Cob Durability - Case Study in cool, damp winters. Victoria B.C.

I was present when the little cob garden shed pictured below was constructed. It is 12 years old and has suffered some very predictable weather related damage. It's in a community garden not far from the ocean in Victoria on Vancouver Island. Our winters are rainy and damp.


The builders of this structure were volunteers led by employees of a community project meant to demonstrate sustainable living. It's a well funded organization so none of the problems stem from not having adequate resources. They are all the result of poor planning , lack of knowledge and most importantly, an unwillingness to accept help from outside their exclusive clique.

I encounterd the construction crew in the early stages when several key errors were made.

1. The foundations for the protruding cob which supports the wooden benches were very shallow and inadequate.
This caused the cracking which is evident in the second photo.

2. The benches were set on an angle sloping toward the walls. A rain trap. This caused erosion at that spot. The benches were reset a few years afterward.

3. The roof membrane is plastic and will wear out long before it should. The beautiful green roof will have to be completely dismantled.

4. This is the worst mistake. The roof overhang is too small. It takes only a light breeze to blow drips from the roof onto the benches and lower walls. This has caused weathering of the cob on the windward face. The problem of bench slope and the cracking are made worse by regular soaking.

They used a really good mix for this building with great detail to proportions and to thurough incorporation of ingredients. The plastering was also done right. About 70% of the building is protected from water and these areas are in excellent condition. Only areas exposed to liquid water show evidence of wear or erosion. The entire building is exposed to high humidity for 6 months at a time. It is unheated. From this we can see that liquid water is the culprit here. High humidity for extended periods has caused no damage.

I offered to help this project to succeed. I pointed out the problems and offered to correct them free of charge. The girl in charge rebuffed all of my attempts to intervene.

I offered to take my truck to the beach and bring back thicker, longer rafters so that a proper overhang could be achieved. I offered stone to make foundations for the bench buttresses. And I offered to pick up some pond liner for the green roof. No, to all of it. Even her boss said there was nothing he could do about her stubbornness. So everything you see in these pictures is a direct result of her decisions.

I had had previous dealings with the organization. I gave them lots of plants from my demolition projects and had supplied lumber for various projects. The carpeting in their office was from me. But none of that mattered. Nobody was allowed to have any influence on this pet project.

So, I guess the moral of the story is this. If you are inexperienced and somebody with vast experience offers free advice and help, take it. Even if you are confident that you're headed down the right road, hear them out. Even if it comes from your know-it-all brother in law, take the help. You can always check the internet and tell yourself you learned it there.

Back to the photos----- The pink areas around the benches have been fixed up at least twice. Benches have been reset to drain water. Cob arm rests of benches have been re-plastered numerous times and are overdue for more. The benches are seldom used. Water did all of this. It's not an abraision issue.

The final photo is of a portion of the building that is protected from dripping water. Good as the day it was made.

The first two photos below show more of the damage to areas not protected by a decent overhang. A combination of frost heaving and water erosion has led to this.
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The last photo shows an area that has a good overhang out of the worst of the wind. This section looks the same as it did 12 years ago. The rub marks and little seed pods that were visible on the surface 12 years ago are still there. When I rub my hand on it there's no dust and no loose sand. My best guess is that this portion of the building could go on for 50 or more years without requiring plaster. This is far less maintainance than you'd expect with wood, vinyl or stucco siding.

Cob doesn't like to have water running over it. A cob building can last for 5 years or for hundreds of years. Decisions made early on are the biggest factor in determining maintainance requirements and long term durability.

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I have shown this building to two of my brothers and to several friends when explaining what cob is and how it works. I always point out the positives and how most of the building looks like it will last 100 years. But most of them can't get past the water damage. They say things like, "It's way too wet in Victoria for mud houses" or "I don't think that will last". It's too bad. What was built as a demonstration project to showcase sustainable building has turned into a cautionary tale. To me the lesson is simple --- Water is your enemy. Don't let it run down cob walls.--- But to the majority of visitors to the park/garden this little building stands as a warning that cob is not durable and requires constant maintenance.

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I intend to offer my services to completely refurbish the shed. It will be conditional on doing everything right. That means doing it exactly as I advised 12 years ago when I was only vaugely familiar with cob.The roof will need to come off and be rebuilt with more overhang. Pond liner will be used. The buttresses should be removed and replaced by wooden braces hidden beneath the benches. And the whole thing needs matching plaster. I'll want to affix a sign of my design explaining what cob is along with a brief history of the building and it's good and bad points.

It will be interesting to see what happens.

It's a shame the project manager wasn't more receptive to your input. And you are absolutely correct about the negative effect buildings such as this one can have. About three months ago I fell in love with cob construction and it's seemingly infinite, beautiful, potential. However, I quickly started to shy away from this technique as I was shown several poor cob examples such as this one. Being new to the entire concept, I didn't have an understanding of what was actually going on or why (and I barely do now). My experience makes me wonder if this project could be used to show the effects of poor design or construction while supporting the reasoning behind the currently acceptable techniques. I also believe deconstruction of a structure has the potential to reveal opportunities for improvements in design, materials and construction even if the original builder adhered to the conventional wisdom.

