People tend to want to make surface preparations as smooth and clean as possible. Suppose you’re looking to bond two metal surfaces together permanently. You would expect to give each side a mirror finish to have the best seal. But no adhesive in the world would benefit from having two sides bonded completely smoothly if it can instead form undercuts into the metal.
Counterintuitively, many tasks work better with rough surfaces. If you want to bond two metal surfaces together permanently, for example, a perfect mirror finish is the last thing you want. The reason is that surfaces interlock on the microscopic level, rather than just meeting on a flat plane. A piece of roughed-up metal looks more like a mountain range than a smooth, flat plain. This means that there are ‘peaks’ and ‘valleys’ – as well as ‘undercuts’ or cavities. That gives the adhesive something to flow into. For Metal bonding adhesive, visit //www.ct1.com/product-applications/metal-to-metal-adhesive/
When the adhesive cures and hardens, the bond is literally anchored to the metal surface, making it mechanically locked. There are thousands of these tiny features that you can’t even see with your naked eye. Using a smooth metal surface, on the other hand, doesn’t give the adhesive anything to really grasp. Instead, contact between the metal and the bond is purely a matter of chemistry – and chemistry has its limits.
Surface preparation is the most important step to achieve a truly strong bond. Unfortunately, it’s also often the step that most people are tempted to skip. They might give the piece a quick once-over with some coarse sandpaper and then wipe it clean with a solvent-soaked cloth to think that they’re doing the job. But the point of that sort of preparation is to transform the metal surfaces themselves, so that the adhesive can do what it’s meant to do – and has somewhere, literally, to hold on to.