If he insists on applying a finish maybe for looks or to make the surface smoother a boat varnish from a marina would be best because it would hold up better against the sun s uv light.
Best finish for wooden outdoor furniture.
Wood or metal outdoor furniture requires a protective finish to prevent damage from moisture and ultraviolet light or uv.
Though boat owners might be willing to put up with the heavy maintenance as well as the high prices for quality formulations we don t recommend varnishes for most outdoor woodworking projects.
Since paint blocks uv rays better than a clear finish your best bet is to apply a quality exterior primer topped by a exterior latex or oil based paint.
The best finishes effectively perform this function and last a long time.
An exterior oil finish is definitely the simplest quickest way to treat an outdoor project.
Furniture patio set image.
For a natural look penetrating oil finishes might be your best bet.
On the downside it will only give you.
Types of wood penetrating finishes.
Best finishes for outdoors.
Types of film forming finishes.
Epoxy with exterior varnish.
For a natural wood look apply multiple coats of exterior spar varnish that contains added uv blockers.
Best wood finishes for outdoor furniture.
Exterior varnish or urethane.