EN 927-7-2020 pdf download.Paints and varnishes – Coating materials and coating systems for exterior wood – Part 7: Assessment of knot staining resistance of wood coatings.
EN ISO/CIE 11664-4, Colorimetry — Part 4: CIE 1976 L*a*b* colourspace (ISO/CIE 11664-4)
EN ISO 15528. Paints, varnishes and raw materials for paints and varnishes — Sampling (iSO 15528)
EN ISO 16474-2:2013, Paints and varnishes — Methods of exposure to laboratory light sources — Part 2:
Xenon-arc lamps (ISO 16474-2:2013)
EN ISO 18314-1, Analytical calorimetry — Part 1: Practical colour measurement (150 18314.1) ISO 554, Standard atmospheres for conditioning and/or testing — Specifications
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http://www.electropedia.orgJ
— ISO Online browsing platform: available at htps//www.iso.orgJobp/ui
3.1
tannin staining
appearance of discoloration on coated surfaces caused by wood extractives in the substrate
3.2
knot staining
appearance of discoloration on coated surfaces caused by wood extractives in knots
3.3
wood extractives
low-molecular wood components soluble in organic solvents or water
3.4
sound knot
knot that, at the relevant surface, is intergrown with the surrounding wood along more than 75 % of its circumference and is free of decay
4 Test panels
4.1 Wood
The raw material [or the test panels shall be panels of pine (Pinus silvestris) free from visible cracks, blue stain, bacterial attack and rot damage. The panels shall be dried to the target moisture content of 18 % in accordance with EN 14298. The drying temperature shall not exceed 70 °C during any part of the drying schedule.
There are no specific demands on wood dimension, specific gravity, growth ring orientation, content of heartwood and surface structure; however, sawn panels 25 mm x 100 mm (thickness x width) with a considerable amount of knots is a suitable raw material.
After drying, the panels shall be stored in an atmosphere in accordance with Iso 554 at (20 ± 2) °C/ (65 ± 5) % RI-I until equilibrium has been reached, i.e. normally minimum for one month and maximally for 6 months.
From this, dried and climatized wood material test panels with a nominal size of 150mm x 74mm x mm. 10 mm are prepared with at least one sound knot with a diameter at least as large as the measuring aperture of the apparatus for colour measurement. The test panels shall be cut such that no part of the test face contains material originating closer than 10 mm from the surface of the raw material. The test face shall be “fresh”; therefore, the original wood material shall be sawn, cut or machined at least 10 mm below its original surface. A practical procedure of panel preparation is shown in EbjiireJ. The shown procedure isa suggestion, not a specification.
For each coating system under test select a minimum of 20 test panels 150 mm x 74mm x approximately 10 mm on a random basis from the available supply.
NOTE 2 The number of panels has influence on the accuracy of the test,
Plane the test face with an ordinary rotary planing machine and store the test panels (14 ± 2) days at (20 ± 2) °C/(65 ± 5) % RH with the planed surface exposed to the atmosphere of the climate chamber, (the surface shall not be obstructed).
NOTE 3 The time interval between planing and coating application has a decisive influence on knot staining. Freshly machined surfaces give a more pronounced discoloration than aged surfaces. It is, therefore, important to respect the specified two-week ageing interval.
4.2 Sampling of coating products
A representative sample of the product to be tested (or of each product in the case of a multicoat system) shall be taken as specified in EN ISO 15528.
4.3 Preparation of coated panels
Apply the coating system respecting the method and spreading rate specified by the manufacturer with the product or products under test. Normally, a white top coat should be applied. Unless otherwise specified, dry the coated test panels at (20 ± 2) GC/(65 ± 5) % RH for a period of (7 ± 2) days.
5 Equipment
5.1 Apparatus for accelerated ageing
Accelerated ageing of the coated test panels shall be performed in an apparatus in accordance with
EN ISO 16474-2:20 13.
5.2 Apparatus for colour measurements
The colour shall be measured in CIELAB colour coordinates with an apparatus with illuminant D65/10° standard observer as specified in EN ISO/CIE 11664-4. Specular gloss may be included or excluded, hut the selected principle should be stated.
6 Procedure of exposure
The coated test panels are mounted in the exposure cabinet with the coated surface towards the xenonarc lamps and exposed continuously for 72 h according to EN ISO 16474-2:2013, Method A. Cycle No. 1. Exposure period: 102 mm dry, 18 mm water spray. Black-standard temperature: (65 ± 3) °C.EN 927-7-2020 pdf download.