can silicon be 'bonded' to rubber and how much would be required to form a heat proof coating ?

Question

require thickness to be no more than 3 mm is this possible - ?

Answer 1

Depending on the temperature you expose the rubber, Yes indeed the 3 mm thickness will be sufficient for a thermal exposure up tu 200 - 270 Centigrade. I believe it goes a little up even more with the temp.
Dfriend:)

Answer 2

You simply can't make a "heat proof" coating. Every material has a thermal limit after which its insulating or elastic properties change dramatically.

Note that the flexibility of rubber will be negatively impacted by the addition of a silicon coating; the silicon is not an elastic compound. This means the rubber cannot be bent, formed, or otherwise mechanically stressed across the coated surface. It MAY manage to withstand a compressive loading (normal to the silicon film additive).

How much of a material is necessary to provide "heat proofing" is dependent on the temperature you're trying to protect against. In general silicon has a higher withstand capability than rubber ... but it won't proof the rubber compound against ultimate incineration. The silicon won't disintegrate, but the rubber will effectively 'burn' inside the coating - or burn off entirely, if the rubber is not coated on every surface.