A 30 year sweep in Denver told me to quit brushing straight up and down on clay flues
I had been running my brush straight up and down on every flue for close to 6 years, and a sweep named Ray in Denver watched me do it for 10 seconds before he stopped me. He said you have to spin the rods clockwise on clay tile liners or you just polish the same two spots and miss the shoulder of the joint, so I switched to a rotary head on a drill and my before/after photos look totally different now. Any of you run rotary on older clay liners, or do you still go by hand on the soft stuff?
Switched to a rotary head two years ago after a old timer showed me the same thing on some crumbly clay tile. The difference in the joint shoulders is night and day, and I never went back to hand spinning on the soft stuff.