Accordingly, Bondo is a very stiff product when cured, which makes it well designed for auto bodies. Just like caulk is too flexible to effectively fill large gaps in wood, Bondo is too stiff to do the same. When Bondo (or any auto body filler) is used to patch wood, it fails in a very short time.Click to see full answer. Hereof, is Bondo flexible when dry?Bondo doesn’t “dry”; it cures through a heat-generating chemical reaction between the resin and hardener. In theory, properly mixed Bondo can be applied in any thickness, but beware of gravity-induced sagging.Beside above, is Bondo a good wood filler? Bondo All-Purpose Putty/Body Filler It’s actually made for auto body repairs but works great as a wood filler. This product gives more structure and you can rebuild chunked corners and large gouges. It comes in a quart with a cream hardener that you mix together before application. Similarly one may ask, is Bondo glass flexible? Regular filler(bondo, etc) will work better than the primer fillers for high build, because it is more flexible. Bondo glass is fiberglass and is harder to work with and has more shrinkage, its purpose is for strength.How long can Bondo be left unpainted? about 2-3 weeks