Waterproof , beeproof cob, Help!

We are making a lovely cob earthship here at Growing futures kenya... We are finally beginning to finish at least some parts of our cob earthship. We aren't quite sure what to do to seal our walls. We also don't have access to all the resources you would in the developing world. We want to have an affordable, local option that our neighbors could use if they were so inclined. I know it is supposed to breath. Are there paints that are ok? what kind of oils can be used? could we use cheaper vegetable cooking oil? coconut oil? We have bees that like to burrow in the clay and wasps that build their nest with the mud. Is there some covering that would keep them out? you can see a video tour of some of the art going up on our walls at http://growingfutureskenya.blogspot.com/2014/09/cobship-video.html webpage I can't figure out how to embed the video or upload pictures

Hello, I have a couple of questions before offing some suggestions -

What's going happening with your roofing? You should have an adequate overhang to prevent water from hitting or running down your cob.

And how is your stem wall? Cob should be off of the wet ground a few feet to prevent splash-back from heavy rains. Great hat and boots is the construction saying that applies to cob, avoid water issues instead of waterproofing.
If your area gets hurricanes or other major storms then you may want to consider something physical just to cover your building during storms.


Plaster (natural plaster) is what is used on the on the outside/inside of adobe brick and the walls of cob, however it is not waterproof. It does offer some protection, but will not stand up to water being sprayed on it. Here is a google search for Natural Plaster recipes - https://www.google.com/?gws_rd=ssl#q=natural+plaster+recipes and I would use the Search Tool here as many great tips have been posted over the years. You can waterproof a plaster but then your walls would not be breathing, as you pointed out. And it sounds like you already know why that is a very bad thing.

Regarding your bees/wasps: I'm not sure what you may have access to, but here's what I might try -
For myself I would try aroma therapy - experiment with whatever herb you have in your region that has a strong smell, like peppermint in my area. You can add this to your external plaster, and even spray a mist of it on the roof eves. Make a batch of peppermint essential oil, other oil and water in a spray bottle, and reapply as needed. Or try using vinegar, in another experiment - you may need to treat your cob with this once a week or more during the bee season to discourage them from your cob. The wormwood plant is suppose to repel wasps, you may have this in your area and can use it instead of peppermint. You could try grinding up onions, garlic plus water and a bit of oil, then strain and spray this - but I have to warn you this may just make you hungry and not repel anything.

Also hang several bee traps around the building to help lower the numbers making it to the walls. You can easily keep bees away by slicing cucumbers and placing them around, I don't know why this works but it does.

Good luck ~

I've embedded the video for you below.

Thank you! How do I embed it? My house is up on tires and has a wide-ish roof unfortunately we get some horizontal rain. If only a small section of one side that needs more protection, the rest is under the bathroom roof on one side and the "garage" on the other. If it had cement plaster on only one side would that be enough for it to breath? I am a total newbie and really appreciate your help. I will try some of our local stinky herbs. Bees aren't so much of a problem once it is hard and dry but we wake up every morning to about three bumble bees half the size of your thumb buzzing around! Once we get the screens in this won't be such a problem... Building a house is such a process!

Hi Evelyn,

To embed a youtube vid - At youtube.com I click on Share - then Embed - and then copy the link they provide. At Permies click on the Youtube button and paste your embed url you just copied.
If your watching the video from an embeded location other than YouTube - in the lower right-hand corner of the vid box you can mouse over and find the YouTube link, click on it to be taken to youtube and load that video - from there you can get the embed link. At least this is how it's worked for me in the past, give it a try and if you have any trouble let me know. Edit: For others having trouble with using Permies - If you will scroll down in the Forms Index to tinkering with this site there are posts in there on How-To use Permies website, just use the Search This Forum.... at the top to find lots of helpful info.

On waterproofing your cob - first off you will find a lot of options containing some scary chemicals for waterproofing which I cannot recommend, and do suggest you avoid. However, there are natural alternatives you can do to that wall which needs some extra protection. You will have to consider the combination of options that will work best for you in your area.

Here is a quote from a website that covers all things plaster and cob very well -

WATER RESISTANCE for Cob - In order to make earthen plasters and paints more water resistant, several strategies may be used. Binders like linseed, walnut, palm, or tongue oil, or sodium silicate (aka potassium silicate, aka waterglass) may be painted on final finish surfaces, and/or added in small amounts to the entire mix of one or more layers. Also, burnishing with steel trowels or smooth stones can mechanically align and compress the surface to close up pores and slow down absorption. Both of these strategies can be combined to create a burnished and stabilized surface that will likely out perform most anything else. Tadelakt is an ancient lime plastering method that combines the chemical stabilization of lime with thorough burnishing, as well as an oil/soap treatment to the final surface that seals all pores. Such a surface, if properly maintained, can remain totally waterproof indefinitely. Other similar methods exist that use only clay binders and linseed oil in many layers to build up a waterproof ‘linoleum.’ However, these methods are arguably out performed by the application of a shingled covering like wood, ceramic, or rock. The addition of these extra surface materials takes more time but is longer-lasting with less maintenance needed. Earthen materials can also be compressed to such an extent that they become nearly waterproof. Compressed earth blocks, for example, can resist rain on the vertical surface for a great number of years before eroding to the point that they even show wear. Depending on the amount of water exposure, it may take many decades before water would cause them to fail structurally. http://www.onecommunityglobal.org/plaster/

I would add that in extreme climates with lots of exposure they built with rock - so if you do have any local hard material (low rot woods or stone) this may be your answer for that exposed wall.


