Rediscovering the natural beauty of wood with sustainable, non-toxic, zero-VOC natural paint finishes.
This is one of a four-part series of articles on natural, non-toxic, eco-friendly wood finishes.
In the process of building a sustainable and eco-friendly casket company, we’ve had to learn a lot about eco-friendly wood finishes. The “Plain Pine Box” appeals to only so many. We’ve learned how to achieve a wide variety of beautiful wood finishes without using harmful chemicals. Most of our learning has been a matter of rediscovering the historic techniques mastered by 16th century English craftsman. In this article we’ll briefly cover the history, chemistry, and useful techniques for achieving natural painted finishes.
Milk paint is a wonderful natural wood finish for your household projects including furniture, cabinets, doors, picture frames, children’s toys, and so much more. Not to be confused with “chalk paint” made famous by Annie Sloan, milk paint is a historic paint used for centuries prior to 1900. While chalk paint is a conventional latex product with additives for unique artistic affect, the chemistry of milk paint is the combination of milk protein and calcium hydroxide. Don’t be worried by the chemical terms. Calcium hydroxide is simply lime, or calcium oxide, mixed with water to form calcium hydroxide also known as slaked lime or hydrated lime. Lime is a common naturally occurring mineral easily extracted all around the earth. When milk protein (casein) is combined with slaked lime, a chemical reaction occurs that creates a very sticky substance—this is a binder. For color, we add natural mineral pigments such as ochres, oxides, Gilsonite, cobalt, and a list of other natural pigments to get thousands of colors.
Fortunately, there are a handful of companies that do the hard work for us and make milk paint available in powder form with the protein, slaked lime, and pigment pre-mixed. Just add water, mix, let sit about 20 minutes and you have a beautiful paint! The paint is easy to work with and will keep in the refrigerator for 3-6 weeks.
Milk paint can only be applied to a porous surface like wood. If you are repainting a piece of furniture, you can either sand all of the previous finish off (such as varnish or latex paint) or you can pre-treat the surface with a primer and/or add ultra bond adhesion additive to the paint. Milk paint works by binding in the wood grain—it does not form a top coat like latex paints do. Milk paint will never check, crack, or peel if applied to a properly prepared surface. (Milk paint will flake off smooth surfaces like metal, plastic, or varnished wood.)
Milk paint layers nicely. You can get deep rich colors with 2-3 coats. Let the paint dry at least 24 hours between coats or you risk re-hydrating the first coat and lifting it off the surface. Drier surfaces in drier conditions will cure faster, of course. For interesting antique effects, try painting a base primer color and then a second color. You can easily wipe back some of the second coat with a warm wet wash cloth to get an aged or antiqued effect on your furniture.
Milk paint must be encapsulated with a top coat to protect the surface. A painted wood surface can be protected with natural oils, buffed with natural waxes, or brushed with burnishing glazes. Different techniques work better than others depending on the intended purpose of the surface. Kitchen cabinets, for example, are best protected with a natural burnishing glaze that will harden and yield a smooth matte finish that will stand up to water and clean easily. A fine piece of pine furniture might better exhibit a softness and colorful wood grain with wax over milk paint. Hardwoods work very well with natural oil finishes over milk paint.