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VARNISH ADHERENCE - ASTM 3359:2007 (Method B) (adapted)

1. TOOLS
1.1 Sharp razor blade, scalpel, knife or other cutting device having a cutting edge angle between 15 and 30 ° that will make either a single cut or several cuts at once
1.2 If cuts are made manually, a steel or other hard metal straight-edge or template to ensure straight cuts
1.3 Tempered steel rule graduated in 0.5 mm for measuring individual cuts
1.4 Adhesive tape
1.5 Rubber eraser on the end of a pencil
1.6 An illuminated magnifying glass to be used while making individual cuts and examining the test area

2. SAMPLING
Flat samples of sufficient dimension, clean and free from varnish imperfections

3. ENVIRONMENTAL CONDITIONS
Extremes in temperature or relative humidity may affect the adhesion of the tape to the coating

4. TESTING PROCEDURE
4.1 Check sample flatness with a straight edge such as that of the tempered steel rule

4.2 Place the sample under a firm base and, under the illuminated magnifier, make cuts as follows:
  4.2.1 For coatings having a dry film thickness of up to and including 2.0 mils (50 um) space the cuts 1 mm apart and make 11 cuts unless otherwise agreed upon
  4.2.2 For coatings having a dry film thickness between 2.0 mils (50 um) and 5.0 mils (125 um), space the cuts 2 mm apart and make 6 cuts
4.3 Make all cuts about 20 mm long and just deep enough to reach the substrate under the film
4.4 After completing the cuts, brush the film slightly with a brush or tissue to remove any detached flakes or ribbons of coatings
4.5 Make sure the cutting tool remains sharp before effecting the perpendicular cuts which will conform the grid

4.6 Brush the surface again and check under the light that the substrate has become exposed
4.7 Remove two complete laps of tape and discard. Remove an additional length at a steady (that is, not jerked) rate and cut a piece of about 75 mm length
4.8 Place the centre of the tape over the grid and in the area of the grid smooth into place with a finger. To ensure good contact with the film, rub the tape with the eraser on the end of a pencil. The colour on the tape is a good indication of good contact

4.9 Within 90 +/- 30 seconds of application, remove the tape by seizing the free end and rapidly (not jerked) back upon itself at as close to an angle of 180 ° as possible

5. ASSESSING TEST RESULTS
5.1 Inspect the grid area for removal of coating from the substrate or from a previous coating using the illuminated magnifier. Rate the adhesion in accordance with the table below:

VARNISH ADHERENCE GRID TEST

Test Results Grading

CLASSIFICATION PERCENT AREA REMOVED SURFACE OF CROSS-CUT AREA FROM WHICH FLAKING HAS OCCURRED FOR SIX PARALLEL CUTS AND ADHESION RANGE BY PERCENT
5B

0% None

4B

Less than 5%

3B

5-15%

2B

15-35%

1B

35-65%

0B Greater than 65%

 

 
  
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