Last year we helped out a number of times at another local Earthship owned by our friends Dash and YP.
Here is a picture of the front.
Now this Earthship is made using domes. It’s modeled more off the simple survival model, rather than the global model. The roof for this is quite a bit different.
We filled in between the domes with dirt, then we covered that with a vapour barrier. The next layer was 10″ (25cm) of rigid insulation which was then covered by a waterproof membrane made of EPDM rubber. The last layer is a concrete slab to cover it all. The slab is used to provide a nice surface on which you can catch water to fill your cisterns.
Well, last Thursday (Oct 11), Dash & YP got a crew together and we poured the slab on top of the roof. Everything was prepared, the forms were made and the metal reinforcement put in place. Here are some pictures of that.
Now when they said they were getting a concrete pump truck, I was imagining the kind with the huge boom attached to it that would hang over what you were pouring, so I was surprised when this showed up.
It’s a similar idea to the boom truck, but small scale and no big crane. You dump the concreted into the hopper at the back of the pump and it pushes it through the attached hose to where you need it to go. A little lower tech, but entirely sufficient for what was needed. Probably cost less too.
Here you can see the hose reaching to the far corner where we started. The truck had seemingly a mile of hose and we only used about four lengths of it so I would imagine that the pump can push the concrete through quite the distance of hose, if you need it to.
Once we got started, it seemed to me a lot like frosting a cake. You squirt out a bunch of concrete frosting and then spread it around into a nice arrangement.
The rate of flow through the pipe is pretty quick so you need to be on the ball as each section fills up quickly.
It didn’t take us very long to fill the whole thing. As we got closer to the end, we would remove sections of the pipe to make things easier. It’s really heavy duty hose, I’d guess around 6″ (15cm) in diameter and you don’t want it piling up or getting kinked.
Voila, finished roof slab.
I do have to mention that the concrete guys were very dubious about this. Questions like, “you want to do what?” and “do you realize you’ll be adding around 40,000 lbs (18,000kg) of weight to the roof?” came up.
I should also mention that of all of the concrete that was used to build this structure, this roof slab is probably one of the few exceptions where using hemp-crete is acceptable. I talked about hemp-crete and the dangers of using it in my Thermal/Solar Heating and Cooling post. In this case, however, the roof slab is not adding any thermal mass to the structure. In fact it is insulated away from the main mass of the building, so using hemp-crete, if you so desired, would only add more insulation. What I don’t know is how porous it is, so you would probably need to add a sealer to it the same way you do regular concrete.
In addition to the roof, there were some interior footings that we poured as well.
Dash and YP hadn’t originally planned to build the interior glass wall that separates the living areas from the green house. They still might not, but they decided to pour footings for those walls in case they change their mind.
We had some left over concrete at the end and we used it to do pack-out between the tires in the interior. That’s where you fill in the cavities between the tires to build the wall out so it is smooth.
All in all, a very successful day.