Bees - is there a way you can temporarily cover your windows? Maybe loose screening, shade screen or other inexpensive, thin fabric. . . . any deterrent will help your situation until you can finish things up properly. And you will then know of alternatives to suggest to others following you in their own cob buildings.

Building and Maintaining a house is huge!
Remember to put in things that make you smile, as well as peaceful elements and/or places, as I see in your video you've been doing. Remember to laugh about it all. . . . your joy and sanity through the 'process' is the most important thing IMHO

Do you have access to Lime (Quicklime, Type-S, or Natural Hydraulic Lime)? Tadelackt is an extraordinarily time consuming process. You will need many, many hands.

p.s. Cool video. Just out of curiosity, what fiber are you using in your cob?

Thank you so much for the tech help and reference to the how to!!! Also palm oil is something affordable and available, so much helpfulness It is kind of sad because people in my area are not very employed and almost every big rain one of our neighbors houses falls down ($$!) and their walls disintegrate. We just had a big rain and it sucks to see your neighbors loose their house (then build it again the same). Hopefully our experimenting will start to come together and we can make a picture info book for our neighbors about some low to no cost improvements (used cooking oil on the walls). I really appreciate the suggestions because I don’t have all the time, electricity, internet to search myself.
Because of the difficulty ($$$ and rats would eat it)of sealing the whole house as it is under construction we shelter under a mosquito net which keeps most of the unpleasenties at bay (thank you mom).
I don’t know about lime, I would have to send Jay on a mission to find out (if you want something you have to hope between many, many small shops to try to find something and you don’t always know what they are calling it here. As a white woman I can’t go because the price will be crazy high. Something like palm oil is applicable for our area and budget.
We are using grass. The first batches are rather dubious because the grass was thin and leafy. We have advanced to a type of grass that has crazy hard stems. Other possibilities for our area would be sisal which is relatively abundant. Do you know if you can use coconut coir? If so that would be another abundant material. We also mixed in cow manure because our neighbor has cows and it is readily available.
We have also been planting passion so one day the area will be under passion trellises. We really enjoy ourselves and hope one day (given the country doesn't blow up) to have students, woofers, and people that care can come and share good energy, ideas and FOOD!

The passion trellises are also going to be our wind block to keep the horizontal rain off our wall but passion doesn't grow in a day!

Yes, you can use coconut coir.... I'm glad to hear you are finding materials that will work in your area, that's wonderful!
I'm not sure how much you know or don't know - so just ignore any of the following you already know about *grin*

You can also add sticks, twigs, animal hair and a little dung to your mix. Dryer is better, even though it will be moistened again in the mixing and applying stages; just as in adding straw instead of green grasses.
Here's a quick quote as to why {A: When grass is harvested to make hay for animal feed, it is cut when the plant is still green and the seed heads are mostly not mature. This maximizes the nitrogen in the plant, which makes it most nutritious for the animals that eat it. Unfortunately, this same nutrition is highly attractive to bacteria, fungus and other micro-organisms which will break down the hay when they get a chance, causing it to rot when it gets wet. In contrast, straw is the stalks of mature grains, left behind as a by-product when the grain is harvested. Straw is made mainly of cellulose and lignin, the same compounds that make up wood, with very little available nitrogen, because the nitrogen has almost all been deposited in the mature seeds. This makes straw much more rot-resistant than hay.} Quote taken from one of my favorite websites http://www.greenhomebuilding.com/index.htm

The original style of Tudor was created because people wanted to build faster and increase the volume of building material they had to use - so they added anything available, laying around at the time into the walls. They used a looser cob mix and therefore had to use wood for framing, but they had wood so no problem (think pole building construction). They added dung to make the mix stickier. This is Tudor, and it is a bit faster building style than solid thicker cob loaf style (I mention it just in case it may help your situation, but it does require some framing and I don't know how your area is set for wood). Now days some people call this style of building - slip straw, light clay straw or light clay infill. Read more about it here: http://greenbuildingelements.com/2013/11/23/intro-to-light-clay-infill/

Here are some other materials you can add to cob (if you have them in your area) and quotes about materials -

planer shavings, saw dust, sticks or wood shavings/chips. Horse or cow poo. Any kind of natural fiber like cotton, jute, flax, ramie, sisal, hemp, coir (coconut) or dissolved paper. Mineral fibers would do it too.

longer fibers are as a general rule, desirable because they provide tensile strength to the mix. Sand (or other aggregates) provide load strength.. Take a handful of sand and crush it, it resists, but pull that handful apart and it shows no resistance whatsoever.. Do the same with a handful of straw (fiber), very little resistance to crushing but difficult to pull apart. Generally speaking, the longer the fiber, the better it's woven into the wall (whatever thing you're making), the more tensile strength they provide. As I said before though, it becomes less critical if you're building small things, like benches and so on.

