Choosing the kind of paint or finish you want to use will depend on where it will be used (interior or exterior), what materials you have access to, and what look you prefer. Paints/finishes provide durability, reduce dusting of clay, and color.
In general there are varying degrees of durability different finishes will provide. I will explain the different finishes we have experimented with in order of durability:
You can choose to just leave your walls as an earthen plaster with no finish. Walls when rubbed up against will dust but it not exposed to weather conditions should hold up okay.
- Animal Dung
Using animal dung mixed with clay in finishes is a traditional practice in many parts of the world. The dung hardens the mix and provides extra durability. Fresh dung can be used or older dung soaked in water first.
- Starch Clay Paint
We recommend this kind of paint for most all interior walls. It is an easy, cheap, beautiful, mousse-like textured paint which is lovely to work with. At least for our area which has severe monsoon rains we do not recommend it for an exterior paint alone as tends to chip off when exposed to water.
For this paint what is needed is a pigment providing color, fillers that determine opacity and coverage, and some type of binder or glue that helps it to adhere to the wall. The only thing to find out is what ingredients you will use for these purposes.
Examples of pigments include using color from sifted natural clay present in your area or elsewhere, natural dyes, or powdered bought pigments. Fillers include sifted fine sand, mica flakes or dust, silica, or chalk dust. Binders or glues can be made from any kind of starch flour- rice, wheat, tapioca, rye, or potato.
We use in general sifted local clay for pigment, very fine sifted sand for filler (should be so fine it is like dust. Larger grains do not stick to the wall in our experience), and tapioca flour for our binder. These are the materials that are most easily accessible and cheapest for us but this would be different for wherever you live.
To make paint:
For making starch paste (binder):
1 part starch flour
1 part cool water
For mixing binder, filler, and pigment:
1 part powered or wet sifted clay (pigment)
1 part filler
(small amount of finely chopped straw for effect optional)
binder – amount dependent on ingredients chosen
In a bowl, mix flour and cold water. Meanwhile, in a large pot, bring water to a boil. When it comes to a boil, slowly add the starch/cool water mixture while constantly stirring mixture. Mixture will become thicker and translucent instead of transparent. You can take the spoon out and feel the texture. If sticky or feels like mucus, it is ready. Take off the heat and let cool a bit. We make our mix quite thin but you can make it thicker and then add more water to the final paint if necessary.
If you like the color of your final earthen plaster and just wish to keep that original color but make it more durable and reduce dusting, you can simply apply this starch paste onto the top of your earthen walls.
If you are using colored clay for your pigment sift it first (can be done wet and squeezed through a plastic screen or can be done dry with a screen). Sift your filler as well if it has larger particles.
Mix together your pigment and filler dry. You can do the 1 : 1 ratio recommended above or add more filler if you choose. By adding more filler you are sure to not have any cracking but we’d recommend at least 1 part filler to 1 part clay.
Take out a small amount that you can keep to use for touch-ups later. This has to be done now because once you add the starch paste, the paint can spoil and you will not be able to keep this paint but if you keep a dry mix you can always add more starch paste and use to make touch-ups to your wall later if needed.
Pour in the starch paste a little at a time mixing it in with the pigment/filler mix. We do not have a recipe for how much of this binder to add because in my experience, it depends on what other materials you are using and the consistency you prefer.
If I am using pure sticky clay for the pigment, I need to add water in addition to the binder. This is because if I only add the binder, it becomes too sticky and clumps not creating a smooth mix. If I were to add too much water, it would become too thin and without enough stickiness. This you will need to get a feel of. If we use clay from our local area which we sift ourselves it is not as pure and not as sticky. For this recipe we can just add as much binder as we wish to get to the desired consistency but do not have to add water and it turns out well.
We prefer our paint quite thin to the point where it drips when you apply. For this purpose, start to paint from the top down as to not drip on what you just finished. You can use a brush or your hands. To smooth over texture, use a damp sponge or clean damp brush. If you added mica flakes or straw, reveal them by using a clean damp sponge when the paint is still moist but hard.
Use within a few days as will start to separate and loose binding power. Can be refrigerated and will last longer that way.
Lime plasters and paints have been used for ages in many parts of the world as seen in the white finishes of thatched houses in Ireland, domes in Greece, churches of New Mexico, and skyscrapers of Yemen. Lime provides an extra layer of protection from water damage as well as reflects the sun in hot climates.
There are various books you can get on perfecting the art of applying lime plasters. We have mostly experimented a bit with lime washes here. We have found it to be pretty water resistant and durable in exposed areas.
