elastic duct mastic

Big Will

We are about 3/4 of the way through a large job with 20 hydro air systems.

6 Of the systems have duct outside of the building envelope so they have to be duct tested. We have been pre testing before drywall and having a really hard time. The house is a huge custom that is changing daily. Because of this the duct is constantly being altered to allow framing lighting and any other change you can dream up. The problem is the duct is all S and drive steel and the joints are sealed with a paint on 181 duct mastic. I have tried two different brands from my local wholesaler one is hardcast and I cant remember the other. Both have cracked in numerous places after the duct was altered down the line. The runs are all very long with lots of joints. So what would normally seam like a few minor leaks adds up to higher than the allowable percentage. I need something that can handle a little flex.



Anyone?