Introduction: Building a Dome Out of Paper (and Steel...and Cement...)
Since we would have a lot of batteries and solar PV equipment that needed a good home we decided to do our first structure as a battery room for our solar equipment. Domes are inherently strong and energy efficient structures. This is how we started building a battery dome from paper.
Step 1: The Plans
We used sketchup to create 3D models of the underlying structure. Rebar, 6x6x10 remesh, and expanded metal lath were the bones holding this thing together. We hired a structural engineer to review our plans. Once we received his stamp this made it easier to approach our local building inspector. This is a small dome only 10' in diameter. However, it is really really strong and insulated to somewhere between R30 - R40 range. Ideal for keeping batteries near room temperature with no additional heating/cooling required.
Step 2: Rebar Work
We had a existing concrete slab so we just used metal plates anchor bolted to the slab and welded our rebar arches onto them. It was a little shaky getting the first few arches in the air, but the small dome is so manageable that it really was not a big deal. After the arches went up we started doing hoops around them. Everything is welded (a no no for rebar), but with a friendly engineer that can be dealt with. The welded rebar allows us to climb on the structure early in the building process. This makes it easier to tie remesh and lath to the dome.
Step 3: Lath
It is traditional in ferrocement work to tie lath by hand. This gets old, real old! We used a pneumatic tool to tie our lath to remesh. Can you guess the difference in time savings by having this one tool? It was about 3x. We normally would lath 4 sheets a day by hand per person. Once we had the pneumatic gun we were doing 14 sheets a day. Still slow work, but easy and fun compared to lifting 40lb compressed earth blocks.
Step 4: Fill 'er Up
We knew that it was possible to move our papercrete mix with a pump. This dome used a simple recipe of 2 parts paper to 1 part portland. Our current larger domes are using a lime/clay/paper mix. Anyway it took a while for our pump to arrive so we prefilled the dome with some old papercrete blocks and I bucketed for a few weeks. The bucketing sucked! Eventually our 9HP 3" trash pump arrived and it worked great. It uses a lot of water, but it can move paper through a 50' hose and up a 10' vertical climb.
Step 5: Plastering
Our papercrete based plaster still leaves a lot to be desired. We ended up using a mix of prickly pear cactus juice, old house paint, 1 part paper, 1 part cement. Later there was plenty of cracking on the areas that received a great deal of sun. We have had better success in other types of paper plasters. We used a tirolessa sprayer which made easy work of plastering the inside and outside of the dome. This is another amazing time saving device and it works well with pretty much any type of finish from earthen lime plasters to heavy cement/sand mortars.
Step 6: Equipment Setup
After letting the dome dry for weeks after pumping in the paper and more time after plastering we brought in our solar gear. We just welded angle iron to concrete anchor bolted plates and against the rebar of the dome. We also had to hack up some pallets for the batteries.
We tried all sorts of home made paints. In the end we used a white roofing sealer and tinted into brown using brown umber oxide. The home made prickly pear paints and lime washes were simply not robust enough to handle moisture. Again this is due to our limited knowledge in plasters and finishes.
At the time of this submission the dome has been finished and running all of our PV solar equipment for nearly a year. We are quite happy with the thermal performance of the dome as well as the asthetic look. It cost about $10 a square foot for raw materials to put it together. We have since started a 20' diameter dome (~320 sq. ft). It has been quite simple to assemble although extremely time intensive. We plan to make three more domes. Feel free to make some suggestions as to how we can improve, speed up, reduce costs, etc.
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