How to encapsulate asbestos around water heater exhaust pipe and cinderblock wall?
The only way to tell if it is asbestos is to have it tested. Asbestos is added to all sorts of products to make them more heat resistant. If it is really old it probably isn’t asbestos though. To encapsulate it just paint it. Either house paint or some sort of runny caulking. That will encapsulate the fibers so you will really need to pick at it to have any fibers fly around. If it is a high traffic area you could then cover it with sheet metal.