51.   Sand off the sealer to the bare wood, and restain.

52.   Sand the worn spots to the bare wood, sanding off any gray wood.

53.   Sand the surrounding, partly worn area as thoroughly as practicable but not to the bare wood.

54.   Sand the area lightly, enough to expose bare wood.

55.   Sand to the bare wood, using a power sander.

56.   So, you will probably first have to strip off all the finish down to the bare wood by either sanding or by using a chemical paint remover.

57.   Sounds to me as though the floor will have to be completely refinished by sanding down to the bare wood and then applying a new finish.

58.   Solid color stains can be applied over old paint and bare wood, if the old paint is sanded thoroughly to roughen the finish and reduce gloss.

59.   Such treads always get badly treated by feet walking up and down, scuffing the varnish down to the bare wood.

60.   Such a stain must go over bare wood.