What Surfaces Does Silicone Glue Not Stick To? A Quick Guide

Silicone glue (or more specifically silicone sealant) is a true hero within the world of adhesives. Flexibility and various forms of waterproofing are the primary reasons for its near universal use. However, the very versatility that makes it so useful has a significant limitation; certain materials simply do not allow for adhesion. Understanding what these ‘non-stick’ surfaces are is key to a successful project.

Key Surfaces That Resist Adhesion with Silicone Glue

The primary reason for this adhesion failure is low surface energy. Essentially, the surface is too ‘slippery’ for the silicone to ‘grab’ onto. The most common non-stick surfaces include:

Non-Porous Materials:

Smooth surfaces – glass being the prime example, specific metals and many plastics – lack any form of pore that mechanical locking by the silicone could occur within. Poor bonding is the result.

Plastics such as HDPE and Polypropylene:

Very low surface energy plastics, bonding with silicone is near impossible; these are near constant complaints in the DIY and industrial sectors.

PTFE and all types of fluoropolymers:

(Teflon® being the well known example) – the designed non-stick property is what naturally repels silicone adhesives.

Contaminated Surfaces:

Oil, grease, small dust particles or simply moisture create a near perfect barrier. Perfectly clean is a pre-requisite for any adhesive to work.

Solutions for Successful Bonding on Said Challenging Surfaces

Overcoming the previous limitations is possible through technique. Increasing surface energy and/or creating a true bondable substrate is the goal.

Meticulous Surface Preparation:

Strong solvents or degreasers (isopropyl alcohol being ideal) must be used. Complete dryness is required.

Specialized Primer:

As mentioned above, a primer is by all means the best solution for at least some of the more difficult surfaces.

Creating a Mechanical Bond:

Lightly sanding a non-porous surface will always work to some degree. Microscopic scratches are a form of mechanical bond.

Choosing the Right Silicone Glue:

High tack or plastic/metal specific adhesives are now available.

Conclusion

Silicone glue is a near perfect adhesive, but as with all things, some surfaces just won’t stick. Adhesion will always be a part of the process. Waterproof or not, a strong and/or durable bond can and should be made.