A clean burning fire does not leave soot.
Sounds like a smoldering fire.
How was the condition of the wood?
What type of wood?
Was it dried and seasoned?
Moldy or funky wood surface?
Green (wet) wood?
Cooking at Mason-Dixon BBQ Services
Lang 84 Deluxe Kitchen known as "The Glamazon" , Custom Klose Backyard Chef... of Snot, and a 22.5 WSM
Lang 60 Mobile - The Damsel II, Lang 48 Patio - The Damsel, Bubba Keg Grill - RIP, Double Barrel Smoker and a BSKD