The Village Alchemy Project will be intermittently uploading and updating our site with useful resources such as this manual for natural building cob care.
Click here to download the Natural Building Mini-Cob Care Manual in .pdf.
text of the document:
NATURAL BUILDING MINI-COB CARE MANUAL
All buildings require regular maintenance. A house that is no longer inhabited quickly begins to deteriorate. When we build ‘things’: benches, houses, furniture etc. we are engaged in building not only the thing itself, but also relationships. These relationships are not only with the other people involved in the process but include the relationship to what has been created. A relationship with out energy going into it will eventually fade away, or worse. What we create needs us or someone to take care of it. If you are constructing anything that is out in the Northwest weather, be it concrete, wood or cob, it will require extra attention. Water ( aka: the universal solvent) can do a lot of damage in a little time if left unchecked.
There are many details to think of when building a structure out of cob. Ideally, good design has taken place either prior or during the construction phase with the notion of longevity in mind. Though, natural building lends itself to intuitive building and is relatively easy to do, it takes years of experience to really become familiar with a material and how it sustains itself in any given environment. For folks with limited experience in construction or natural building there are some simple principles to good building: ‘Good hat and good boots’!Hat: make sure that your project is sufficiently covered with a roof that has large overhangs appropriate for the weather conditions of your site, is well attached and, of course, water proof. When in doubt build a roof! A good roof is the best protection against weather, and it if it is for a bench then you can sit on it all year round! If you are not incorporating a roof (not recommended) make sure you and your builder go over the details so that your project does not invite water into it. Example: for benches (with roofs and without) make sure that the seat slopes away from the back to shed water, there are no concave impressions in horizontal surfaces, mortar between stones is not cracked, landscaping around structure does not touch cob at base, if there is a roof how does rain falling off the roof behave (splash back) etc…Make sure that you have a reliable sealer to make it water proof and the time and commitment to maintain it. That means every summer you will oil and wax it.
Boots: Make sure that what ever you are building is at least a foot above the earth on a material that does not absorb moisture. This prevents moisture from wicking up in to the building, bench or kiosk. It also prevents water from splashing onto the wall or bench. For structures that are to be bermed into a hillside, it is very important to make sure you have designed the drainage behind the structure to deal with a great volume of water and that measures are taken to prevent it from silting up. When you have questions as an experienced builder, or better yet ask a few.
HOW TO MAINTAIN YOUR PROJECT:
An ounce of prevention goes a long way in the cob world. Regularly oiling your cob project is important if it is regularly exposed to water and rain. It’s is important to oil your project when it is thoroughly dry. The thicker the project the longer it takes to dry. Most projects done in May are dry by July or august. Each builder has her own recipe for oiling and waxing cob.
OILING RECIPE
As a preliminary warning Linseed oil is extremely flammable, smoking is bad for you so you shouldn’t do it, let alone while you are working with linseed oil. Any rags used or brushes for this oiling process should be kept away from any flame source and left in a safe and ventilated place to air out after use. Orange oil and turpentine are solvents. If there are surfaces that are painted these fluids will melt the paint off. As good as orange oil smells- do not ingest!!!
- One coat of pure linseed oil (a good slathering!), followed by a coat of 75% linseed oil, 25% turpentine (or orange oil).
- Then a coat of 50% linseed oil and 50% turpentine (or orange oil).
- Then a coat of 25%linseed oil and 75% turpentine (or orange oil).
All coats are brushed on with sufficient time between coats for absorption (6 hours +is ideal, but not totally necessary).
There are a variety of mixes for wax and the following is a simple one: 25% linseed oil and 75% turpentine (or orange oil) that is warmed in a pot (BE VERY CAREFUL) not too hot, just warm to the touch.
In a double boiler melt a pound of beeswax for every gallon of liquid mix. When the wax is melted pour it in to the linseed oil mix that is warm. Take it off the heat and it is ready to go. You can either brush it on the surface or use a rag (usually easier after the wax has set up a bit). What ever is left over can be stored in an container and used the following season.
This wax mix is also good for patching any cracks that might form later on. If you have a lot of cracks to patch- double the beeswax in the recipe.
