We painstakingly stained and exterior poly’d our exterior fiberglass wood-like doors. Although the job was way more than we bargained for we were happy with the results.. that was late summer. Now we are hitting cooler months ( 0 – only -10 so far) and the poly has started to whiten and peel from the door. (we used three coats) What a mess!! Nothing that we can do over the winter, but how do I go about fixing. Am I better off stripping the remaining poly and painting over the door, or what do I topcoat the stain with? The stain is holding up well so far. I truly advise anyone that staining a fiberglass door is not a DYI project. Highly recommend the manufacturer do it.
To remove the peeling poly use a stiff nylon scrub brush and a little warm water. You can also lightly sand with a fine sanding sponge. The idea is to remove the loose clear coating and not damage the stain. Do not aggressively sand as this will harm the stain and door surface.
Now wipe down the door with liquid sander, a cleaning solvent. Paso is the best but see what is available in your area. If nothing is available use denatured alcohol.
If everything went well you are now ready to apply a new coat of clear sealer, 2 coats is best. An exterior spar varnish is much better than polyurethane. McCloskey's Man-O-War marine spar is the best.