adhesion of the paint on the wood. The cleaner may not influence the adhesion between the tape and the coating. 7.3 Making a double cross cut To determine the adhesion a cut is made with a sharp cutter under an angle of 30 in the direction of the fibers and perpendicular in the coating, according to Figure 1. A template should be used as shown in Figure 2. A cut is made through the coating and as least as possible in the timber. The length of the cuts is approximately 7 cm. Figure 1 Pattern of cuts. The distance between the parallel lines are approximately 1 cm and the sharp corner between the lines is approximately 60.

6 Page 6 of 10 Figure 2 Template on full size 7.4 Wetting (optional) The wet adhesion of the coating system is determined after application and drying of the coating system. According to the method in 7.3 a double cross cut is made through the coating in the timber, followed by 1 hour of wetting of the cruss cut by a piece of cotton or filterpaper soaked with water. Afterwards the surface should be thoroughly wiped dry before an adhesion test according to the method described in 7.5 can be performed. 7.5 application and removal of the tape The tape is applied on the cuts in the length direction of the diamond, strongly pressed by the fingertips. The tape has then a uniform color. After 60 seconds the tape has to be removed from the substrate in one fast and continuous movement under an angle close to 180. The removed tape should be applied on a transparent sheet.

7 Page 7 of RESULTS The assessment of the adhesion test will be done on the removed part according to the scale in Figure 3 on both the removed paint at the tape as the remaining paint on the wood. The area for assessment is 30 x 40 mm around the diamond. Scale Example Description 0 The edges around the cuts are smooth; none of the crosscut intersections have delaminated 1 Small parts of the coating have delaminated around the crosscut intersections; not more than 5% of the coating is removed

8 Page 8 of 10 2 Along the cuts and around the crosscut intersections the coating has delaminated; between 5 and 15% of the coating is removed 3 Along the cuts and around the crosscut intersections and/or on other places the coating is removed; between 15 and 35% of the coating is removed

9 Page 9 of 10 4 Along the cuts and around the crosscut intersections and/or on other places the coating is removed; between 35 and 65% of the coating is removed 5 More than 65% of the coating is removed Figure 3 Assessment scale for adhesion. Dark areas represent removed paint. An adhesion of class 1 shows that the adhesion of the paint film on the substrate (wood or another paint film) is sufficient good for applying another layer. An adhesion of class 3 or 2 means that consultation is necessary. The client should discuss with the expert which activities are necessary. At an adhesion of class 4 and 5 the adhesion is insufficient and the paint film should be removed.

10 Page 10 of TEST REPORT The test report should contain at least the following subjects: a) A reference to this publication b) The investigated paint system c) The wood moisture d) The age of the substrates e) The used tape f) The amount and the place of the examined samples (in case of an object), date of the test and the research on the test g) The average adhesion h) The type of adhesion failure (wood or intercoat) i) Individual assessments j) The test method (dry, wet or both) k) possible deviations of this publication