Sealing Ducts

[westark]

Has anyone attempted to fix and seal any duct work. I got a call from a hospital to clean, but the engineer said they might have some leaks in their ducts. Just wondering the best way to seal, there has to be more to it than sealing HVAC ducts. Should be interesting, 40ft horizontal and 4 stories vertical. I will try and post pics once I go and inspect. Thanks for the help.

[Alexy]

Weld it. If it is leaking it is a huge fire hazard. Grease will liquify and drain out if a fire or heat hot enough is ever intorduced in the duct. If you need to just close a crack for the cleaning before it is welded ( Very highly reccomened you co-ordinate this with the cleaning so it can be done at your completion) use plumbers putty it will hold up under water but not pressure.