Sealant Field Adhesion Testing
Taking the guesswork out of sealant testing
Industry professionals have developed standardized testing procedures that are used to in identifying sealant beads with poor adhesion. These procedures are described in Standard Practice for Evaluating Adhesion of Installed Weatherproofing Sealant Joints, ASTM C1521. The results of these test methods can be used to assess the likely performance of the sealant bead and to compare the adhesion of different substrate preparations and sealant materials.Currently, there are no industry certifications that verify a tester’s proficiency in performing these tests. However, many manufacturers, engineering testing services, and White Cap can provide specialists who have demonstrated skills in conducting these procedures. Even so, it’s important for contractors and applicators to be knowledgeable on passing a field adhesion test.
What Is a Field Adhesion Test?
Contractors rely on field adhesion testing to verify that their applicators have properly applied a sealant. When an authorized field representative performs it, this test is a good indicator of the fundamental adhesive properties of a sealant on a particular substrate.These procedures also are useful to assess sealant failure conditions. The adhesive failure may be due to poor workmanship, the specific surface preparation used, the specific sealant used, poorly “installed” joint design, poor bond chemistry, or contaminated or expired shelf-life on a sealant or primer.
There Are Two Kinds of Tests
The ASTM document outlines procedures that are either destructive or non-destructive. It’s important to note that ASTM c1521 states that these procedures do not evaluate the performance of a sealant bead as a weather seal. Testing technicians should only use the test results to evaluate the characteristics of an adhesive bond relative to the cohesive strength of the sealant in a particular installation.The following two procedures are used by contractors to test for quality in different situations.
Destructive Testing
One destructive test is the “Hand Pull Test.” It’s a quick and effective assessment tool that can be performed on the jobsite after the sealant is fully cured (normally 24-hours after application). The results can provide quick feedback on a number of jobsite concerns. This is a great test to perform on a mock-up of the installation before the job starts. It allows the manufactures to provide the right sealant for the job. And contractors can use this test to determine what type of filling procedures should be used on the project.
To perform the procedure:
2. Make two perpendicular cuts to the horizontal cuts—approximately 2 inches long and parallel to each other—on each side of the joint.
3. Pry out the “flap” created by the three cuts.
4. Firmly grasp the flap and slowly pull at a 90˚angle from the sealant plane (substrate).
5. Pull flap until the sealant bead separates from the substrate.
6. Examine the removed sealant bead.
Record the type of failure that occurs upon full extension to failure and the degree of force required (little or much). If the substrate adhesion is acceptable, the sealant should tear cohesively within itself or elongate to an extension value beyond the sealant’s movement capability before failing adhesively.
The sample will provide indications on how the bond between the sealant and substrate failed.
Adhesive failure
Adhesive failure happens when sealant pulls off cleanly from the substrate. This is an indication that the following conditions should be examined:
· Was the surface prep of the joint accomplished properly?
· Is the backing material properly positioned so the sealant contact depth will prevent three-sided adhesion?
· Do you need to use a primer to create a tighter bond?
· Is the joint substrate strong enough to match the sealant?
Cohesive failure
Cohesive failure happens when the sealant rips or fails within itself, leaving well-adhered sealant on the substrate. Cohesive failure is considered a positive result.
When the sealant is placed between dissimilar materials, such as between a concrete masonry unit and clay-fired brick, you need to conduct two tests. Perform the same procedure as outlined but add a third perpendicular cut down the center of the sealant bead. Pull each flap separately. And then determine the type of failure on each sample.
Non-Destructive Testing
Contractors can use one of two non-destructive procedures to quickly assess the integrity of sealant beads on a project. Technicians push on the sealant bead, forcing the bead outward to the edge of the joint. If the bead pops out from the side of the joint or breaks away from the substrate, it’s considered an adhesive failure.
There are two techniques of Non-Destructive Testing outlined in ASTM c1521
Technique 1: Using a probing tool, depress the center of the sealant bead to create an elongation strain on the sealant joint. The depth of the depression is recorded as a percentage of the width of the bead.
Technique 2: Placing the probing tool adjacent to the sealant/substrate bond line, depress the sealant bead to the extent that it appears the sealant is about to fail cohesively. The sealant bead should be depressed in such a way that the probing tool does not contact or scrape against the substrate, nor slide toward the center of the joint.
Technique 1: Using a probing tool, depress the center of the sealant bead to create an elongation strain on the sealant joint. The depth of the depression is recorded as a percentage of the width of the bead.
Technique 2: Placing the probing tool adjacent to the sealant/substrate bond line, depress the sealant bead to the extent that it appears the sealant is about to fail cohesively. The sealant bead should be depressed in such a way that the probing tool does not contact or scrape against the substrate, nor slide toward the center of the joint.
What If Results Aren’t Satisfactory?
If field adhesion test results are unsatisfactory, work should be stopped to determine the cause and outline the scope of the problem. Ideally, you should maintain a daily log that includes each test result. The information can be used to verify high quality workmanship and can also help in finding solutions for problems that arise.In the video above, you see a knowledgeable White Cap Building Envelope Solutions Specialist demonstrating a field adhesion test. Contact your local Product Sales Specialist today for assistance in performing or setting up a test to ensure quality application on your jobsite.
Refer to manufacturer guidelines for additional details on field adhesion testing specific to their products and warranty certifications.
