I have used 2 coats of a clear polyurethane on my hardwood floor and the second coat is covered in fine pinhead bubbles. Why?
The most common cause of this problem is that a sealer coat was not used. A sealer coat will choke the grain to stop air bubbles getting trapped. A second cause of this problem is moisture before or between the coats. When removing sanding dust, never wipe the surface down with a cloth dampened with water (unless using a water based clear). Only use the specified thinners. Having the area as dust free as possible also helps eliminate imperfections in the coating.
