Roof Coating Adhesion Test

A roof coating adhesion test is a field-applied test for coating performance. Roof coatings need positive adhesion to work. An adhesion test usually helps rule out any incompatibilities with the substrate.

Why Test for Coating Adhesion?

An elastomeric roof coating may have excellent physical properties (elongation, tensile strength, etc.) but for the roof coating to work, they must adhere to the substrate on which they are applied. The common methods of coating adhesion testing are performed with a knife, tensile test with fabric or with a pull-off adhesion tester.

How much adhesion is enough?

The more adhesion the better. Since this is a qualitative test, a frame of reference is valuable, if possible. For instance, measure adhesion of a roof coating to a substrate with and without a primer; or compare two different cleaning methods; or compare two or more different products (perhaps a polyurethane and an acrylic).

After any test, determine if the bond failure was adhesive (between roof coating and substrate) or cohesive (within the coating film).

Field Adhesion Testing with Polyester Fabric

To perform coating adhesion tests in the field, we recommend the tensile test with roofing fabric. The initial adhesion measured in this test does not mean that long term adhesion is assured but it does provide a strong indication of adhesion performance.

1. Clean test area thoroughly and let dry.
2. Do not perform a coating adhesion test on a rusted roof surface without rust treatment or primer. Silicone coatings should be mechanically removed from substrate.
3. Apply 15 mils of roof coating on the prepared or primed surface (min 6"x6").
4. Embed a 2"x6" swatch of polyester fabric into the roof coating. Allow 2" of the fabric to hang free.
5. Apply another 15 mils of roof coating on the fabric until it is completely concealed.
6. Allow roof coating to dry and cure for at least 3 days. (10 days recommended.)
7. Test for roof coating adhesion by pulling the fabric at a 90 degree angle to the substrate surface.
8. Some roof coating should remain on the substrate (see picture below). A clean pull indicates weak roof coating adhesion on the tested substrate.