Limewash Vs Clay Plaster

Today, both limewash and clay plaster are used as architectural finishes mostly because of their inherent beauty and the feel they create. They are also both healthier options than their synthetic counterparts which may be another reason people choose to use them. Below are some of the other benefits and characteristics.

Limewash finishes date back thousands of years as one of the earliest architectural coatings. Modern day limewash looks and behaves much the same as it’s ancient predecessor, though most manufacturers today usually add some amount of an acrylic binder to give the limewash some more versatility regarding substrate compatibility. Specifically, the ability to of the  limewash to be used over sheetrock and acrylic-based primers and paints. While ancient limewash was restricted to porous substrates such as stone, masonry or even wood, modern limewash can be applied to an acrylic primer opening up more possibilities for application and use. Traditional limewash can be used exterior or interior.

In residential applications, limewash can be applied to any ceiling or wall in the home, but is not an option for wet spaces. Limewash creates an aesthetic that is truly unique and very versatile depending on the application method. Typically brushed on, brush strokes can be left, crosshatched, or removed with a light hand. If a higher sheen is desired limewash can be burnished using a trowel. Regardless the mottling and color variation within the dried finished is what draws us to limewash. The subtle movement and the way light plays upon its velvety smooth surface give it a depth our eye has evolved with, unlike the large monochromatic swaths of modern acrylic latex paints.

Limewash is certainly more environmentally friendly and has less of an impact on indoor air quality than it’s fully synthetic counterparts. As it cures, it draws carbon out of the atmosphere and hardens back into limestone. The resulting surface does not hold a static charge and doesn’t have the various plasticizers, leveling agents and other surfactants in it that would off-gas into the home. It’s inherently high pH also makes it anti-microbial.

Functionally, limewash is limestone once dried and cured. While it is hard it is porous and therefore susceptible to staining and water spotting if not sealed. For low traffic areas such as bedrooms, offices, dens etc. no sealer is required, however in hallways, powder rooms or kitchens a sealer is recommended. Sealers can be natural such an olive-oil based soap solution or wax, or if a client really wants the wipe ability of a modern day paint, a clear acrylic top coat can be applied. Touching up limewash if there is damage can be difficult as limewash builds on itself, and this variation in thickness is what creates the depth and movement in color that draws us to it in the first place.

Clay plasters offer their own unique look and feel. Much like limewash they have a mottled expression of color where light moves across the wall in subtle variations. There are more finish options with clay plasters because the aggregate size mixed with the clay can be changed to create different texture and feel. Clay plaster can be incredibly smooth and glossy to sand stone coarse and everything in between, depending on the finish technique and initial clay aggregate mix. Clay doesn’t cure but rather dries and hardens and must be compressed at the end of its application.

Clays has a positive impact on indoor air quality. The material itself (clay, sand and possibly seashell) is inert with nothing to offgas. The big advantage of clay plaster over limewash in this areas is its ability to control humidity because it is hygroscopic. Pulling in excess moisture from the air and releasing when the air dries out. Limewash does not do this in any meaningful way because it is applies so much thinner than a plaster.

Functionally clay plasters can be used in a residence, anywhere other than wet locations. Much like a limewash the finished wall is porous and can therefore water spot or stain if not sealed. Again, the same set of sealer options are available, from very natural to synthetic acrylics depending on the look and performance desired. A big advantage of clay plaster, is that it is repairable. Clay plaster may be the softest natural plaster we use, however the advantage of an unsealed clay plaster is that it is very easy to rework, add more plaster and remove scrathes, gouges etc. Marks created by the oil in our hands can be wetted and sponged off, or troweled in, new plaster is easy to work into an existing wall as wetting it reactivates the clay to where you can manipulate it and get a spotless repair.

The disadvantage of clay is that it cannot be used over a wood substrate, primer or no, additives or not. The wood just moves too much and you end up with cracking or worse, delamination. It can go over properly prepared sheetrock, and any cementious surface. It is also strictly an interior product.

Lastly, cost wise a limewash is the cheaper of the two mostly because it goes on so much thinner and with a brush. It requires less material and can generally be applied more quickly than a trowel applied plaster. The preparation of smoothing drywall and priming before hand is similar for both products, and the application of sealers is also very similar if not identical.