Almost one year later…pop can walls!

We started our first pop can wall today.  We decided to make the bond beam form on the front wall out of pop cans, a traditional method according to Michael Reynolds.

We opted for cans because the front wall will be most susceptible to moisture, both from the dirt that will be backfilled to this wall, and from rain and snow that will slide down our slanted windows.

The Eartship books call for a mixture of one part cement and three parts sand.  Because we were working in smaller amounts and having to make a matrix of concrete and metal cans, we decided to screen the sand a second time. Chris built a screen out of 2×6 and leftover stucco wire, which left the resulting sand very find indeed.  We didn’t take picture of this, but by looking at the wall, I see more screening in our future!

Our first dilemma was making a line down the tires that was parrallel to our closest rafter position.  After arguing discussing this problem we decided to run a string line from one end of the building to the other at rafter height, took our 12′ level and made a perpendicular line.  We measured from the level to the tires at many positions and ran a chalk line, marking the line in lumber crayon on the tires, since the chalk line was inadequate for marking.

We used this chalk line to line up the bottom ends of the pop cans which will be inside the bondbeam.  We positioned the can tabs alternating  directions as indicated in the Earthship volumes. This alternation makes plastering (using the tabs as lath) much easier down the road.

It became apparent very quickly that a) pop can contruction is an art not a science and b) while easier physically than tire packing, this job was going to take us all weekend…

But here it is…looks just like in all the pictures! 

Pouring The Concrete Bond Beam

A few days ago was the day and man am I tired!  After months of waiting through winter, we picked yesterday to pour the concrete bond beam on top of the back wall.  We have been preparing for this pour since we started work on the house again in February; screening gravel and sand, building the bond beam form and hauling in the portland cement we needed for the job.

It was an ugly morning.  Rain the night before with heavy winds, and neither the rain nor the wind had completely died down.  We started setting up not really convinced that we would actually start pouring concrete.  Nobody wanted to be the one to cancel the pour, and after a couple of rounds back and forth discussing options the decision was left to me.  Not one to be hasty I deliberated and we got started right away … Fortunately the rain cleared up and we had sunshine with really heavy winds for most of the day.

We decided to mix our own concrete for this job rather than have it delivered from a plant in Kamloops.  I estimated that the pour would require at most 4 cubic yards of concrete and the minimum delivery is approximately 5 yards (concrete is now sold by the cubic metre which is slightly larger than a cubic yard).  So, if we had ordered concrete I would have had to have planned ahead by having additional forms ready for concrete.  Also, due to delivery charges (we are about an hour away from the closest concrete plant), the delivered concrete is that much more expensive if you order a small volume.  Given our desire to save money and our limited ability to plan ahead it seemed a no-brainer to mix our own concrete.

We have mixed lots of concrete on this project and in the past, but never this much at one time.  Our little cement mixer can mix two cubic feet of concrete.  Given that there are 27 cubic feet in a yard, we would need to mix about 60 batches of concrete for this job.  Assuming we could mix a load every ten minutes we would be looking at about ten hours of non-stop work just mixing the concrete, not to mention pouring it onto the forms and leveling.  We quickly decided we needed more manpower on this job …

The first workers we lined up for the job were John (aka John Deere) and  Bob.  Bob actually insists on going by BobCat … I find this really ’70’s, but he packed all of the concrete from the mixer to the forms so whatever name he wants to be called is fine by me!  The cement mixer on the back of the green John Deere tractor is driven by the PTO (power take off) of the tractor, and it can handle about a sixth of a yard per batch.  So, we only had to to do about 20 batches of concrete.  The tractor was parked by the sand/gravel pile all day, and the mixer ran for most of the day spinning the mixer.  When a batch of concrete was ready it was dumped into the bucket of the bobcat and taken to the building site.  Thank you Tom, Stephanie, Robin, Jody, Mike and Linda for the loan of all of this equipment!

The bobcat is small and mobile enough that it could be taken inside the building walls.  The operator then lifted the bucket to the height of the forms and dumped the concrete out.  Unfortunately, the bobcat had just enough lift to get the bucket over the edge of the form and the bucket could not be tipped far enough so that the concrete would simply slide out.  We had to shovel the concrete from the bucket into the forms.  Still, this was much easier than building scaffolding and carting the concrete around in wheelbarrows!

After the concrete was dumped in the forms it needed to be shoveled (or vibrated) so that it flowed everywhere and eliminated any air pockets.  Finally, the concrete was leveled and smoothed so that it was consistent throughout the entire form.  We were not very concerned about smoothness as this concrete will not be exposed when the building is finished.

The last step was to insert the anchor bolts.  These bolts are spaced 4′ apart and will be used to attach a wooden sill to the top of the concrete bond beam.  The rafters of the roof will ultimately be attached to this sill plate.  You want to get the bolts in fairly soon after the concrete is poured and leveled, as otherwise it becomes unworkable.  We simply put the bolts in after we finished leveling another 10′ or so of the concrete in the form.

We started this job at around 9:30 in the morning and finished right around 5:00 in the evening with about a half hour for lunch.  We worked all day and our neighbors, Robin and Jody (thanks guys!), were there for about half of the day.  It was hard work but all of the equipment made the day go that much easier and painlessly (We still hurt at the end of the day!).

