We just bought a 13-year-old, hand-hewn log cabin (bottom) with knotty pine timber frame on top. Some interior wood (floor boards & joists)do NOT look sealed (dull or flakey), but many rooms were sealed (shiny). QUESTION: How do we safely clean & seal the remaining interior wood? Some of the floor joists have ‘splinters’ & black areas (Is this mildew or black mold?)