When you build and hang up wood birdhouses your goal is to provide a comfortable environment for wildlife. Make sure the birdhouse itself is safe for the birds and protective of the environment by replacing wood finishes made of toluenes, methylene chloride or mineral spirits with these natural eco-friendly coatings.
These are produced from various seeds and nuts. The two most common oils that will harden and cure wood are linseed oil and tung oil. Linseed oil hardens quickly on wood but does not form an impermeable moisture barrier. 5 coats of tung oil on wood will form an effective water and chemical barrier. The oil finishes do not perform well on scratch resistance.
Shellac is a natural secretion from lac bugs. This secretion is collected, dried into flakes and mixed with alcohol to be applied to surfaces. It is an effective water and stain barrier, and is edible by both plants and animals, including people. Shellac does not resist scratching or heat well.
Because of their low solvent levels, water-based coatings are becoming popular for household items used by people and animals. They remain clear longer than other finishes, and repel water and stains effectively. For scratch resistance, many water-based coatings nearly equal polyurethane.