Triage rust-pitted patio furniture, remove unstable corrosion, and prepare sound metal to the exact profile required by an exterior filler and coating system.
Use 100 grit as the restrained coarse start and move to 80 only when a controlled test proves that faster removal is necessary and recoverable.
Choose 360 for remaining refinement and 400 for a lighter final pattern only when the next process and a representative sample show that it is useful.
Use 320 grit for light correction and add 360 only when a sample shows that its finer pattern improves the handoff or reduces later work.
Choose 280 grit when small defects still require correction and 320 grit when the surface is level and needs a lighter, uniform preparation pattern.
Use 240 grit for modest correction and 280 grit for a lighter refinement step, then confirm the choice with a controlled sample and scratch-pattern inspection.
Build the grit ladder on a matching coupon, control directional strokes, and inspect the grain before scaling to full aluminum extrusions.
Choose 600 or 800 grit by the scratch that must be removed, the layer available, and the next coating or polishing step—not wet shine.
Compare 220 and 240 grit by the existing scratch, the finishing specification, and a controlled sample rather than smoothness by touch.