And your not going to see any of it!!!

Was the mantra that was repeated over and over by my labouring wife over several months of preparing the house site for the pouring of the slab. This is the last expensive thing we need to do before getting on with the relatively cheap mudbrick making. I really can't blame her it has been a bit of a slog but we can now see the end of this stage of the house build.

To ready the site for pouring the concrete slab it is simply a matter of digging the trenches, adding a layer of sand (road base?), boxing up, covering it in plastic and setting out the steel reinforcing. We have done these steps but of course we added an extra level of difficulty.

Firstly we put up the frame and roof before the slab, which is not normally the way it is done. The main reason we did it this way was to get the house build started quickly so that we would be able to extend our planning permit (ie. frame stage finished). It has had an advantage in that we don't have to worry so much about the weather when preparing for and when we eventually pour the concrete. But we have had to dig the trenches by hand (or pick, shovel and wheelbarrow), which added up to moving about 16m³ of dirt. This was done over a period of a month on the weekends. Because the outer edge is curved half the trenches ended up being curved. The total length of trench was about 160lm. The dirt we moved was dumped next to the house and will be used for the mudbricks and render later on.

The next step was covering the bits of land with about 8m³ of sand. This was done by wheelbarrow and shovel. We compressed the sand by hitting it with a bit of 4x2. The sand needs to be slightly wet to do this well, too dry and it won't hold it's shape, but too wet and it is too sticky.

The boxing up was also a bit different and I think a bit easier (and cheaper) than if we had a square slab. The entire outer edge of the slab is curved, so I decided to use 3ply because it is easy to bend instead of 6x2's that you would normally use. I used scraps of 4x2 and 3x2's upto about 500mm long to stake the 3ply. The bits of wood were staked to the ground with 250mm galvanized fencing nails (these will be re-used for fencing once the slab is done) and then the 3ply nailed to it. The slab is 150mm above the ground level so the 3ply was cut into 200mm strips. Because the 3ply is curved this adds strength to it and hopefully it will hold up on the day of the pour.

Laying the plastic we thought would be a bit of a nightmare seeing as how half the trenches are curved and at odd angles to each other and the added difficulty of working around posts. But it wasn't all that difficult and only took a day. We used about 400m² of plastic to cover an area of 200m², I guess it was in the up's and down's of the trench walls, the overlap of the plastic and a little extra in the trenches so when the concrete is poured it doesn't pull the edges in too much.

The last bit of the preparation really highlights one of the reasons most people don't make a round house. Trench mesh is straight and is really, really hard to curve. So we had about 80lm of straight trench which was easy to lay standard 3xL11TM in. The outer edge and inner trench which made up 80lm of curved trench needed to have 3xN12 bar, which is 12mm notched steel bar, which needed to be curved. This ended up being not too hard to do, but did add a lot of extra time over installing standard trench mesh. There also ended up being a lot of extra cutting of the slab mesh (SL82) because it has to follow the edge of the slab. We also had to navigate the 10 central posts and cut more than half the 18 6000mm x 2400mm sheets used to fit around the posts. But myself and the wife got the job done in about 4days with a bit of help from the kids.

So now we are ready bury the whole lot in about 40m³ of concrete, we just need to organise the concrete, concrete pump and helpers for the day.

Mud and wheelbarrows - the footings

We were incredibly fortunate to have a small group of helpers (both family and friends) to assist us with our first concrete pour last weekend.  We were incredibly unfortunate to have ALOT of rain the night before the pour, so after concerns about it being too hot to pour, we had concerns it would be too wet!!!

Our stirrups - these things are built to last!

We spent most of a week preparing the site, and having our site inspection (which we passed!).  To make sure that all our stirrups would be lined up perfectly and would be easy to get right and check once the concrete was poured, we spent many nights discussing and brainstorming how to make it work on the day.  We decided on bolting 2 pieces of timber to each stirrup shank, tight enough so that it would not move.  This timber would sit on the ground, and the height could be adjusted by loosening off the nuts, and pulling the stirrup up or down.  This meant that the height would be right.  To make sure the exact location within the hole was right we set up a string line with marks on it, and once they were all 'perfect' we sprayed the ground and the wood with marking paint, so that the position was clear, even if the stirrups were removed from the hole.

How we braced the stirrups and lined them up ready for the concrete.

As it turned out, we had enough people so that some were to push barrows full of concrete, while 2 would stand of the timber supports to hold the stirrup in place as the concrete was poured in.  The 'holding person' also was able to help with tipping the barrow.  Although the stirrups and the supports got a bit in the way, the whole thing barely moved, so it was just a matter of going through and double checking them all after the concrete was poured, and reduced the stress levels considerably, as we didn't have to stuff around putting stirrups into concrete and lining them all up afterwards.

Pushing wheelbarrows full of concrete through the mud, not an easy task.

We had 20 holes all up (so therefore 20 stirrups), in two circles, which we call the inner circle and the outer circle.  At each of these we will fix our posts and then the beams will radiate around to a central collar.

double checking the distances after the concrete was poured.

Our concrete pour was a fun day.  It was muddy and difficult (the mud clogged up the wheels of the barrows, so they were really hard to push or control), but there is a sense of comradery when doing a task like that with a group of people, especially when everyone can work well together as a team.  We are indebted to all that helped us that day.  It was all over within an hour or so, but it was fast paced and challenging at the time. 

How the wheel of a wheelbarrow looks after numerous trips through the mud.

Next step - the frame!


A huge thank you to Paul, Grant, Pete, Karhen, Claude and Margit for your help!