Fixing limewash problems on traditional interior walls

Working with traditional building material requires more than an off-the-shelf solution for problems. This is particularly true when it comes to the finishing detail on walls, like plastering, rendering, and painting. With the buildings at Towerwater having been built with sunbaked bricks, plastered, and rendered with a mud plaster, and painted with limewash throughout, it is important to understand the different materials used and their chemical relationship to each other. It is this knowledge, or awareness, that is essential when it comes to traditional building restoration or maintenance.

The Voorkamer limewashed with Deep Cream Limewash

One frustration encountered in maintaining the inside of the building, was that not all the walls in rooms reacted in the same way when limewashed. Although all environmental conditions were the same and the same brand of limewash was used throughout. The only variable being the selected colour shade of the limewash, differing one room from another.

The limewash on the walls in three rooms was very good and we never experienced sifting. However, in another three rooms a problem manifested where the limewash appeared to powder against the wall and constantly sift onto the floor and nearby furnishings.

To assess each room and identify anomalies that might cause this sifting, was no easy process. The rooms were all prepared in the same way prior to limewashing. The fact that the limewash contained different colour pigmentation, we thought, should not have affected the end result in that way.

Different colour limewash for different rooms 

In determining what might have gone wrong during the limewashing process, we looked closely at what could have gone wrong with the preparation of the walls and the application of the limewash. The walls were all cleaned down to remove powdery or flaking limewash. The walls were carefully dampened with water prior to, and again after limewashing, so as to ensure a slow curing process. The only variables at this stage were a possible variation in the consistency of the limewash (continuous stirring is important) and the length of time between the application of subsequent coats.

The manufacturer’s information on the drums of limewash, indicates that the limewash is ready for use after it has been stirred thoroughly. It also indicates that one can add some water to thin the limewash and that will help to apply it more easily. Multiple thin coats are preferable to one or two thick coats. I did all that the first time, so no real warning lights going on where the thickness was concerned. Did I apply the layers too soon? The manufacturer’s information indicated that it was best to let the coats dry overnight but one can paint the second coat when the first is visibly dry. Clearly, the coats were applied the correct way. The only step I might not have followed properly was to dampen the walls between coats.

The grey limewash in the drum and the end result on a bedroom wall

It did not explain why three rooms were fine and another three not.  We decided to follow every instruction to the letter when applying limewash on the interior walls this time. The walls in the first problem room were prepared by brushing with a stiff brush. After that, all the walls were vacuumed to remove any remaining dust or loose material.

The first coat of the limewash went on like a dream but as it dried, it was clear that we had not solved the sifting problem. Very despondent, we went back to our sources. We contacted the manufacturers. They could not advise us but instead freely offered two samples of their other products to apply over the limewash as a sealant. They requested that we provide feedback on our findings. Although we accepted the products, we were reluctant to use it on our walls. Sealing the walls with an acrylic water-resistant finish seemed to defeat the purpose of using limewash that expressly allows the earthen walls to breath by allowing the free passage of moisture.

We decided that the solution for a problem with a traditional product must be found in traditional usage practices. We could find little guidance and information for the use of limewash in South Africa. With the slow demise of traditional buildings in the Western Cape and the country at large, the demand for traditional building materials seems also to be reducing and with it, the associated vernacular knowledge.

Rennet Casein powder

Reading some technical advice on a British website about lime, offered some hope. Several traditional formulas consist of lime slaked and thinned to a cream to which various additions are made, such as salt, alum, powdered glue, casein (skimmed milk), etc.  Limewash that contains casein will have a better binding with the wall and the coagulation of the limewash will prevent the lime from sifting when it is dry. There is amazing information to be found about limewash and the chemical reactions of it with walls. The use of casein for architectural purposes dates to the ancient Egyptians who used lime-casein to protect renders.

Casein gives greater binding properties to clay and lime mixtures. Casein, like lime, is breathable. We decided that adding casein will provide the most likely solution to the sifting or flaking problem when the limewash is applied to the walls. A small quantity of casein added to limewash will thicken and strengthen it considerably.

Liquid rennet used in cheese making

Rennet (complex enzymes found in the stomach of a calf) and casein (a protein found in milk) are key ingredients in cheese making. Rennet casein contains casein of 100 % purity. Milk powder also contains casein but at a lower percentage, of around 80%.

After proper research, Keith set off to the largest cheese factory of the three found in our valley to enquire about buying some rennet casein in the hope of solving our limewash problem. The plant manager was very accommodating and generously provided Keith with 500g samples each of the powder products Rennet Casein and Casein with which to experiment.

Liquid rennet and casein powder

The ratio of rennet casein to limewash we found on a lime information website from the UK. We mixed 25 grams of the rennet casein powder to 1 litre of limewash. This limewash and rennet casein mixture worked like a charm. Apart from giving the wall a smooth dust free look, the limewash now also adheres to the walls without rubbing off.

Adding casein and rennet to the limewash 

For the casein mixture we used the same ratio of 25 grams of casein to 1 litre of limewash, but we added 0.166 ml (½ ml on 3 litres) of rennet. We bought a handy 100ml container of rennet from a shop in Cape Town that sells cheese-making ingredients. Adding either the ready mixed Rennet Casein or the Casein powder with the liquid Rennet product, provided the same excellent results.

The end result of using the ingredients for cheesemaking in the limewash, solved our problem. Reading about adding buttermilk to one’s limewash now makes so much sense because it is, after all, another source of casein. Knowing what casein can do for the adhesion of limewash to walls, I can understand why wall paintings from ancient Egypt still look so clear and fresh, even after the passage of thousands of years.

Adding some ingredients for cheese-making to one’s limewash does not seem so cheesy after all.

 

Sources:

https://www.lime.org.uk/  - Limewash Application Guide

https://www.readkong.com/page/paints-and-their-history-articles-printed-in-the-western-3348832 - Paints and their History

https://repository.upenn.edu/cgi/viewcontent.cgi?article=1382&context=hp_theses - Traditional Architectural Renders on Earthen Surfaces