INDICATIONS OF WATER DAMAGE:
- Cracks
- Plaster peeling off
- Change in color
If your project is showing signs of water damage like those above, protect it from the rain. Throwing a tarp over water damaged cob only increases the water issue by trapping moisture. If the tarp or plastic is in direct contact with the cob it will act like a band-aid in the sense of a band-aid on your finger while you do the dishes. It isn’t a pretty sight! Cob, like skin, needs air. If you need to tarp the structure use sticks or wood or stones or what have you to elevate and create an air space under your tarp or plastic covering. Prolonged moisture in the cob will rot the straw and significantly reduce its tensile strength. For structures with extreme corbels or overhangs this can be very hazardous. Also, if there is a lot of moisture in the cob and a freeze comes to town, you can expect some pretty hefty damage.
Cracks:
Cracks anywhere in a cob structure leave openings for water and life forms to penetrate the structure. Cracks in cob that are 1/8 of an inch or greater are of great concern as they represent serious movement within the cob, ie there may be a structural problem. Cracks that are hairline or just the depth of the plaster can indicate a few issues, ie too much clay in the plaster, plaster over too dry a surface, over troweling, or cob shrinkage. Cracks between different materials are also important to take note of. Anytime you have dissimilar materials that are joined they will expand and contract at different rates. Where wood protrudes out of a cob structure to carry the roof, or where the foundation meets cob, or anything that may be inlayed in to the cob- these are all areas where you can expect to find hairline cracks. This includes concrete caps or cracks between mortar and stone on any surface. If a significant amount of cob is built in a short period of time it could be the result of mass shrinkage, since cob will always shrink. If the crack appears after the structure has already been built and oiled it could mean that there is water getting in and expanding. Usually, these cracks appear in cob structures that have been plastered. If found soon enough filling with a thick mix of beeswax and oil can remedy it for a season. A small or multiple small undetected cracks can result in plaster peeling off. Cracks in a cob project that has been burnished, instead of plastered, could indicate some bigger problem is the cracks are deeper than just the surface. However, in order to protect the project until a more complete examination or time for repair, fill those cracks with the aforementioned thick mix of beeswax and linseed oil.
Plaster peeling off:
Frost heave, water infiltration and poor underside detailing are probably the biggest reasons for plaster peel. Once the cob becomes hydrated due to winter rains and a frost occurs, it swells in that seam between the cob and the plaster and poof, by spring the cob creation in question is shedding these leathery sheets of plaster. Good overhangs and detailing are the primary prevention of water damage combined with consistent and perceptive observation. Correct application of the plaster is crucial for a long lasting plaster. Clay bonds via electrical charge. It is sticky because of electrons! So it is very important if you want a good bond to have a good conductive surface, and that means a wet surface. Before plastering it is vital that the cob surface be wetted down (this is an often overlooked detail, particularly when it comes to repair work). Not soaking wet but moist enough to not evaporate immediately but not so wet that the cob is gooey. It should remain firm to the touch. It is very common to forget, or not see that you are not getting the area right above the foundation wet when misting prior to plaster application. If these areas don’t get sufficiently moist then the bond between the two layers is weak. This area is also prone to splash back, being damaged by human and animal contact so it is more likely to acquire a crack and let water in. When there is a crack in this area it is also more inviting to insects and life that further the degradation of the structure. To repair this type of damage, remove all loose plaster, make a new batch, scrape the exposed cob surface and score to remove all lose material. Wet the surface and reapply a new plaster, then follow the oiling procedure once it all thoroughly dry. Always check the weather before doing major repairs. There is nothing worse than replastering only to have the rain wash it all away.
Change in color:
A change of color can indicate a few things. If a plaster over a cob structure changes color it could mean that the plaster is getting wet from something, a leak somewhere or a drip. Sometimes cob just gets dirty (fancy that!) and you can get soap and water and scrub the surface. Sap from trees, pollution, graffiti etc can all be scrubbed off if the structure has been previously oiled. If not a replastering should be done, if the discoloring has been discovered and resolved. After scrubbing cob it is important to let it dry and then give it an oiling and/or waxing. It is essential that while you are participating in the building process you take the time to learn as much as you can from your local builder as to how your project is constructed and how you must maintain it.
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Written by utopia0rbust
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