Adhesion is an important quality of coatings that determines their durability and performance. It refers to the ability of a coating to adhere to a surface or other layers.
Why is Adhesion Testing Important?
Adhesion testing is essential to ensure that a coating will last and perform as expected. By causing the coating to fail, we can learn about the quality of the surface preparation and how well the coating has bonded. This testing provides a clear and measurable way to determine if the paint or coating is suitable for its intended use and meets the required high-quality standards.
Common Adhesion Testing Methods for Coatings
Tape Adhesion Tests and Pull-Off Adhesion Tests are two common methods used to evaluate the adhesion of coatings to substrates.
1. Tape Adhesion Tests
The tape adhesion test is a method used to determine how well a coating sticks to a surface. It involves making cuts in the coating and then applying and removing a special tape.
ASTM D3359 outlines 2 methods for testing adhesion using tape:
- Method A (X-cut): For coatings thicker than 5 mils (125 microns).
- Method B (Cross-cut): For coatings thinner than 5 mils (125 microns).
A. X-Cut Tape Adhesion Test
The X-cut tape test is often used on construction sites. A sharp tool is used to make an X-shaped cut through the coating down to the substrate. Tape is then placed over the center of the X and pulled off quickly. The area is inspected to see if any coating has been removed.
B. Cross-Hatch Tape Adhesion Test
The cross-hatch test is a quick and easy way to test adhesion. A special tool is used to cut a lattice pattern into the coating. The area is then brushed to remove any loose particles. A special tape is applied to the cross-hatched area and then pulled off. The area is inspected to see how much coating was removed. The results are compared to the ASTM D3359 standard.
Featured Product: DeFelsko PosiTest CH
2. Pull-Off Adhesion Test
The pull-off adhesion test measures the strength of the bond between a coating and the surface it's applied to. It involves attaching a fixture called a dolly to the coating and then pulling it off with increasing force. The point at which the coating fails indicates its adhesion strength. The failure usually occurs at the weakest point in the system, which could be the dolly, the adhesive, the coating layers, or the substrate. This test follows standards like ASTM D4541/D7234 and ISO 4624.
Featured Product: DeFelsko PosiTest AT
 |
 |
| PosiTest AT-M | PosiTest AT-A |
The PosiTest AT Adhesion Tester is DeFelsko's solution for accurately performing a coating adhesion test. Available in both Manual (PosiTest AT-M) and Automatic (PosiTest AT-A) models, the pull-off adhesion tester measures adhesion of coatings to metal, wood, concrete, and other rigid substrates.
The Basic Steps for Pull-off Adhesion Testing
Basic steps for pull-off adhesion test:
-
Dolly and coating preparation — clean and abrade the dolly and the coating
-
Glue and dolly application — prepare the glue, apply it to the dolly, and place the dolly on the coated surface. Allow the glue to cure properly.
-
Test area isolation — isolate the test area of the coating from the area surrounding the dolly by cutting or drilling (optional).
-
Pull-off test — perform the test
-
Analysis of the test results — examine and evaluate the dolly and coating to determine the nature of the coating fracture
Types of Adhesion Failure (Nature of Fracture)
A. Cohesive Fracture: The fracture occurs within a single coating layer, meaning the same coating is present on both the dolly face and the coated surface.
B. Adhesive Fracture: The fracture occurs at the boundary between layers, indicating that the coating on the dolly face is different from the surface coating.
C. Glue Failure: A visible separation of the glue from itself, the coating, or the dolly occurs. No coating is visible on the dolly face.
Key Differences of Cross-Hatch and Pull-Off Methods
|
Feature |
Cross-Cut Test |
Pull-Off Test |
|
Application |
General purpose, visual inspection |
Quantitative measurement, various substrates |
|
Accuracy and Precision |
Subjective |
Quantitative |
|
Ease of Use and Maintenance |
Simple, inexpensive |
Requires careful dolly preparation |
|
Cost-Effectiveness |
Inexpensive |
Moderate cost |
DeFelsko Distributor in Singapore
LFC PTE LTD is the authorized distributor of DeFelsko adhesion testing products in Singapore. Our expert team can assist you in selecting the right solutions for your specific coating needs.
Stay informed about DeFelsko products and other leading industrial inspection tools by following LFC PTE LTD on social media. You can find us on Facebook, Instagram, YouTube, and LinkedIn.
