We televised the duct work under the concrete slab, for a down draft furnace system, we found that the metal duct work in the back of the house was rusted out along with all the metal couplings/fittings used one the PVC pipe in the front of the house, we applied our spin cast mortar system to restructure the rusted out metal and applied two applications of the duct armor product leaving a nice clean breathing environment for the homeowner.