If your gutters or roof are rusted, water will run over them and will pick up rust particles. This will turn the water orange or yellow, which can then stain your deck if the water is allowed to run over it or pool on it. Prevent this by regularly cleaning your gutters and roof or by coating them with a rust-resistant paint. Clean rust stains on your wood deck with trisodium phosphate.
Mix 1 cup of trisodium phosphate with 1 cup bleach and 1 gallon water. The bleach will help lighten the stain and the trisodium phosphate will clean the area.
Dip a clean brush into the solution.
Scrub the rusted area with the brush. Scrub along the grain until you've lightened the rust stain. Reapply cleaning solution as needed to completely remove the stain.
Mix 118ml. oxalic acid with 1 gallon warm water if the rust stains are still visible.
Dip a paintbrush into the solution and brush it on only the rust stains. Do not brush the wood around the stains or drip the solution as this lightens any wood it comes into contact with.
Let the solution dry completely. The drying process will lighten the wood.
Rinse off the dried solution with clear water.
Let the wood air dry.
Do not mix oxalic acid in a metal bucket. Purchase trisodium phosphate from a hardware or home improvement store.