I hope you consider a video chronicle of the rebuild. A detailed article with lots of photographs would also be nice.

I will definately document every step if I get the go ahead. This is an "I WAS RIGHT" oportunity that my ego will not allow me to pass up. You may even see video footage of the "I WAS RIGHT DANCE" a glorious display of self confidance and lack of a normal filter. I've been harping on this every time I drive past the garden for the past 12 years. If all goes as I hope, you'll hear me crowing like a rooster as I anoint myself as our "DON'T BE DUMB" watch dog. I've gotten myself into trouble on here several times simply because I'm a conaseur of train wrecks. This will be a perfect platform for my pontification. --- I can't see how I would get myself deleted if I'm mocking my own project.

Speaking of water damage, this is what I did today. My friend bought this house from an idiot who piled dirt right over the concrete and onto the wooden shingles.

Flag stone was laid over most of the yard and the side of the house was the easiest place to dump soil that was excavated.
After 3 years there is quite a bit of localized damage. I'm digging to 6 inches below the wood, then adding some rubble rock.

I have to question where things went wrong in his upbringing. How did he get to be 50 years old and not accidentally learn that wood rots if you cover it with mud? Has he never noticed the rain on the Pacific coast ?

Good stuff Dale!

In your experience have you seen any sort of plaster or coating that will make cob more resistant to running water erosion? I ask because I have seen a few pictures of cob hot tubs and was wondering how in the world that would hold up. I had an idea for creating a cob waterfall for my eventual pond, not Niagara type flow, but a decent trickle to keep 02 in the water. Just a thought I had but I am not to keen on having to redo the project every few years. I haven’t read "Hand Sculpted House" yet, got 2 more books to finish first, so most of my info has been from the net.

I know that lime coatings are far better than bare cob. But given an adequate overhang and proper grading it should be possible to build from talc powder. Haven't checked what the Hot Tub crowd are doing. I intend to insert a fiberglass tub into cob. Plenty of older tubs available for free since motors and jets fail. I will glass over those things since I just want hot water without the undertow.

Thanks for this reminder Dale.
This is why I tell people NOT to build cob benches as demonstration projects. I've turned down several offers to build them and ALWAYS discourage others on this.
Cob benches get forgotten once they're built. Roofs are often neglected or not built at all. People plop their stuff down and break off a corner, or carve their initials into the plaster.
Without constant maintenance, a cob bench demo project can, in a very short time look like a demonstration of what NOT to do.
Unless you, the builder, live close to the site and WILL repair the thing, don't build it in the first place!

Donkey is the builder of the most interesting RMH on the internet.

I left a message concerning the repairs. It's a non-profit, so who knows how long it takes to come to a decision ? Time will tell.

Dale Hodgins wrote:I know that lime coatings are far better than bare cob. But given an adequate overhang and proper grading it should be possible to build from talc powder. Haven't checked what the Hot Tub crowd are doing. I intend to insert a fiberglass tub into cob. Plenty of older tubs available for free since motors and jets fail. I will glass over those things since I just want hot water without the undertow.

I wonder if tadelakt would work satisfactory for tubs? I know that it is used for showers and sinks.

Tadelakt has been used for water tanks, why not a hot tub??

Kirk Mobert wrote:Thanks for this reminder Dale.
This is why I tell people NOT to build cob benches as demonstration projects. I've turned down several offers to build them and ALWAYS discourage others on this.
Cob benches get forgotten once they're built. Roofs are often neglected or not built at all. People plop their stuff down and break off a corner, or carve their initials into the plaster.
Without constant maintenance, a cob bench demo project can, in a very short time look like a demonstration of what NOT to do.
Unless you, the builder, live close to the site and WILL repair the thing, don't build it in the first place!

Whenever you have problems convincing building officials or anyone else about the merits of various green building methods, it's important to remember that some well meaning idiot may have gotten to them first. It may have been a direct contact thing which is good since there is an individual to blame for any failure to explain the positive aspects of the technology. Usually, we never meet the buffoon responsible for screwing up a building project. We simply see the result and if we're not familiar with the whole idea of the thing, it can appear that the concept or technology is at fault, when in fact it was a poorly executed example of a perfectly sound idea. SAY ALL OF THAT TEN TIMES FAST

They haven't called. The organization who built the thing isn't sure who is to maintain it, which reinforces Kirk's point about the benches.

I went to the little building again today. Deterioration has accelerated. We've had lots of driving rain and they've planted cabbages right up to the building. Rain hits the cabbages and splashes onto the walls. Some of the worst cracking has been patched with what appears to be tile grout. It's very hard and glassy and chocolate brown. BUT THERE'S GOOD NEWS.
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While walking back to my vehicle, I passed Victoria's only other prominent cob structure, which is a big bench with salmon, starfish and other sea life beautifully moulded into it. This one is only about 6 years old but in far, far worse shape than the shed. I always drive this route and hadn't taken notice of the bench since I watched it go up. For some reason, I thought it was finished in ferro cement. The thing is eroding badly along the wide,flat head rest, rocks and glass have come out. The entire structure is saturated. It should survive until spring, but it would never last another 3 years. It was a real thing of beauty so I hope the details survive the winter.

