A:The fine oak sawdust was an old style way to fill cracks and holes. It could be mixed with wood glue, lacquer sealers that some use, or polyurethane. Now there are latex fillers, in different colours to do that job. Unfortunately, this oak dust won't help you with a water mark. The mark will have to be sanded or scraped out if possible, and new finish applied. If the stain won't come out, you may need to change the affected boards.

