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For the proper cleaning and maintenance of lime plaster and limewash it is very important to understand some of the basics of lime.
The key point to understand regarding traditional lime products is that they will dissolve when they stay damp and wet. Therefore, all coatings that are applied on top of lime plaster, lime mortar, and limewash must be very porous to allow them to dry rapidly. The porosity of all subsequent coatings that are on top of lime are extremely important. Coatings must prevent moisture from getting trapped in the wall, which is something modern paint and cements cannot offer. However, this also means lime finishes are not nearly as washable when compared to modern coatings such as latex paint, acrylics, cements etc.
With these basics in mind, there are several ways of making limewash and lime plaster washable during the installation process.
For Lime Plaster:
As the lime plaster is initially setting you would apply and work into the plaster a true black olive oil soap. The soap reacts with the lime and creates a waterproof and washable surface. This finish is typically called Tadelakt. The plaster can also be highly polished using a stone or stainless steel trowel. The polished finish is very washable.
Casein can be added right before applying limewash. The amount of casein added, will allow varying levels of washability.
Modern additives such as latex, acrylics, xanthan gum, methyl cellulose etc. can be added to limewash. We guarantee that no modern materials are added to our products so we will not add these types of ingredients. Our commitment is that all of our products are 100% natural. They are either directly out of the ground, and/or cleaned sieved boiled or fired. We have no modern "shortcut" chemicals added.
An important point to keep in mind is that the more washable, cleanable and waterproof the surface of the lime plaster is - the less porous it will be. This can lead to trapping moisture in the wall which in turn will defeat the purpose of using lime on a wall that needs to breath.
Solid structural masonry walls, especially those that were built with historic lime mortars must be very permeable as to not trap moisture within the wall. The basement foundations of buildings that were built using lime and earth mortars were limewashed every year or two. The fresh coat of limewash helped to prevent mold/mildew and kept the basement dry. (Lime helps to dry things out). The interior walls of the main living areas were also limewashed and with a bit of casein added to the limewash, it became "milk paint". Exterior walls were limewashed with casein or true boiled linseed oil added to the recipe. All of these coatings are breathable and porous.
I recently had someone call to let me know that they would not be purchasing any of our products for their plaster project. He said he was able to create his own "plaster" by using a combination of silicone-latex caulk, Kilz stain killer, Elmer's Glue and typical type S Lime. He said it made an amazing plaster that was easy to use and left a beautiful finish. The obvious problem with this recipe is that it defeats the purpose of staying away from modern chemicals and breathability etc.
Although there are countless modern materials available for historic solid structural masonry walls, they are will either trap moisture or contain chemicals.
The best way to clean lime plaster and limewash is to keep it from getting dirty in the first place. Stains, marks and dirt cannot be easily washed off, rather these foreign substances can be gently wiped with a dry cloth and then apply limewash over them.