It's two feet from the sidewalk and belongs to the largest volunteer group in the area. Two minutes after meeting the lady in charge, she agreed to have me fix it right. All rain trapping embellishments will be removed or altered, some slopes will be changed and when it's done, It will be given several layers of lime wash. After that, the plan is to have it decorated differently every year with coloured lime washes, so that it will always have a fresh coat. I will remain in charge of prescribing maintenance. Labourers will be provided. I may go so far as to paint my business name onto it. It's in a very busy area and we don't allow billboards here. A brightly coloured add, right on Menzies St. aaaah.

Most importantly, no other person will have any input on design matters. It will be my project, an important step in my plan to usurp all failing leaders of Victoria's faltering green building movement and take over all failed projects. Taking over these projects is an important first step as I work toward branding myself as a green builder who understands his materials. Being so close to the shed, I'm bound to find out who is in charge of that. I don't want to kick anyone to the curb. I'd rather have them join in ongoing maintenance and learn something in the process. I'm very keen to retain control for another reason. Every so often, the local paper does a story on this sort of thing. Any positive media buzz will now be directed toward, “Dale of Victoria Camping Bus and Charters. That guy who hauls people to green building events.”

There are some good sections on Graeme North's website (look under 'white papers') about both building code, and primary weather protection. He's a NZ architect and instrumental in their process of creating building code for earthen building (and I believe they also looked at straw bale) in New Zealand.

ecodesign.co.nz

"A good hat and a good pair of boots" - a roof with sufficient overhang to keep weather off the walls, and well-drained and stable foundations that prevent both splash and ground damp - is the entire secret to cob buildings that last for centuries instead of returning to the mud from which they came.

Other good resources for time-tested cob technique:
Mike Wye out of the UK:
historic restoration specialist, supplies materials like lime plasters & cob block in the UK, also lots of great articles on repairs, moisture management, etc.
www.mikewye.co.uk


From Cob Cottage Company, a compendium from many sources: Earth Building and the Cob revival: a Reader www.cobcottage.com

World Heritage Organization Earthen Building Project: http://whc.unesco.org/en/earthen-architecture/

I've heard lots of good things about silicate paints, also known as waterglass.

" A waterborne, single component inorganic coating material for masonry wall surfaces. Silicate Mineral Paint penetrates the substrate and cures by an irreversible chemical bonding process, forming a microcrystalline structure which cannot peel or blister."

Its suitable for porous and semi-porous surfaces, and remains breathable. I plan on using it over my exterior lime plaster and any cob/adobe/clay plaster I do. The brand I've heard about is called Keim.

Erica Wisner wrote:Other good resources for time-tested cob technique:
Mike Wye out of the UK:
historic restoration specialist, supplies materials like lime plasters & cob block in the UK, also lots of great articles on repairs, moisture management, etc.
www.mikewye.co.uk


From Cob Cottage Company, a compendium from many sources: Earth Building and the Cob revival: a Reader www.cobcottage.com

World Heritage Organization Earthen Building Project: http://whc.unesco.org/en/earthen-architecture/

Thanks Erica for your advice on both this and the cob bench that we talked about last night. I'll soon post photos of the well preserved specimen.The light wash soaking isn't something I had thought of but it makes sense. What do you think of the paints that Peter mentions ?

Bump.

Would love an update please

Sam Boisseau wrote:Bump.

Would love an update please

Still haven't heard from anybody in charge. I did repair work on a bench. It looked great at first, but some lime wash came off during the winter. Exposed cob does not work in my area.

Bump.

Updates please?

Could you let me know where I could see the buildings? If you don't want to say here, feel free to PM me.

The shed is at the corner of Menzies and Michigan, in James Bay. Slated for demolition when the garden moves.

The bench that I repaired, is gone. Rain killed it.

The best cob structure in the city is failing. Photos below. The last photo is a bench in a private yard that they are getting rid of. That's pretty much every cob structure that I know about in Victoria. All gone or going soon. All have suffered from water damage.

Thank you for the update.

Sad to hear that the structures aren't holding up well. Hopefully I can make it to see the one in James Bay before it vanishes.

A couple of weekends ago I went to see the cob buildings at eco-sense. It's very interesting to see the difference between the two styles of building. The Eco-sense people built pretty good foundations and HUGE overhang on their roofs, unlike the examples you give in this post with the small roofs. Very interesting to see how well the eco-sense buildings are standing up to our weather.

The shed is gone now. The entire garden is being redeveloped. It was on borrowed land. The final cob structure on public display, is deteriorating quickly.

Cob in this climate, needs a good roof. To do otherwise, is to turn the project into raw material for one of my cautionary tales.