Some notes about the concrete …

The concrete for our beam is specified as 3000 PSI (pounds per square inch) with reinforcement.

The reinforcement consists of two horizontal runs of 10 mm rebar with vertical rebar every other tire driven into the top three tires and extending to within the top two inches of the form.  We also used engineering fibres in our concrete mix.

Our formula for the concrete was 1 part portland cement, 2 parts sand and 3 parts gravel.  The dry ingredients were added to the mixer with sufficient water to hydrate the mixed materials (you do not want to add too much water as this will weaken the concrete).  We then added engineering fibres and allowed the batch of concrete to mix for another couple of minutes.

I figured out that one 40kg bag of dry portland cement has a volume of about 28.6 litres.  We dumped one bag of cement (very heavy!) into the mixer for each batch of concrete.  This in turn meant that we needed 143 litres of aggregate (2 parts sand; 3 parts gravel) for each batch.  We filled 7 twenty litre pails and added their contents to the mix.  Generally, I slightly under filled the aggregate buckets to ensure that I was getting a slightly higher proportion of cement in each batch.  I did this to make slightly stronger concrete.

We ended up using 22-40 kg bags of portland cement which works out to slightly less than 4 cubic yards of concrete.  So, my initial estimate was pretty close!  I am glad that day is over.

We have already started prepping the roof beams, but I suspect we will start work on the front wall first.  The front wall is required to finish the roof, and I am not keen to have the roof beams installed and weathering in the sun while we work on the front wall.

Progress on the house

I have been busy this week investigating some possible work opportunities so Chris has been working a little on his own.  But this weekend saw us get a fair bit done on the house.  Most exciting, today (Sunday) we started plastering in our first pop cans (during the Canada/USA gold medal hockey game).  I drove the kids to Dad’s to watch it on TV and they gave us cell phone updates as the game progressed.  Yay Canada!

But I digress.  Here we go!

The bond beam form has been progressing…here is Chris bending re-bar for around the corners…

Here is what the inside of the forms looks like.  It is pretty standard…much like any foundation footing; however, this will support our roof.  We are using 2 runs of 10mm rebar.  We made our own hangers from used lumber strapping. 

As the forms were leveled gaps appeared between the wood and the tires (caused by the slight out of level of the top row of tires).  We checked the top row last weekend with the transit and there was no more than 2 inches difference from the highest to lowest tire!  Pretty good.  However, we need to fill in the gaps we have so that when we pour concrete, it doesn’t simply escape out of the bottom.  When pouring a traditional footing this is pretty easy; just mash dirt up into the gap.  However, when you are 8 feet in the air and the bottom of the “form” is a round tire, this becomes more problematic. 

We debated about whether we would scab on old wood while we poured, but in the end we’d have to take it off and plaster in between the tires anyway.  So we made the decision to plaster in the gaps on the top row right now, simply to be able to pour concrete (and hopefully not have to redo the work later).

The plaster mix is essentially a cob mixture made up of clay-soil (dirt), concrete-sand and fibre (usually chopped straw).  We found and borrowed, from the library, three plaster books we’d previously read.  The Earthship volumes are not heavy on detail about the plaster so we consulted mainly with The Natural Plaster Book: earth, lime and gypsum plasters for the natural home.  It is excellent.

One of the most important things to do before using native materials in a plaster is to determine the levels of clay in it.  Clay is essential in natural plasters as it works as a binding agent.

So we followed directions on how to determine the clay content.  We filled a quart jar 1/3 full of the dirt we hoped to use as the clay-dirt.  We then filled the jar to 2/3 full by adding water.  Then we shook it.  After 3 seconds the “gravel” settled out.

Chris marked this line and set the timer for 10 minutes.  In the next 10 minutes the finer sand and silt settles.  If the water is still quite cloudy, then you have clay in your soil.  Wait even longer and you can determine how much clay.

This was taken after about 20 minutes.  After the clay settled, we figured we had just under 25 percent.  This is quite high so when we mix our plaster we will keep this in mind (especially for the finish coats where we will be avoiding cracks).

Most plasters call for chopped straw for the fibre content.  The book we read mentioned sheep’s wool as a good alternative!  We still had two bags of wool left over from last year’s 4-H shearing day. I read up on how to wash wool to get out all the lanolin. 

Here are a few pictures of the wool during washing last night.

The house smelled a bit like the barn for a while!

Here we are pulling apart wool into strands so that it will evenly distribute through the plaster. Some of us are happier than others…

Today while the kids were watching the hockey game, Chris and I pulled a wheelbarrow each of clay-dirt and sand to the house next to the cement mixer.  We added equal shovelfuls of both.

After we added enough water to make the mixture “soupy”, we added about half a grocery bag of wool.  This was a bit of an experiment as the directions gave amounts for straw, but not for wool. 

After the wool is mixed in, the mixture was quite thick. Here’s the first handful thrown into the space between tires and underneath the bond beam form.

And after the first can is mashed in…hey!  it looks just like it does in the Garbage Warrior!!!!

Here’s a few in a row…

This is only the first step.  We need to let this layer dry, then wet the outside and do another layer with two more mashed pop cans.  We will do these two steps for the top round of tires so we can pour cement, but eventually all of the tires have to be done.  There are 762 tires in the building so far so that’s a lot of plastering.  Thankfully, it does go very quickly….