Significance and Use
4.1 Coatings, to perform satisfactorily, must adhere to the substrates on which they are applied. This test method has been found useful as a simple means of assessing the adhesion of coatings. Although this method is a qualitative and a subjective test it has been used in industry for many years and can provide valuable information.
4.2 Other adhesion test methods may be useful in obtaining quantitative results. See D2197, D3359, D4541, and D7234.
4.3 The Performance Evaluation Scale (see 7.4, Table 1) is based on both the degree of difficulty to remove the coating from the substrate and the size of removed coating.
TABLE 1 Rating System
Coating is extremely difficult to remove; fragments no larger than approximately 0.8 by 0.8 mm (1/32 in. by 1/32 in.) removed with great difficulty.
Coating is difficult to remove; chips ranging from approximately 1.6 by 1.6 mm (1/16 by 1/16 in.) to 3.2 by 3.2 mm (1/8 by 1/8 in.) can be removed with difficulty.
Coating is somewhat difficult to remove; chips ranging from approximately 3.2 by 3.2 mm (1/8 by 1/8 in.) to 6.3 by 6.3 mm (1/4 by 1/4 in.) can be removed with slight difficulty.
Coating is somewhat difficult to remove; chips in excess of 6.3 by 6.3 mm (1/4 by 1/4 in.) can be removed by exerting light pressure with the knife blade.
Coating is easily removed; once started with the knife blade, the coating can be grasped with ones fingers and easily peeled to a length of at least 6.3 mm (1/4 in.).
Coating can be easily peeled from the substrate to a length greater than 6.3 mm (1/4 in.).
4.4 This test method does not have a known correlation to other adhesion test methods (pull-off, tape, etc.).
4.5 A coating that has a high degree of cohesive strength may appear to have worse adhesion than one that is brittle and hence fractures easily when probed.
4.6 This method is not to be used on overly thick coatings, that is, those which cannot be cut to the substrate with a utility knife in one stroke.
1.1 This test method covers the procedure for assessing the adhesion of coating films to substrate by using a knife.
1.2 This test method is used to establish whether the adhesion of a coating to a substrate or to another coating (in multi-coat systems) is at a generally adequate level.
—The term “substrate” relates to the basic surface on which a coating adheres (may be steel, concrete, etc. or other coating).
1.3 This method can be used in the laboratory and field.
1.4 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
D2197 Test Method for Adhesion of Organic Coatings by Scrape Adhesion
D3359 Test Methods for Measuring Adhesion by Tape Test
D4541 Test Method for Pull-Off Strength of Coatings Using Portable Adhesion Testers
D7234 Test Method for Pull-Off Adhesion Strength of Coatings on Concrete Using Portable Pull-Off Adhesion Testers
adhesion; coating; intercoat adhesion; knife adhesion; paint; wet adhesion;
ICS Number Code 19.040 (Environmental testing); 25.220.01 (Surface treatment and coating in general)
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Citing ASTM Standards
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