Not all paints adhere well to their substrates:
The degree to which the paint adheres to the substrate depends on the interaction between the two materials during coating. The strength of the bond between a substrate and a coating determines its ability to withstand its surroundings. The effect of bond strength is not easily observed with the naked eye. Therefore, ASTM paint adhesion testing is necessary to determine whether a paint will meet industry standards during its useful life.
ASTM Paint Adhesion Test Methods and Standards
We perform three main paint adhesion tests when evaluating paint resistance:
Crosscut test:
This method is used to evaluate the adhesion of one or more coatings. The process involves cutting a pattern of vertical lines through the adhesive all the way to the substrate, then laying the pressure sensitive tape over the cut and pulling it out quickly. Qualitative measurements are quickly observed and result in pass/fail or 0-5 grades according to the ASTM D3359 procedure specification.
Scratch test:
This method tests the adhesion of paints, coatings, varnishes and varnishes. It happens in a lab setting and not in the field. The method involves applying adhesive in a uniform thickness to a smooth substrate, then applying a circular stylus under increasing pressure until the adhesive is removed. Quantitative results are measured according to the ASTM D2197 procedure specification.
Pull-off test:
This method evaluates the adhesion of one or more coatings to a smooth surface by applying tensile stress from the cart to the surface (rather than the shear stress measured in the previous two tests). Slowly increase the load until the trolley and adhesive layer are removed. The procedure can also be applied on-site and provides quantitative results according to ASTM D4541 and ISO 4624 procedure specifications.
Test Methods
Pull-Off Test - This is done by sticking the loading jig perpendicular to the coating, then slowly increasing the tensile load until the jig and adhesive layer are removed or until a predetermined value is reached.
ASTM D4541
ISO 4624
Quantitative
Can evaluate single or multi-coat systems
Can be performed in the field and in the laboratory
on a flat surface
Knife Test - This process is done by making two cuts in the coating with a utility knife to create an "X" shape. Then use the tip of the knife to lift the coating at the apex.
ASTM D6677
Qualitative
Evaluated on a scale of 0-10
Based on difficulty of coating removal and size of adhesive removed
Highly viscous coatings may crack easily and appear to have low bond strength
Can evaluate single or multi-coat systems
Can be performed on-site or in the laboratory
Scratch Test - This is done by loading a circular stylus or ring into a balanced beam scratch adhesion Tester at a 45 degree angle and then increasing the load until the stylus removes the coating from the substrate surface.
ASTM D2197
Quantitative
Testing the adhesion of organic coatings such as varnishes, paints or lacquers
Can evaluate single or multi-coat systems
can only be done in the laboratory
on a flat surface
Tape Test - This is done by cutting an X-shape (Method A) or checkered pattern (Method B) into the coating, then applying pressure sensitive to the cut and removing it.
ASTM D3359
ISO 2409
also known as crosscutting test
the result is fast
Qualitative
Evaluated as pass/fail or 0-5 scale
Can be done with a knife instead of tape
Can evaluate single or multi-coat systems
ISO 17025 (A2LA certified)
