Using Picklex on Sheetmetal:
Picklex gets sprayed straight from the bottle onto the metal. Spray about two or three square feet at a time then work it in with a scuff pad then wipe it with paper towels. Allowing a thick film to dry will work against you in the long run so wipe it off then allow the surface to dry.
Before I apply primer I like to scuff the dried Picklex with either sandpaper or a scuff pad to break the glaze then I apply epoxy primer. Remember not to use primer that has acid in it, this means no etch prime or anything else with acid.
Picklex 20 Technical Info Link
*Convenient easy-to-mix powder formula (Mix with hot water and applied with a spray bottle or a pump sprayer)
*Softens & cleans existing rust for removal with wire brush
*Solidifies any remaining tight rust
*Phosphatizes surface below rust
*Thoroughly Cleans and Conditions all surfaces of any dirt, oil, grease, silicon and other contaminants
*Contains no solvents and is completely biodegradable
*Using prep step will increase the performance of any paint by up to 400%
*Immediate painting of surface not required - prevents flash rust from occurring for up to 30 days
*No MSDS required for OSHA