Coating adhesion is critical to long-term performance and durability of architectural coating systems. Poor adhesion can lead to delamination, premature coating failure, and aesthetic issues. For field evaluations, qualitative adhesion tests such as ASTM D3359 Method A (X-cut tape test) and ASTM D6677 (knife probe test) provide practical, standardized means to assess whether a coating adheres adequately to its substrate or the surface to which it was applied. Each method has distinct procedures, rating systems, and appropriate use cases depending on assessment needs.
ASTM D3359 provides standardized tape-test methods to assess coating adhesion by cutting through the film, applying pressure-sensitive tape, and removing it quickly to measure how much coating is removed. Method A (the X-cut test) is primarily used in the field.
The procedure for the X-Cut Tape Test is as follows:
1 – Choose a spot where the coating is fully dry/cured and free of visible defects.
2 – Using a sharp blade and straightedge, make two ~1.5-inch cuts through the coating to the substrate so they intersect to form an “X” at a 30–45° intersection angle (Figure 1a).
3 – Apply a 3-inch piece of pressure-sensitive tape to the X-cut and rub it firmly on the surface to ensure good contact, preferably using the eraser on the end of a pencil.
4 – Wait about 60 seconds, then pull the tape off quickly but smoothly, folding it back over itself at roughly 180-degree angle (Figure 1b).
Images adapted from ASTM D3359 X-Cut adhesion testing procedure.
5 – After tape removal, rate adhesion by the amount of coating removed from the substrate or underlying coat using the scale below. Evaluate the test area on the coated surface—not the tape backing—since incision debris is often picked up by the tape.
6 – Perform the test on two additional spots at the same test location (three total tests per location).
ASTM D6677 offers a qualitative assessment of coating adhesion by probing the cured film with the tip of a knife and evaluating how easily it can be lifted from the surface. Because the method relies on cutting and lifting rather than tape adhesion, it is useful in situations where the tape test method may be unreliable. For example, heavily chalked coatings can produce misleading results because the tape may remove only the friable chalk layer while the coating system remains in place, potentially masking poor adhesion. If a tape adhesion test is required, the chalking should be removed from the test area before testing. Otherwise, the knife test is typically a better indicator of the coating’s adhesion to the substrate or the surface to which it was applied.
The ASTM D6677 procedure is similar to ASTM D3359 Method A, but no tape is applied. After making the “X” cut, use the knife tip to probe at the intersection (Figure 2) and assign an adhesion rating from 10 to 0 (per the chart below).
Figure 2. Adapted from ASTM D6677 knife adhesion testing procedure.
ASTM International. ASTM D3359-23: Standard Test Methods for Rating Adhesion by Tape Test. ASTM International, 2023.
ASTM International. ASTM D6677-21: Standard Test Method for Evaluating Adhesion by Knife. ASTM International, 2021.
