The ideal method for adhesion testing is the Cross Hatch Test as described in our Adhesion: Cross Hatch-Test guide. Cutting a small grid can be a little challenging, so the use of an X pattern can be a quick way to check coating adhesion.
The Test
Required Items
- Specimen to be tested – Properly applied and allowed to dry the recommended curing time (typically at least 24 hours).
- Box cutter, razor blade or other very sharp blade.
- Straight edge
- Tape (masking or painters tape will work, do not use duct tape)
Procedure
- Using the straight edge and blade, cut the surface to be tested in a line about 2-3 inches long. Use enough pressure to cut through the coating, but you do not need to cut deep into the wood.
- Rotate the straight edge and use the blade to make an ‘X’ with the first line. Do not make it a 90° angle as shown in the image below.
Figure 1: Cut X into Coating - Place tape over the intersection and press the tape down firmly.
Figure 2: Tape over Intersection - Peel the tape off quickly.
- Evaluate.
Results
The weakest points will be the acute (<90° angle) areas right next to the intersection, but the coating may also fail in small areas adjacent to the cuts.
Complete Pass
If the tape comes off cleanly with no finish removed as in the image below, the adhesion would be considered good. There is no finish missing at the intersection and a clean X is mirrored on the tape. Considered excellent adhesion, but a grid cross hatch test would be more informative.
Figure 3: Complete Pass
Suspect Pass
If there is no obvious peeling of the film, then the adhesion is probably passable. In the below example, there is some slight removal of finish at the intersection (the lighter area) and it is visible on the tape. This would be considered passing, however a cross hatch test would be advisable to confirm these results.
Figure 4: Suspect Pass
Fail
If the coating peels away at the intersection it demonstrates very poor adhesion to the substrate. Evaluate all application procedures and drying times to ensure the coatings were applied properly and retest.
Figure 5: Failed Test