As to proportions, that all depends too. What do you want it to do? Where is (this particular) mix located? Questions like that.
When I'm building arches and larger overhangs, I add LOTS of straw to the mix, though when I'm building near a stove I'll use very little straw but add more sand. Is the thing your building going to experience a lot of downward loading, or will it be pulled in multiple directions?

There IS NO one-true-mix.. You've got to fool with the stuff and see how YOUR clay does with YOUR sand(aggregate) and YOUR straw (fiber). You may find that your local soils need no added sand for a good every-day cob. You may find that the kind and amount of roots in your soils make up for the lack of local straw. No way to know without trying. So make tests with different mixes, let them dry out and test each one to destruction. Don't be afraid to try crazy shit, you may be surprised at the results.

I have time constraints, so I like to use quotes and links to get answers out fast, however I hope it doesn't come across confusing in the process and I hope this helps give you the answers you need. . . . just post back should you have more questions.

Here is some important information on earthen-wall plastering by Andrew Morison at http://www.strawbale.com/too-many-plaster-failures/

Failure #1: Mixing earthen and lime plasters on a wall surface. This is perhaps the most common mistake that I see over and over again. People choosing to use earthen plaster for the scratch and brown coats and a final, “durability coat” of lime. The problem here is that what you have is stronger plaster over weaker plaster when in reality, you want it the other way around: weaker plaster over stronger plaster.

If you consider all plaster work over the last say…thousand years, one thing holds true no matter what material you use. The second coat has more sand in it than the first coat and the third has more than the second. That makes the coats “weaker” as they move away from the wall. This is important because plaster moves, as do homes. If the weaker plaster beneath a strong lime finish coat can move more than the finish coat, you will ultimately get delamination between the two coats which will lead to eventual plaster failure. By laying weaker plaster over a stronger finish coat, it will always be able to move at least as much as the coat beneath it. This keeps the plasters well bonded and eliminates the high risks seen in the opposite application. Cracked cement plaster.

Failure #2: Trapping moisture in the wall. There are two main ways to create this problem. The first is to use a plaster than does not breathe well. For some reason, the use of cement in plaster is still celebrated by some builders. I do not understand this at all. We know that cement based plasters don’t breathe well and we know they are more prone to cracking than lime or earthen plasters. Sure they are stronger, but who cares when they will eventually cause your walls to rot. DO NOT USE CEMENT BASED PLASTERS on a bale home. That is as easy a fix as any.

The second way that moisture gets trapped in a wall is something I see all the time. People decide to use earthen plaster on the home’s interior and lime (or even worse: cement) on the exterior. Those materials all have a different rate of permeation. Let’s consider the most common application scenario: earthen on the interior and lime on the exterior. In any given hour, the earthen plaster will allow 10 units of moisture to enter the wall. During that same hour, the lime will allow 7 or 8 units to exit the wall. The remaining 2-3 units are stuck in the wall and will continue to build up in the straw, leading to moisture trapping issues which are the cause of bale decay.

I very often hear people complain about lime plaster being a bad choice because “they have heard” lime will cause rot in the bales. NO, THAT IS NOT TRUE. What is causing the rot is the overloading of moisture in the wall due to the uneven plaster moisture rates. Yes, there will be rot behind a plaster coat made of lime in this situation, but the lime is not to blame, it is the combination of materials that were used.

To prevent this problem you can either use the same material on both sides of the wall, or you can build up the interior coat to slow down the rate of movement through the wall. This is my favorite option. In the same example, we could simply build the interior earthen coat to 2” and leave the exterior lime coat at 1 1/4”. The added thickness on the interior will slow down the moisture movement through the wall such that the lime can release as much as the earthen will allow to enter in the same time period. Simple fix.

You have all been so helpful thank you so much. I want you to know we are starting a campaign to start a compost business so farmers can have access to fertilizer. The business is also a platform for us to share sustainable agriculture practices we are developing on our demonstration farm. Permies is a group of people who care and I assume you know some other people who care. We really need some help getting our name out because we are doing some really great work. If you can please, please share our campaign we would be very grateful and I will pay you back in beautiful art and increasing food security and fighting desertification. You can find our campaign here