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Coating Adhesion Instruments Buying Guide
Adhesion testers measure adhesion of coatings to the metal, wood, concrete, or other substrates by measuring the force (pressure) required to pull a measured diameter of coating off the substrate.
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DEFELSKO® POSITEST AT-A HYDRAULIC ADHESION TESTER KIT |
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DEFELSKO® POSITEST AT-M HYDRAULIC ADHESION TESTER KIT |
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STANDARD DOLLY ADHESION TEST KIT |
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| DEFELSKO® POSITEST AT-A HYDRAULIC ADHESION TESTER KIT | DEFELSKO® POSITEST AT-M HYDRAULIC ADHESION TESTER KIT | STANDARD DOLLEY ADHESION | |
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Why use pull off adhesion testers?
Adhesion testing belongs to the family of coating inspection tests known as destructive testing. These involve damaging a cured coating to provide a definitive answer to a query on a coating’s performance. In this instance the required test result is how well a cured coating has bonded to a substrate. An adhesion tester works by applying pulling force to a dolly bonded to a cured coating surface. The pressure at the point of failure is desired test result. Coating inspection standards will stipulate a pulling force that a coating will have to withstand to achieve approval.
Common issues with adhesion testers
- One of the most common issues with adhesion testing is fracture failure i.e. the the coating failing in an incorrect manner. This can happen several ways – the coating delaminates within itself, the bond between the dolly and the coating fails or the substrate fails rather than the bond between the coating and the substrate.
- Digital readouts will always be more accurate to read than dials or indicators. A digital readout will always provide an unequivocal result, whereas as a dial or indicator is subject to the angle of view, lighting inspectors eyesight, etc.
- Two handed or three handed use. Some test machines can be used with two hands on horizontal, vertical and over head surfaces. Others will require 3 hands when used on anything but a horizontal surface. Some test equipment that is completely self contained rather than separate pulling head and power packs can be a falling object hazard when the coating fails when used on vertical and overhead surfaces.
Important considerations when choosing the right adhesion test kit
The main consideration when choosing an adhesion testing system is the application. If you are consistently doing pull-off tests, you should invest in an automated unit that will give you the highest level of accuracy.
The manual pump system is great for regular testing, as the hydraulic pump will give you a consistent pull which is important when doing adhesion tests. The Manual Elcometer style pull off tester uses screws, and does not record the reading… We do not recommend this unit unless you are only doing occasional testing.
Frequently Asked Questions
What options are available for dollies?
The Most Common Dolly for pull off adhesion testing is 20mm. Other sizes available include; 10, 14, 29 and 50mm general purpose dollies. The smaller the dolly, the high the pull-off force (same amount of applied pressure over a smaller area increases pressure on the coating and substrate). A 50mm dolly designed for achieving optimum results on concrete. A 50mm x 50mm square tile dolly for testing tile adhesive strength.
What is the lowest strength that an adhesion tester can measure?
When utilized with a 50mm diameter dolly, naan adhesion tester is in a priming state until reaching a priming pressure of 16 psi. It is only after the priming pressure is reached that the instrument begins calculating and displaying the pull rate.
Can adhesion testing be done on flexible or brittle substrates?
Adhesion testing is designed for use with rigid, structural substrates. A flexible substrate can adversely impact test accuracy and repeatability. Using an adhesion tester for measuring the adhesion of coatings applied to a brittle substrate typically results in the destruction of the substrate material, making it challenging to quantify the coating-substrate bond strength.
