Many parameters contribute to the overall performance of a sealant application. Some of the most significant parameters are sealant bead size and configuration, joint movement, quality of workmanship, the quality of the adhesive bond, and the quality of the sealant material.
A sealant usually fails to perform as a weatherseal when it experiences cohesive or adhesive failure.
If a sealant bead fails, an evaluation of the total joint movement may be needed to determine if the joint sealant was strained beyond design or if the sealant failed within design parameters.
If a sealant bead fails adhesively, there is no straightforward procedure for determining the cause. The adhesive failure may be due to workmanship, the specific surface preparation used, the specific sealant used, poor x201C;installedx201D; joint design, poor bond chemistry and other causes.
Because of the complex nature of the performance of a sealant bead, an understanding of the quality of the adhesive bond is instrumental in any evaluation of sealant performance. It is critical that the test procedures used truly evaluate the quality of the adhesive bond and do not simply take advantage of the tear resistance of the sealant.
This method does not evaluate the performance of a sealant joint as a weatherseal. It only evaluates the characteristics of the adhesive bond relative to the cohesive strength of the sealant in a particular installation. Since any failures that result from use of this test method are intentionally induced, they do not necessarily mean that the sealant joint will not perform as a weatherseal.
The results of these methods are most useful in identifying sealant joints with poor adhesion. The continuous inspection procedure is also useful in the identification of places of poor joint configuration. Obvious cohesive failures are also identified. The results of these methods can be used to assess the likely performance of the sealant joint and to compare performance against other sealant joints.
The nondestructive methods are most effective while the sealant is in a state of extension due to mild or low temperatures. They are least effective during high temperature when the sealant is in a compressed condition.
1.1 This practice describes destructive and nondestructive procedures.
1.2 The destructive procedure stresses the sealant in such a way as to cause either cohesive or adhesive failure of the sealant or cohesive failure of the substrate where deficient substrate conditions exist. The objective is to characterize the adhesive/cohesive performance of the sealant on the specific substrate by applying whatever strain is necessary to effect failure of the sealant bead. It is possible that the strain applied to the sealant bead may result in the failure of a deficient substrate before effecting a failure in the sealant.
Note 18212;The destructive procedure requires immediate repair of the sealant bead. Appropriate materials and equipment should be available for this purpose.
Note 28212;Sealant formulations may fail in cohesion or adhesion when properly installed, and tested by this method. The sealant manufacturer should be consulted to determine the appropriate guidelines for using this method.
1.3 The nondestructive procedure places strain on the sealant and a stress on the adhesive bond. Though termed nondestructive, this procedure may result in an adhesive failure of a deficient sealant bead, but should not cause a cohesive failure in the sealant. The results of this procedure should be either adhesive failure or no failure.
Note 38212;The nondestructive procedure may req......