Chris Marshall: Most wipe-on finishes that clean up with mineral spirits are thinned varnish, so you can follow Rob's advice (see below) when using other variations like Danish Oil or "tung oil" finishes, too. Minwax Wipe-on Poly isn't unique in this regard -- it's just thinned to make application with a cloth easier.


Rob Johnstone: As is often the case, there is good news and bad news. The good news is that you can apply more polyurethane over a cured coat of polyurethane and get good adhesion. The bad news is -- as your question implies -- that you need to get rid of all the layers of waxes and oils that may have built up on the finish since it has cured, as well as dirt and general grime that builds up on anything over time. (Faster in my house that most!) With that in mind, here is what I recommend. First, wash the surfaces with soap and water. Then use a good quantity of denatured alcohol and scrub the piece with a soft cloth to remove wax buildup. Then some mineral spirits or TSP as a solvent to further remove crud and corruption. Lastly, I would rub the whole surface down with something like 0000 steel wool, and then tack off the swarf which results from that process. Now you can apply more polyurethane. If you are going to use a wipe-on formulation -- and they are super easy to use -- remember that they build up very thin coats, so multiple applications are needed to get a good thick film coat.

To remove the dust nibs, and to just get a great feeling finish, check out the article at the our Finishing 101 section of woodworking.com.