A.Henri de Marne responds: First, you should find out what caused the steel saddles to stain the beams. Such stains are usually caused by water contact.
Since the steel saddles would not have stained the beams if they had been painted with a rust-inhibiting paint before installation, I assume the saddles were installed raw. You can use oxalic acid to remove the stains, but the work will be tricky because the acid solution should not come in contact with metal of any kind. You will have to mask...
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