How many pounds of sand does it require to sandblast 1 sq ft of metal surface?

More information is needed to answer this question. There are too many variables:

* How much compressed air do you have available (volume - cfm)? * What type of blast system are you using to blast? Siphon? Pressure? * What size blast nozzle will you be using? * What size/type of abrasive* will you be using?

* Hopefully you will not be using silica sand. The health hazards (silicosis) associated with breathing in the dust generated in the blasting process is not worth the cost savings or convenience in using that abrasive. Dust masks, air fed hoods or air fed helmets help a little bit but DO NOT 100% protect the person blasting.