Adhesion of Silicone Sealant

Question:

We are a powder coater of aluminum extrusions for the manufacture of windows. We have experienced a problem with a silicone sealant not adhering to the powder coat, as it will to the liquid finish. Can you think of any reason for this? Thank you in advance for the advice. D.S.

Answer:

Yes, I can think of several reasons for this problem. First of all, the powder coating surface is more resistant to solvents (unlike most liquid coatings) and therefore, the sealant solvent will not “bite” into the coating surface. Next the powder coating surface is smoother than the liquid surface, making adhesion to the powder coating more difficult. In this case, roughing the surface with sandpaper can solve your problem. Lastly, some powder formulations have gloss inhibitors (wax) or slip additives in them. Both of these will prevent the silicone from adhering to the powder coating. A formulation change to eliminate these additives is the best way to correct this problem.

You should test the combination of powder coating and silicone sealant before making any permanent change to your process. This is the only way to know if you solved your problem.