Why does polyurethane have bubbles?

Minwax polyurethane is a protective varnish that is used to seal wood stain. It is an oil-based, clear finish that is applied in several coats after staining, and it is fast drying and appropriate for any indoor wood surfaces, such as cabinets, bookcases, trim, and doors. read more

Other than this, polyurethane has a peculiar problem associated with its hardener - the hardener being isocynate, it reacts with moisture and forms carbon dioxide as byproduct. This can also be another cause of bubble. Hence it is important to check the condition of hardener. read more

Polyurethane foam (insulation and seat cushions, for example) is typically a mixture of an isocyanate (e.g. pMDI) and a resin or polyol. When these two components are mixed there is an exothermic reaction which causes expansion and growth of the material. read more

The bubbles will not have enough time to pop and any brush marks will not have enough time to flow out. How To Prevent the Problems. Thinning the finish will make it flow out better so brush marks will level and air bubbles will have enough time to burst before the finish sets up. First, make sure the finish has enough solvent in it. read more