Bonding silicone to aluminum
Silicone does not adhere to bare aluminum on its own; the oxide layer and low surface energy make a durable bond challenging. With proper preparation and a primer, it can be achieved reliably. This article shows how to bond silicone permanently to aluminum.
In a nutshell
Clean and lightly abrade, apply a silicone primer , and then process the silicone adhesive/sealant. Where a tough-elastic, often primer-free bond is required, MS polymers are the more straightforward alternative on metal.
Why aluminum is challenging
Aluminum carries a thin, dense oxide layer, and many surfaces are additionally coated with rolling, cutting, or corrosion protection oils. Addition-curing as well as condensation-curing silicones adhere to it only to a limited extent. Therefore, two things are crucial: a clean, activated surface and a adhesion promoter that creates the chemical bridge between silicone and metal oxide.
The reliable method
- Degrease the surface (e.g., with isopropanol), lightly abrade (sandpaper P240 to P400), and degrease again. For details, see Surface preparation before bonding.
- Apply silicone primer thinly and allow to flash off: BLUESIL Primer PM 820, Primaire PM 811 or Adhesion Promoter V-2.
- Process the silicone adhesive/sealant, e.g. Elastosil E41 or the clear Momentive RTV108Q.
Silicone or MS Polymer?
| Criterion | Silicone | MS polymer |
|---|---|---|
| Temperature range | very wide (up to ~200 °C) | moderate |
| Adhesion to metal | usually with primer | often without primer |
| Overpaintable | no | yes |
| Strength | elastically sealing | tough-elastic, higher |
For paintable, tough-elastic metal bonds, MS polymers such as Merbenit HM21 or HS60 are often the better choice (background: MS Polymer and Sealants in comparison). When it comes to maximum temperature or weather resistance, silicone remains ahead. Structural bonding of aluminum without elasticity is covered in Bonding metal without welding.
Frequently asked questions
Why does my silicone come off the aluminum? Usually due to missing primer or residual oil/oxide. Clean, abrade, prime, then it adheres permanently.
Is it possible without primer? With silicone, it is rarely reliable on aluminum. If you want to work without primer, an MS polymer is the more robust option.
Which silicone is weather-resistant enough? RTV silicones are UV- and weather-resistant; the adhesion via the primer is crucial.
Consultation and samples
Tell us the alloy, load, and temperature, and we will recommend silicone or MS polymer including primer and provide a sample. Contact us or write to info@silitech.ch.
