materials

Cob is a very eco-friendly and cheap building material, as I found out on Wednesday when I spoke to cob building expert, Kate Edwards. As with straw bales, I was surprised to find out that cob buildings are very long lasting and can be more than one storey tall - indeed, there is an example of a ten storey building that is over a thousands years old!

One of the nice things about cob is that for most people, they can source the material locally, from their own foundations. I chatted to Kate about that, and about the process of building cob buildings:

And then Kate gave me a demonstration, showing me how to insert windows into a cob building, and discussing the merits of the cob pizza oven:

I took a lot of photos, which I’ll post up here later, but in the meantime, here’s my Grand Designs Live photo set.

Stand B130 in the Grand Build section of Grand Designs Live is possibly my favourite part of the entire exhibition. It features companies that build with straw bales, cob, and timber frame makers. I spent quite a bit of time on the stand yesterday, talking to about building out of straw and cob.

Amazonails is a company that offers designs, advice, consultancy and training in the use of straw bales in construction and Sophie walked me through some of the concepts involved. We spoke firstly about how straw bales are a structural building material, which surprised me no end. You can build entirely out of straw bales without needing a wooden frame to hold the building up.

We then talked about how you render the bales, with line on the outside and clay on the inside.

This is an example of the clay render:
And the lime render:
With a lovely example of pargetting, or sculpting in lime plaster:
And finally, how do you build a straw bale wall? It’s actually very simple.

Here are the stakes that hold the bale in place:And essential equipment for tidying up the bales, which apparently get a bit ‘hairy’ when freshly laid, and for sculpting rounded corners:

For me, straw bale building is an exciting idea. It’s very cheap, very easy, incredibly green, and you can do a lot of it yourself. Amazonails do training courses, so you can learn how straw bale building works before embarking on your own project.

One of the fabulous things about Kits and Mortar has been how fast the idea has chimed with so many people. I’ve never started a blog which has prompted so many messages by email and Twitter from people interested in the same subject who wanted to suggest ideas. It has amazed me - after all, Kits and Mortar has only been around for a little over a week! So today’s post comes to you thanks to Jemima, who emailed me this morning about Earthships.

Now, I know what a mothership is, but earthships are new to me. Turns out that they are houses made of local unwanted materials. I’m not going to use the word ‘rubbish’, because that has unfair connotations such as “it stinks, rots away, and is generally bad”; but nor am I going say that they use recycled materials, because that implies that they reuse bricks, blocks, girders, etc. Instead, these houses are made of tires packed with dirt, empty bottles and drinks cans.

The Brighton earthship. Thanks London Permaculture!

The idea was developed by Mike Reynolds, who’s built a couple of hundred of earthship houses in New Mexico, as The Telegraph reports:

The specific advantages of the earthship model are spelt out by Mike Reynolds, who has built about 200 such buildings in the region around Taos, in New Mexico. “An earthship has no utility bills because it solves the issue of internal temperature by means of a highly efficient insulation system,” he says. “Its power comes from solar and wind energy. A catchment system on the roof collects rain and provides all the necessary water, which is recycled four times. It processes its own sewage, which is diverted into a reed bed and provides manure for the garden. And in its construction, it recycles the rubbish we create.”

An earthship is really just a self-sufficient greenhouse with a huge, inbuilt storage heater. On three sides, it is tucked into a bank of earth - ideally, a natural hill - and lined with walls of tyres. The fourth side, the front, which must face south, is all glass. Heat builds up during the day (natural ventilators cool it down if necessary) and the surrounding thermal mass of the earth radiates the heat back at night. In many respects, it provides the solution that the award-winning Hockerton housing project in Nottinghamshire does, but the three-sided insulation of that scheme is made of concrete.

These photos show walls being constructed on a build in New Mexico:

Thanks Mrs Hilksom!

Thanks stereogab!

Of course, once the walls are rendered, they can look quite lovely:

Thanks Josh Russell!

But I’m left feeling very uneasy by some of the ideas promulgated by Earthship.net. Their ideas about using solar and wind energy, catching rain for water supplies, and processing sewerage using read beds are fine, but I’m not yet convinced that using tyres, aluminium cans and glass bottles is actually the best way to reuse these materials.

Firstly, aluminium can be recycled and, in my opinion, should be. Aluminium is a finite resource, and whilst it’s unlikely to run out in our lifetimes, it is going to run out one day. Additionally, refining metals is a more energy-hungry, resource-intensive and polluting process than recycling them. Aluminium is made from bauxite which contains alumina and, according to WasteOnline:

Recycling 1kg of aluminium saves up to 6kg of bauxite, 4kg of chemical products and 14 kWh of electricity.

Recycling aluminium requires only 5% of the energy and produces only 5% of the CO2 emissions as compared with primary production and reduces the waste going to landfill. Aluminium can be recycled indefinitely, as reprocessing does not damage its structure. Aluminium is also the most cost-effective material to recycle.

A recycled aluminium can saves enough energy to run a television for three hours.

If all the aluminium cans in the UK were recycled there would be 14 million fewer full dustbins each year.

If we want to protect the environment, we should be recycling our aluminium cans, not turning them into walls. The earthship fails the environment on aluminium.

What about glass? Well, again, glass is easy to recycle and doing so saves the use of raw materials, reduces the energy required to create glass, and saves C02. Stats again from WasteOnline:

For every tonne of recycled glass used, 1.2 tonnes of raw materials are preserved.

If recycled glass is used to make new bottles and jars, the energy needed in the furnace is greatly reduced. After accounting for the transport and processing needed, 315kg of CO2 is saved per tonne of glass melted.

Sorry, but earthships fail on glass too.

