What is the Difference Between Sikaflex 221 and Sikaflex 512

[Ian4624]

I needed to reseal the front half of the offside awning rail on my 1994 Bailey. I've done a similar job in the past on my old Musketeer. The Musketeer awning rail had a flat back surface so I used the strip on a roll mastic which squishes out as the rail replaced..
However,, the back surface of the awning rail on the Bailey is not flat (it is mostly a void with longitudinal strengthening) and it has rubber edging on it. . I've refixed it today using the strip mastic but I'm having second thoughts about it as I'm concerned that the mastic will have squished into the void instead of forming a seal.. Would it have been better to use one of the cartridge type sealants and overfill the void on the back of the awning rail? Hence the question about which of the mastics. Sikaflex 221 or Sikaflex 512 or Carafax IDL99?

 

[MichaelE]

Sikaflex is more of an adhesive so more suitable to the bonding of solar panel mounts for example, Sikaflex 512 is more of a sealant and will stick to timber and is less prove to weathering so more suitable for the use in the bonding of awning rails etc.