Does silicone adhere to silicone?

When a part of an old silicone joint has to be renewed, the question is asked again and again whether the old silicone sealant adheres to the new silicone sealant. Is it possible to apply new silicone to the old silicone without completely removing the old silicone joint?
Here is the answer as to whether silicone adheres to silicone

The old silicone joint is cracked or infested with mold, because the measure seems to inject simply new silicone over the old silicone very tempting. The new silicone covers all damage to the old silicone joint, cracks, dirt or mold-infested silicone joints. However, this measure brings only short success if the new silicone ever sticks to the new silicone.
Basic chemical requirement for silicone on silicone

At least chemically speaking, it is theoretically possible that silicone adheres to silicone, but the basic prerequisite is that the silicone sealant on the same chemical basis. This means that the old silicone joint must be on the same type of crosslinking as the new silicone.

Acetate silicone on acetate silicone

Oxime silicone on oxime silicone

Alkoxysilicone on alkoxysilicone

Nevertheless, this is no guarantee that new silicone adheres to the old silicone joint. If mold was previously in the silicone joint this will also be visible on the new silicone again very quickly. In addition, dirt accumulates on the silicone joint which acts as a release agent for the new silicone.

Therefore, the risk of liability problems is very high. It should always be renewed the entire silicone joint to achieve a long-term result of the new silicone joint.
Instead of silicone on silicone, it is better to renew the silicone joint. Pull the silicone joint

In most cases, it is no longer known which silicone sealant has been used in the silicone joint. Therefore, it is no longer possible with a renewal of the old silicone joint to determine the type of crosslinking of the silicone sealant. Even if it is known, the new silicone sealant may be different from the original one as manufacturers adapt or improve their formulations. Depending on how strongly the formulation of the silicone sealant has been changed, it can lead to significant adhesion problems on the old silicone joint.

Also dirt on the silicone joint and mold attack significantly affect the adhesion of the new silicone. In addition, in a mold infestation of the silicone joint of the mold comes very quickly in the newly applied silicone to light.

Tip: Replace silicone joint in case of mold

Moreover, it is always difficult to assess the adhesion of the old silicone sealant within the silicone joint. If the old silicone joint has detached on the joint flanks, the newly applied silicone sealant will also detach there.

Conclusion on the liability of silicone on silicone

If an old silicone joint does not fulfill its purpose due to cracks, detachment from the substrate or mold in the silicone joint, it should always be completely removed. First, the silicone joint should be removed mechanically and with the help of a silicone remover. For mildew, an anti-mold spray should still be used. After a thorough cleaning with the help of Cleanprimer or possibly with a primer, the silicone joint can be renewed.

Tip: Pull instructions for silicone joints