Biochar plaster

I fell in love with earthen plasters during my cob course. It is nice to have a building material that you can wash out on the ground right next to your garden. It is nice to know what is in your home is not toxic to anyone, and the production of it is not creating any toxins elsewhere in the world.

It is nice to be able to source materials locally, to dig up my materials from the ground. This is much more affordable as well.

I have worked with clay based plasters and lime based plasters, and recently was introduced to biochar plaster. At the Ecovillage Training Center at The Farm in TN, Albert is the biochar man. I have to admit a little skepticism when first introduced to the concept of biochar, but there are so many people who report amazing results that I am sold. 

Recently the permaculture apprentices at the Ecovillage Training Center applied some clay based biochar plaster in The Prancing Poet (event space).  Albert mentioned that the biochar blocks electromagnetic radiation such as those that come from computers, microwaves etc. I was curious so I looked around and found a very interesting article on biochar plaster. 

Biochar as Building Material for Optimal Indoor Climate

by Hans-Peter Schmidt

The article mentions that biochar plaster is being used to restore old wine cellars. It regulates humidity for the wine, helps stabilize the temperature, and filters the air. 

I had yet to complete a final plaster coat on the cob bench around our woodburning stove, so I decided to do my own experiment.

I chose to use a 50/50 lime and masonry sand mix. with at least 20% biochar. The biochar was beautiful when wet, bluish-black. As lime plaster does, the biochar mix still smoothed into a nice finish after burnishing, looking almost like stone. 

I did have to baby the plaster a bit because humidity was low in the cold air, and I wanted to keep the cob at an ideal temperature for lime plaster curing so that I did not get large cracks (the last lime plaster I did was in ideal humidity and temperature and did not require water spritzing regularly as this mix did).

The plaster turned out great. I head to leave and come back to the Ecovillage Training Center, so I asked my husband to continue to spritz it for a week and keep an eye on it, then slowly decrease frequency of spritzing while it cured the our cold temperature with the stove running. I am very curious of the effect of the humidity regulating biochar on the lime plaster, but would need to try the plaster in different conditions to know that the change was related to the biochar in particular. 

I hear it is doing great and am looking forward to further biochar plaster on the walls. I will be keeping an eye on summer humidity in our home. I am looking forward to some changes in this!

Next time: More fibers, try a natural tint, do this plaster when it is warmer out!