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How to finish pine stair treads
Use a power sander and a medium-grade disc to sand the treads.
Attach a medium-grade sanding disc to a power sander, plug it in, and turn it on. Go over the entire surface of each tread to start smoothing out the roughness of the wood.

Available options:
[A]. Sand the treads with a fine grit sandpaper. Use an upper-grade sandpaper..
[B]. Puree medium grade sanding discs and replace old ones with finer grade sand. Sand each tread with a medium grit sandpaper..
[C]. It's necessary to sand the surface of your treads before doing anything else. This should remove the unsightly orange tint of the pine, buff out scratches, and also allow the pine to better accept the stain..
[D]. Buff out any scuffs with sandpaper. Use a paper sander and a rag or pad to buff out any scuffs..
[C].