THE MAIN BUILDING AT STATION LUNDA is now newly paneled and is supplemented with an outer panel lining around windows and doors. This has since been painted with clay paint. This is a paint that is little known, but that has an ancient origin.
In this case, the paint of the walls consists only of clay and nothing else. The clay is excavated from the Uppsala plain's reservoir of blue clay in a riverbank close by. It has then been slurried to filter out sand and coarser particles and has then been diluted with water to a suitable consistency. It is important to keep the fine particles. It is the nanoparticles in the clay that make it adhere to almost everything. I have even painted over smooth plastic and found it to stick there better than any paint on the market. The fine particles in the clay hold the color together and penetrate an outdoor panel of sawn timber. It is to some extent also possible to paint on a planed surface, but it then has less weather resistance. I have painted the underside of the porch roof and the eaves with the clay paint on that planed surface and it remains well because it is a protected surface.
The clay paint used here consists only of clay, there are no additives, no mold toxins, no binders. Only mud and water. The fine particles in the clay are in themselves a binder. It also seems that the clay reduces the risk of mold growth on the panel. So far, the samples at Station Lunda have been free of mold when they have been treated with clay. On the other hand, the clay does not provide direct protection for the wood other than lower exposure to the sun in that the particles possibly hinder the radiation and thus delay the decomposition of the wood. Moisture can pass freely and the clay paint does not provide protection but on the contrary absorbs moisture from the air, which is visible in humid weather. It does not seem that this is something negative for the panel other than that it turns gray faster than the untreated wood surface. This is probably because it retains moisture in the wood a little longer.
The house walls have thus been painted with pure clay, no additives, not even pigment. The lining around the door, window, and corner, on the other hand, has been given a dose of a little black iron oxide to give a darker shade. It is possible to create all sorts of colors with clay if it is initially as light as possible. There is pure white clay, kaolin, but it is very rare. If you add soil pigments to a light blue clay, you can get shades from gray to yellow, red and brown, but also black. Green and blue, on the other hand, are more difficult because these pigments do not occur naturally but must be produced artificially.
You apply the paint either with a wide thick facade brush or by spraying it with a simple spray gun. The advantage of the latter is that it covers better and fills in cavities such as gaps between the planks better. The spraying technology of course requires an air pressure device that consumes some energy and that makes quite a lot of noise.
The clay paint can be washed off with water and a brush. It remains surprisingly well even on horizontal surfaces that are exposed to moderate rain but can be washed off with a garden hose or high-pressure sprayer. This means that it is quite easy to repaint without scraping and without any solvent other than water.
Clay as the paint is an interesting alternative to the day market for house paints. Painting the house with linseed oil paint is an insane waste of resources. It's like covering the house with gold. Painting with clay is probably the most environmentally friendly and cheapest alternative for the aesthetic and functional treatment of a house facade. Clay is free and does not affect the environment at all because it is a pure natural product. The only cost (if you paint with a brush), is that you need to put down is some work of digging up the clay and sludge it up. However, the color is very good. A 10-liter bucket with solid clay is enough for a normal-sized house.
In the long run, the clay affects the wood by accelerating the natural graying that so nicely emphasizes the structure of the wood. If you do not want a homogeneous surface, you can wash away most of the clay pigment after a year or so and you then get a light and nice facade that looks natural gray and where the wood pattern appears.
For consultation on painting with clay, contact Station Lunda.