Peeling varnish problems

Spar or marine varnish looks great at first because it’s a thick, film finish that brings out the natural colour of the cedar. But, if subjected to constant sun, rain, snow or other elements, it can break down within a year or two. My problem with using a film finish outdoors is that it peels off the surface in pieces. It’s hard to make the surface look perfect again without chemically stripping the old finish off, or removing it mechanically by sanding or power-washing. It can be a lot of work.

Using a penetrating oil finish, such as an exterior-grade stain product or Danish oil (with UV inhibitors added) might not last any longer, but at least it doesn’t peel off when it fails. It just wears off. So, you can renew it at any time by sanding lightly and applying more finish. There is no need to remove the old finish to renew it.

There is a good chance that your lumber wasn’t dry enough, either, as it can take a year or more to air-dry lumber–depending on the thickness. Excessive moisture inside the wood will cause a film finish to peel off as the moisture works its way out of the wood. Also, finishing parts on all sides, including the end-grain, will help a lot. This step prevents moisture from wicking in from the underside and then peeling the finish off from the inside out.