The kind we can get here in Thailand has not been soaked yet so we need to soak it first and the longer the better. You may be able to get lime that has already been soaked and is ready to use. Lime is available at building supply stores.
We then take the lime that has been soaking and strain it out. We then let it sit for a bit until it settles. The lime water (water on top) is then used to splash on the wall. This will wet the wall and help it to attach to the wall. After this we apply lime with a brush or with hands (always wear gloves as it is corrosive to skin) to the wall. The most important thing is that it is put on very wet (like water) and in thin layers. You can come back to apply more layers for color consistency but if you put on thick layers all at once it will crack.
You can add sand, clay, or pigments to the lime for different shades. Most will all stay light as the lime makes them more pastelly.
- Linseed oil
For extra protection on exterior walls and for hardening and durability of floors, linseed oil can be applied over your earthen plaster. Linseed oil is made from flaxseeds and helps to make earthen finishes more water resistant and harder.
For an outdoor wall simply paint on the linseed oil to the earthen plaster or paint with a brush. It will darken the color which will lighten a bit when dried but will stay appreciably darker than the original color of your plaster/paint.
For earthen floors apply linseed oil as a final sealant on your final layer of flooring. It is best to apply before the mud is dry and apply many layers, thinning with mineral spirits with each layer. This will leave your floor hard and water-resistant but you will need a layer of wax in order to make it mopable.
The linseed oil we have access to getting in Thailand presently is very diluted with turpentine degrading the quality quite severely. It has still proven a good sealant for walls (even walls with no roofing) and helps on earthen floors but does not give nearly the quality 100% linseed oil can achieve.
For more information on earthen floors a good resource is Athen and Bill Steen’s short book, “Earthen Floors”.
- Linseed and beeswax
For walls that are exposed to more extreme weather conditions, a mix of linseed and beeswax may be desirable. We have experimented with this on the bottom exterior of a straw-bale house in a cold climate where snow can build up against the house. Simply melt down the beeswax and add at least 2 parts linseed to 1 part beeswax. The linseed will help dilute it to dry thinner on the wall. It is best to apply while very warm to it is good to continually keep the mixture on coals and reheat your container as you go. This mix is waterproof.
Because diluted linseed oil available in Thailand makes it so when mixed with beeswax, it has a difficult time drying and becomes sticky for quite a long time. Eventually it will dry and absorb into the wall but we found it better used on walls than floors or other surfaces you need to be in contact with.
In Thailand there is a kind of tree sap/resin used by fishermen/women to fix their boats. It is so sticky that it can seal holes. This can also be used as a sealant on highly exposed areas. We have used it primarily on outdoor benches and it has held up well.
You can buy the sap in a powder form (called “Chan” in Thai). Then mix 1 part to at least 5 parts pine oil. This mixture will be super-sticky so it is good to use gloves as it is hard to get off of your hands. Experiment with the proportions but you want it as thin as you can where you still have some sap in it. If the sap proportion is too high it will go on too thick and will be difficult to dry. It has a tendency to melt when exposed to the sun so takes an awful long time to dry in exposed areas if put on too thick.
- Rubber and sand
The newest material we have been experimenting with is using natural rubber (grown in Southern Thailand and easily available here) which has been mixed with Ammonium Chloride to keep it from solidifying and a filler/pigment for an outdoor paint or earthen floor sealant. A Thai man who attended one of our workshops and has now continued on to start his own earthen building business in the South of Thailand has been using it in his projects with great success. He claims it can be completely water repellent and gets stronger with more exposure to water and other elements.
We are new to trying it out but we like how you are able to keep color consistency and apply it like a paint allowing you to use whatever color you choose, instead of darkening walls as linseed oil does.
Mix 1 part natural rubber (while it is still malleable before made into sheets) and 1 part Ammonium Chloride (we’re not sure about this recipe as the man who made it brought us a big oil drum of it and that’s what he said he mixed but we haven’t yet mixed this part of the recipe ourselves).
Mix 1 part natural rubber/Ammonium Chloride mix with 1 part water. Mix the water in slowly while continually mixing the rubber mix as it will prevent clumps. If you dump all the water in at once it will clump and be hard to get out.
Mix 1 part rubber/Ammonium Chloride/water with as much as you want of filler/pigment (sifted sand with or without sifted clay in our case). We add usually about ….
Use a brush to apply as can be quite drippy. You can also make thicker by adding more rubber and it will then fill in cracks very well. For earthen floors add a thinner layer first to fill in dust and some cracks and then a thicker layer on top of that for strengthening.