We have recently rendered the whole outside of our house with a natural finish made from clay, sand, cow poo and linseed oil. You can see the whole testing and application process here
Unfortunately, when working with cow poo on a large house, you are going to experience inconsistencies, mainly related to the cow poo. We can accurately measure the sand and clay, and the colour powder we used too, but the cow poo was the unpredictable element here.
Every day we went and collected the poo fresh, but even then the colour from poo to poo was different. As the house is so big, we can only do a section per day, meaning that we need to make a mix, use is the following week, then maybe the rest the week after, then make a new mix, and repeat. But the longer you leave cow poo the darker it gets.
So unless you make one massive mix, and have a small house, or loads of workers, then you are probably going to experience colour differences along the way (unless I guess you only use a bit of cow poo in your mix, we used 25% poop so it made a difference to the colour).
So. I decided to do some tests to see if a quick lime wash would cover all the points that I needed to fulfil. They are as follows.
- Look nice over the brown finish
- Be able to mask the colour differences of the cow poo beneath
- Be more consistent to mix in large quantities
- Hold well and not wash off with the rain
So I got back to the old test wall and applied the mix as we did on the wall. This means first applying a new mix, then when that is dry, applying an old mix, and making sure there are lines and colour differences as there are on our house.
So first I filtered my earth, which contains about 70% sand 30% clay in its raw form. It will probably loose a lot of that sand during the filtering process as the sand particles are much larger than clay. I think for a paint, the finer you make it the better. I could have filtered the earth even further to ahieve a smoother finish which brushed off less easily.
Next I mixed up my test paints. Whenever you use earthen materials for building and decorating you should do a number of tests to see how the final finish is. Even if you use the same quantities as me you will not achieve the same finish as you earth will be a different colour, with a different amount of sand amongst other things. My tests were as follows
- Ratio is – Earth:Hydrated Lime
I added a little water till it was a nice paintable consitency
They all applied really easily, with the high-earth mixes (6:1) being more gritty than the low earth mixes (2:1). They all took a really nice earthy tone when wet but they dried much lighter in the end.
As a note, you should really wet the wall down before applying your paint, and make sure to continuously mix your paint when using it as it will immediately begin to seperate between brushing.
The wall was in direct midday sun and despite this the paint did not experience any cracking despite the fact it dried really quickly.
You can just about see below that there was some colour inconsistency with the paint patches. The edges seemed to be a bit lighter than the centres of each patch. I left them to dry a few more days to see if the colour leveled out at all.
The paint worked really well, it was very easy to make and even if we made one large batch and it wasnt enough for example, we could easily replicate the colour in the next mix. The paint easily covered the changed in colour below and even filled the finer cracks of the cow poo render. It made the whole surface look more uniform overall.
The paint is not incredibly resistent to abrasion from a quick test I did rubbing the wall with my finger, but it did require a fair bit of rubbing before it started to come off.
When sprayed witha hose they all held up for about 20 seconds with a continuous stream of water at not too far a distance. I feel under conditions of rain, when the same spot is not being hit regularly, they would hold up with no problem. The 2:1 mix did not suffer at all under the hose but the rest started to fail after 10-20 seconds.
I think it is worth applying on top of our cow poo render. Once the cow poo render comes off it is very difficult just to reapply a small section as there will always be colour changes, however with the paint, small areas can be patched up, and it is really quick to apply, so it is not a huge task to repaint the house every couple of years if necessary, however re-rendering the house every few years is an enormous task. The lime earth paint can protect the render below, and when it comes to touching up in the future, there wont be problems making the right colour again.
“Surfaces suitable for limewash include:
- Lime plaster and renders
- Lime and cement based mortars and renders that have proper tooth and porosity
- Previously lime washed supports
- Masonry supports such as, brick, stone, terra cotta (mud) and cement block
Surfaces that are unsuitable for limewash:
- Asbestos cement (chemically incompatible)
- Dry wall (porosity inconsistencies and chemical incompatibility)
- Hard troweled renders and plasters (too hard for lime crystals to penetrate for bonding)
- Gypsum Plasters and products (chemically incompatible)
- Previously painted or sealed surfaces (lack of porosity, chemically incompatible)
- Smooth surface or nonpourous surfaces (no porosity, no room for lime crystals to penetrate for bonding)
- Wood (too high in PH, will cause wood grain to swell)” (source – earthpigments.com)