Finally, tyres. It is illegal to dump tyres in landfill sites in the EU, and burning them produces pollution, but they can also be recycled by processes such as retreading. Otherwise, the tyre can be dismantled, the metal rims recycled separately and the rubber used for other purposes, or ground:

Grinding is the most widespread materials recovery process in the UK. In 1999 it is estimated that 83,000 tonnes of tyre were granulated. This process produces a range of crumb sizes through the progressive size reduction process with the energy used to break up tyres increasing as the particle size decreases. Crumb is used in sports and play surfaces, brake linings, landscaping mulch, carpet underlay, absorbents for wastes and shoe soles. Crumb can also be recycled in road asphalt. Rubberised asphalt can increase road elasticity, temperature range and resistance to oxidation, which can result in fewer ruts, potholes and cracks in the surface. In 2000 a crumb road was laid near Battle in East Sussex.

Some crumb can be used in formulations with virgin rubber, but this is less than 5% of the total. Salford University in conjunction with Pirelli and Corus has produced a crumb 0.4mm in diameter, small enough to be recycled in tyres. Pirelli plans to increase the 5% rubber crumb content currently used in manufacture to 20% in 2006. Corus hopes to use the steel innards for smelting. For contact details of UK based companies involved in rubber crumbing and other recovery methods visit the Used Tyre Working Group website: www.tyredisposal.co.uk

There are other ways to recycle tyres, but most - 40% - are not recycled but instead used in a landfill, stockpiled or illegally disposed of.

So perhaps using tyres in building may not be a bad alternative, although there’s also the question of whether they release pollutants into the environment. I don’t have time to research that one right now, so it’s going to have to remain an open question.

Equally unanswered is the question of whether tyres rammed with earth actually make a good building material. I don’t have the expertise to say, but I wouldn’t like my house made of them.

I’m also disturbed and saddened by the anti-wood propaganda on the Earthship.net site:

We have built out of wood for centuries. Wood is organic and biodegradable. It goes away. So we have developed various poisonous chemical products to paint on it and make it last. This, plus the fact that wood is light and porous, makes it a very unsatisfactory building materials. This is not to mention the fact that trees are our source of oxygen. For building housing that lasts without chemicals we should look around for materials that have durability as an inherent quality rather than trying to paint on durability. Wood is definitely a good materials for cabinet doors and ceilings where mass is nto a factor and where it protected so it will not rot, but the basic massive structure of buildings should be a natural resource that is inherently massive and durable by its own nature.

Sadly, this is rubbish. Wood can be very durable and strong indeed. Oak, for example, strengthens as it ages, and is not prone to decay. That’s why our ancestors built so much with it. Indeed, as long as wood is sourced from local sustainable forests, it is very environmentally friendly.

A couple of hundred years ago, ship builders across the UK were planting trees as part of their plan to ensure the Royal Navy never went short of timber for its ships. Of course, metal ships came along and the wood wasn’t needed, but it is perfectly possible to manage timber sources ethically and ensure that we have a steady supply of good wood. Indeed, using wood from managed forests could even result in more trees being planted, something that should please even the greenest of people.

To say that cutting down trees is bad, that wood makes a poor building material, and “goes away” is a naive and blinkered attitude. Equally, to insist that wood preservatives have to be noxious is also ignoring the preservatives available which are environmentally friendly.

Overall, I’m disappointed by the earthship project. It seems to me to have its roots in fantasy instead of reality, and I think it lets the environment down on some key points. Building a green home isn’t just about renewable energy, saving water, and processing sewerage. And green materials are far more complex than just using whatever’s lying about. For every can stuck in a wall, how much extra bauxite has to be dug up to make a new one? For every glass bottle, how much extra sand?

I doubt that our home will be 100% green, because I think that’s an impossible target to attain, but whatever compromises we make, we’ll make them with our eyes open, and we’ll keep our heads out of the clouds.

January 26th’s New Scientist ran an article on E-Crete (p 28 - 29), which is sadly behind a paywall but which I shall do my best to summarise here.

Concrete is a very versatile building material, but it’s not very green. The production process for Portland cement, a key ingredient of concrete, involves heating limestone up to 1400C. This produces half a tonne of CO2 per tonne of cement, with another third of a tonne of CO2, or more, produced by fuel burning, transport, etc.

Not good.

Indeed, it’s estimated that 5 - 8% of global CO2 emissions come from cement production, and demand for concrete is predicted to double over the next decade. The construction industry isn’t the fastest moving industry on the planet, but change is happening.

Enter Australian company, Zeobond, and their more eco-friendly E-Crete, a geopolymer concrete which releases just 10% - 20% of the CO2 from traditional concrete. It’s made by taking silicates and aluminates from fly ash and slag - the waste from power stations and steelworks - and adding an alkali which reacts chemically and produces a long molecule called a geopolymer. This can then act like cement does, binding together any gravel and sand that are introduced. The polymerisation process requires no heating, and produces no CO2, which makes it much greener than traditional concrete.

Whilst geopolymers have been used for the last decade in things like catalytic converters, it’s only recently they’ve started to be used commercially for construction. There have been worries that they set too quickly, making them hard to handle, and are more porous than traditional concrete and so may decay faster. But changes in the production process and rigourous testing suggests that they’re just as strong as concrete. Now geopolymers are being used in construction and engineering, as railway sleepers and in buildings.

Yet it looks like it’s going to be a while longer before we see a wholesale movement to geopolymers as conservative industries like construction are very risk-averse and want to see new materials fully proved before they adopt them. E-Crete’s green credentials might speed up the process, as pressure builds for the industry to change its ways and reduce its carbon footprint.

For me though, I’m excited not just by a concrete that is so green, but also by the fact that it recycles waste from other industrial processes. We need to think a lot more about closing loops, making the waste from one process the raw materials for another.