Cow Dung for Cob house Plaster?

Hello I am working on re-plastering a small cob house that over the summer in western North carolina experienced significant loss of external plaster on more exposed sides of the house and am looking to repairing with a mix containing our local cow dung, I am here to receive feedback on how to approach this idea, what questions should I be asking to determine if this is an appropriate idea to use cow dung? Does anyone have insight and experience in cow dung mixed plasters, as well as fermenting mixes using whey? Thanks y'all I thank you for your time.

Has Cement floor, built summer 2012
Unknown mix used for plaster
More protected area's seem to have remained intact
Cob house is used as tool shed

I can't offer good advice on the plaster, but you definitely need a bigger roof. Adding tin awnings and something to prevent splash (groundcover of choice) would reduce any future issues.

I understand the hesitancy to make a proper size roof given the cost of most roofing materials, but it is a really critical piece to avoiding future problems.

R. Scott, how large a roof overhang would you recommend? Not trying to be argumentative, but to my eye the picture looks to have about a 2 foot overhang on the roof now, which I would have thought was pretty substantial....

If that is two feet, it looks like it needs 4-5 feet total on that side, just based on the plaster damage. There isn't a hard and fast rule, but it depends on height of building and strength of the wind during rain events.

ETA--Although the "damage" could be because of a bad batch of plaster. Is that where they started and maybe had a learning curve?

Cow dung can be added to earthen plaster, but horse manure is generally better. That said, I don't think manure is going to make the plaster any more resistant to rain, especially driving rains. I see from the photos that there is considerable erosion of the earthen plaster. I would recommend a finish coat of lime-sand plaster. We describe this technique in our book, The Natural Plaster Book. Lime-sand plaster turns to limestone over time and makes a really weather proof exterior plaster.

Another way to protect the wall and prevent erosion is to build a shed roof off that side of the building. It could create a porch or a place to store wood. Just increasing the overhang isn't going to protect the exterior wall. As you can see from the pictures the damage is on the lower portion of the wall and is probably from rain coming in at an angle. A shed roof on that side of the building that extends out five or six feet would protect this wall very nicely.

Thank you all for the feedback, I think I agree with the shed roof idea, the plaster was mixed by college students without direction, and it eroded heavily away on the sides of the building witch happened to have less overhang than the front and back.

I am having a consultant from MUDSTRAWLOVE in Asheville NC stop by this weekend to help us re-image a game plan to protect this cob house and treat it with some good respect.

I wonder how horse manure differs from cow, is it more adhesive and binds with sand and clay better?

Jonathan Frame wrote:I wonder how horse manure differs from cow, is it more adhesive and binds with sand and clay better?

It is still full of fibers--they are REALLY similar in size to the chopped fiberglass used to reinforce concrete...

Dan Chiras wrote:Cow dung can be added to earthen plaster, but horse manure is generally better. That said, I don't think manure is going to make the plaster any more resistant to rain, especially driving rains. I see from the photos that there is considerable erosion of the earthen plaster. I would recommend a finish coat of lime-sand plaster. We describe this technique in our book, The Natural Plaster Book. Lime-sand plaster turns to limestone over time and makes a really weather proof exterior plaster.

Dan are you familiar with the proportion of adding animal manures to clay and sand plasters? Will this new texture effect adding a weather proof lime-sand plaster finish? I am motivated to experiment using animal manure, and fortunately we have two horses on site to use manure from, I also wanted to pick your brain about using whey in plasters as they sit overnight to ferment, have you heard of this technique or had any experience with this method? Thank you for your input about both the manure and finish

Jonathan,

I have never used whey in a plaster...so can't comment. I wanted to share something that a friend of mine from New Mexico taught me. He learned this technique from Pueblo Indians...I've never tried it, but I did want to share it with you. They apparently add cactus juice, that is, the gooey stuff inside cacti and succulents, to finish plasters...and according to them, it helps create a water proof plaster. I've never tried it, but it is interesting.

I would experiment with adding lime to an earthen plaster to create a more water resistant outer layer, although, the shed roof will give you bomb proof protection.

Hi Jonathan, et al,

Sorry I am getting late to all of this...

First on your roof...I have to agree with Scott's observation and Dan recommendation. If the structure was a tad shorter 600 mm (~2') would be the bare minimum for a overhang...this structure needs some help there and/or a more water "resistant" (not waterproof) plaster, and/or an Engawa 縁側, (images can be found here)which will enhance the esthetics, add more space and protect the structure and its foundation.

Now I have used several forms of ruminant ordour in the past 40 years from building and restoring Pueblo, Zuni, Hopi, and Deni architecture. Dan is dead on that Horse ordour is superior in many ways to that of bovine, yet in these two ruminate it is more the botanicals the feed on than anything. It is not only the plant fiber that get processed into a more uniform length but also the enzymes that are added, that due indeed aid in the repulsion of moisture. Cactus juice is excellent additive for aiding in water resistance, but not available in all areas though almost any big pad variety after fermentation will yield the adhesive, "dust proofing" effect to the finish. The "pectin" active ingredient in cactus juice) can also enhance lime finishes as well.

Whey is common additive, yet I am not fond of it as the proteins in it can contribute to mold. Casein however is a primary ingredient in many traditional finishes that are often augmented with lime (think "milk paint".)

Regards,

j

Jay C. White Cloud wrote: The "pectin" active ingredient in cactus juice) can also enhance lime finishes as well.

Whey is common additive, yet I am not fond of it as the proteins in it can contribute to mold. Casein however is a primary ingredient in many traditional finishes that are often augmented with lime (think "milk paint".)

Regards,

j

Thank you all for this insightful feedback, I have some experimenting to do and I am so excited, there is no cactus to harvest around here, I would like to try mixing strait pectin in with these upcoming test plasters for this cob house and see how a new lime plaster will respond with horse manure + pectin extract, Hopefully the walls will still breath yet be nice and weather resistant when the final product has been complete, I am meeting with a consultant tomorrow and will report back with new details after. Thank all you again who took the time to post and share with me and each other.

Plug to http://mudstrawlove.com/index.shtml who will be consulting and giving a workshop for us here at Warren Wilson College in Swannanoa North Carolina for helping us lime plaster our cob house,

Also we may be Hosting a talk and workshop with the restoration agriculture man himself, Mark Shepard (http://www.forestag.com/) February 2015 and will post on the proper forum about this in future moments for folks interested in participating

Cow dung is good as an adhesive in small quantities -the clay plaster stick better to the surface. In larger quantities it hardens the plaster and when you add a lot of it, it even makes plaster water resistant (but not hydrophobic). If you want to make it hydrophobic, I would recommend using superhydrophobic nanopenetration for mineral faccades. It keeps the surface dry and permeable to thewater vapor, too.