What Is A Field Adhesion Test?
Field adhesion testing is an important way to ensure quality jobsite application and surface preparation of installed sealant joints. 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. It also helps detect problems such as:
- Contaminated or expired shelf life sealant or primer
- Improper substrate cleaning or joint configuration
- Incorrect primer selection
- Poor priming techniques
- Three-sided adhesion (i.e. absence of, or improper installation of backing material)
- Excessive substrate movement
- Bond breaking material at bond lines (i.e. moisture, frost, incompatible coatings)
There Are Two Kinds Of Tests
You can perform two types of tests. One is Destructive and the other is Non-Destructive. Destructive (recommended because it’s preferred for warranties) is a hand pull test that you can use on the jobsite after the sealant is fully cured. It stresses sealant to cause cohesive or adhesive failure of the substrate where deficient conditions exist.
Below are the steps to follow:
- Cut horizontally from one side of the joint to the other with a knife
- Make two vertical cuts (from the horizontal cut) approximately 2 inches long on each side of the joint (See Figure 1)
- Pry out flap created from cuts as shown in Figure 1
- Firmly grasp flap and slowly pull at 90º from the sealant plane
- Pull flap until adhesive or cohesive failure occurs (approx. 1″)
There Are Two Types Of Destructive Test Failure
Adhesive failure happens when sealant pulls off cleanly from the substrate. Cohesive failure happens when sealant rips or fails within itself, leaving well-adhered sealant on the substrate. When the seal is interfacing dissimilar materials, run a test separately on either side of the joint. Make a third vertical cut down the center of the sealant and test each side separately. Cohesive failure is considered a positive result.
There Are Two Ways To Do The Non-Destructive Test:
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: Locating 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 of 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.
*Test guidelines are provided by Pecora Corporation. Contractors can refer to Appendix X.I of ASTM C1193, Standard Guide for Use of Joint Sealants for more guidance.
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In the video above, you see a knowledgeable White Cap Waterproofing PSS demonstrating a field adhesion test. Contact your local PSS today for assistance in performing or setting up a test to ensure quality application on your jobsite.