You may know that it’s difficult to get a decent sealant joint on Henry Blueskin.
This is not surprising, though. Blueskin SA is made of polyethylene, a surface to which most sealants do not adhere.
Dow Corning 758 Silicone Weather Barrier Sealant is one of only a very few sealants on the market that can adhere – unprimed – to polyethylene and give a long-term solution that does not break down over time.
See dow’s tech note:
But, be sure to note that 758 only has 25% movement capability, which may not be enough for your needs. For example, if you have a 3/8″ joint, sealed with 758, and your joint moves more than 3/32″, then your sealant joint may break. Essentially, this sealant is only good for non-movement joints. For a movement joint, you’d have to use a different sealant. Some sealants have up to 50-100% movement capability.
Here are some useful links when designing joints:
Brick Industry Association: Calculating expansion joints in brickwork