This was the hardest part of the entire Conduit Dome Wire and Cement project so far – it was my first attempt at working with cement (other than using a couple bags of ready mix to set fence poles). To make matters worse, We were being filmed by a crew from Doomsday Preppers so we were on an extreme time limit (basically we had one day to do all the cement work), I only had one helper (Thanks Dad), and my mixer kept breaking.
All in all, I am pleased with the outcome, and learned a lot about what to do, what not to do, and how I would do it if I ever do it again….
What we did up to this point was to build out dome and frame in the door. Now we have to prepare for the cement.
Our intent is to cover the dome using a concept called ferro-cement (FC). In ferro-cement you don’t have to use as much cement to cover a structure because you are using more structural wire – the ideal is chicken wire every ¼ inch or stucco mesh.
In most instances of using FC workers use a thick mix of Portland cement and sand 1/3 ratio, and work against each other to press a low slump (little water) mix against the wire.
This is very labor intensive, and since I just did not have time, I contacted Nolan Scheid from Mortar Sprayer.com and got his air powered sprayer.
I will say, that in my ignorance I did most everything wrong at LEAST once, but his Sprayer enabled me to complete the job on time (well, that and my Dad’s labor)
I don’t want this article to sound like an advertisement for his sprayer, but I cannot express how vital it was to this process.
That being said, since my budget was too small to afford stucco mesh or enough chicken wire to wrap it 4 times to get the ¼ inch between wires, and I did not know about spider lath at the time of my project, I was worried about the sprayed cement blowing through the wire. (I learned later that it depends a lot on your technique). So I allayed my father and my fears somewhat by adding some surplus billboard tarps I bought online, these tarps are old vinyl billboards and are extremely thick and durable. I originally got these for a pond project, but I was too lazy to hand dig it. I think I got them for under $30.
My original plan was to wrap the dome in welded wire fencing, then the tarp, then the chicken wire, but on site, we began over thinking and changed to covering the frame with the tarp, then fencing, then the 1 inch poultry netting. The thought was that this would allow the cement to get the benefit of the extra iron in the fencing. This caused problems when we started spraying (more about that later.)
The way we used the fence wire was to divide the ground perimeter of the dome (54 feet) in half and cut the welded fencing wire into 27 foot (plus a little extra) sections. We allowed the wire to roll back up into a loose roll. Next we bent one end back about 6 inches, pressed it under the base of the dome, and the used long poles to push the roll up and over the highest point of the dome.
We did this several times, each time pushing several inches of each end under the base of the dome to give us attachment points when we pour the slab.
We also pulled the fence wire as tight as we could to keep it tight against the dome frame.
We cut left over fencing wire into 5 or 6 ft. lengths and attached that wherever the long rolls did not overlap. We used rebar wire tires to tightly attach it.
We also took a section about 15 ft. long and rolled it over the door frame section to make and “igloo” type door.
It was hard to keep everything tight and round, my Dad did a wonderful job of pressing down on the raised sections using a 2x2ft section of plywood and tied everything down smooth while perched on a walk-board. (I blame my dislike of heights on watching too much MacGyver in middle school)…
Next we wrapped one 55 ft. length of fence wire around the base, and the forced it to fit the frame. The wire will want to stand straight up, but the dome slopes inward.
It took a lot of fighting and much wire to get the wire nice and flat.(we used a whole 1000 tie bundle of rebar wire ties on this small dome.)
You cannot tell the work put into making the dome smooth with the finished project because of the burlap roles that are supposed to “camouflage” the building, but when we do the inside, the work will show in a much smoother surface.
Before we added the chicken wire (which I found that professionals call poultry or avian netting), we installed the two skylights. (the picture shows a bottle that is not full enough – in actuality the bottle works best completely full – but probably not in the winter if you have hard freezes).
The bottles don’t look all that nice, and I got a lot of questioning glances from both the film crew and my Dad (he is a perfectionist when it comes to building), but when the cement dried, and we took off the plastic bags we put on it while spraying cement, they were all amazed at how well it worked.
We also used this time to install some plastic conduit so that we can later run electricity to the building. The way we created the igloo style door, I plan on eventually adding a solar panel to the roofline, but My dad wants to put it on a moveable stand so it can track the sun. He is probably right, but I think my way will look cooler – In the end, we will probably make a stand.
The last adventure in building gizmos was to create a “rain catchment system”.
The Doomsday Prepper guys were the big push for this – I was not really sold on the idea, but I like to please.
In doing my ferrocement research I found a cool website where a guy added planters to his dome (this is an awesome idea and is worth a look) – I figure that if my rain catchment system fails (and since it is not level it WILL fail) – I will use it to plant blackberries or Muscadine grapes to cover up the dome – even though I will have to be careful about it creating cracks in the dome.
Next we wrapped the entire dome in Chicken wire, doubling it up so as to get as close as we could to a wire every ¼ inch.
It took us two full days to get to this part – it should not have taken this long, but we had to work with the film crew – and re-shoot several key parts over and over to give the editors things to work with. (I am not complaining – just giving an overview of why a 1 day job took 2) – we did get to mix ONE load of cement that first day. I must admit, that that was the first time I had ever mixed cement, and was unfamiliar with how to use a cement mixer – the result would have been comical, if I was not worried about not getting the dome done in the time allotted (note – I was not worried about finishing the dome – I knew that would happen – I just did not want the film crew to leave and have it edited to look like a failure).
Luckily for my stress level, the next day the film crew had to film someone else, leaving my Dad and I one whole day to work the cement.
Unfortunately we had to hash out the stress of the previous day before starting to work, and my mixer broke after just a couple of batches. (While the instructions on the Harbor freight mixer do not mention it – put Loctite and a lock washer on the driveshaft that runs the actual mixer barrel– both sides)
Being out in the COUNTRY – going to the nearest hardware store took an hour and a half – during which time, my Dad hand mixed the cement to the specifications mentioned on Nolan’s Mortar Sprayer website – his cement worked MUCH better than mine.
We were able to spray the concrete using the sprayer, and it saved our bacon, but as I mentioned earlier my change in the structure caused problems when we began to spray. What happened was that any cement that blew through the wire (I started with too the PSI set too high, and did not have the sprayer close enough to the wire). The cement then collected on the tarp causing it to bulge out away from the wire. I should have gone with the original plan.
If found that by getting closer to the wire, more stuck to it, but since I was running out of time, and because the camera crew wanted the dome to be camouflaged to look like a boulder (Hey look, a boulder – I wonder how it got the skylights, solar panels, and big metal door…) I wrapped burlap into the chicken wire which helped catch the sprayed mortar – it also allowed me to sculpt the dome so that it had “wrinkles” and boulder like features. This did have an effect on the strength of the dome, but after the dome cures, I will tear out the tarp and spray and plaster the inside of the dome with more cement so that I get more cement into the wire. Hopefully this will make up for the strength I lost.
Luckily we were able to get everything done in time, because while I thought I would have Friday morning to do any last minute tough ups, the film crew hired a painter to paint the dome like a boulder.
He did a great job, and used all sorts of nice grey shades, so instead of a nice cement grey “boulder” we have a nice painted grey “boulder”
I don’t want to sound snarky though, because I really am happy with the project, and once I get a round “tuit” and finish the dome, I think it will make a great small classroom for when my range gets built, as it is very close to where we will set up our pistol range.
Until that happens, it gives me a lockable space to keep tools and camping materials for when we spend time on the property getting it ready.