Selecting the right adhesive for your application can be difficult, with many different factors that must be considered at the outset. Whilst the type of application influences which type of adhesive should be used – 2k, 1k, flexible, rigid, tape, etc – how it is applied is equally as important. Over our 20+ years of experience in the field, we’ve gained some useful insights into the importance of application, and there are some common misconceptions…
“Use lots of adhesive”
More adhesive is not necessarily better! The effects of excess adhesive on cure are significant. When too much adhesive is applied with 1k systems like our Formoa range, the excess will squeeze out and cause problems by reducing the effective strength build up at the bond interface, because the initial moisture from the air is absorbed in curing the excess. Therefore, we would always recommend that excess adhesive is removed. As Formoa polymers cure by absorbing moisture in the form of atmospheric humidity, removing the excess will assist in faster through-cure at the bond interface. Recent tests show the effects of excess adhesive on bond strength after 24 hours.
Fig.1: Effect of excess on lap shear strength at 24 hours
As a moisture curing adhesive system, Formoa polymer cures from the outside in. The graph above illustrates this. Lap Shear number 1 had the excess removed immediately after application. After 24 hours this has started to through-cure and the lap shear strength is significantly higher than the other two lap shear joints.
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