Ask the Expert Question-and-Answer Archive

by Ron Joseph

October, 2007

Polyurethaning Painted Outdoor Furniture

Q: I have just painted some wooden outdoor furniture with exterior paint  I would like to know if I can apply a coat of varnish or polyurethane or some clear coating as the last layer  I live in Hawaii and feel a top coat would be good.  Thank you very much

A: The term "polyurethane" is somewhat misleading, because there are single component, alkyd-modified polyurethanes, moisture curing polyurethanes, and of-course two component polyurethanes.  I presume that you intend to purchase a clear polyurethane from a local hardware store and apply it over the color coats. In principle, I imagine that it will be compatible, but since you haven't told me exactly what exterior paints you have already applied, I can't be sure of the compatibility.  However, you might take some scrap piece of wood and paint it with the exterior paints you used on the furniture.  Then apply the clear polyurethane and allow it to age for a few weeks.  At the end of that period scribe a deep "X" mark through the paint all the way to the wood substrate. Now try to lift the paint at the point where the "X" crosses. If the clear coat delaminates and peels off, then the two paints are incompatible.  If adhesion between the two is good, then you are fairly safe and can apply the clear polyurethane to the wooden furniture.

If several weeks have gone by since you applied the color coat. I suggest that you lightly sand it before applying the polyurethane. 

Regards,

Ron Joseph