I finally quit guessing on smoke shelf buildup after a guy in Cleveland showed me the mirror trick
For a long time I just ran the brush and hoped I got it all on those deep smoke shelves. A guy I worked a job with in Cleveland maybe 6 months back showed me to tape a small mirror to the end of my rod and shine a flashlight down so you can actually see what's left. First time I tried it on an old brick fireplace I found a half inch of crust I would've missed with just the brush. I use a cheap 3 dollar bike mirror now and it takes an extra minute per job but the callbacks dropped to almost none over 2 months. Feels like the old timers just knew by feel and I never got that talent, so this works for me. Curious what the rest of you use for those tight spots that a brush can't really reach.