Our earth sheltered home relies on thin shell concrete to support the earth loads. I do know of large earth sheltered homes with >50 ft domes made of thin reinforced concrete less than an inch thick, but that sort of precision is difficult. My vaults are relatively small (<15 ft across), but will be 6 to 8 inches thick of very strong (>8000 psi) shotcrete. Once that shotcrete has set, it will be very strong, but before it sets, it is very heavy and needs to be supported.
Rather than build a separate frame to support the structure which will later need to be removed, I am embedding a rebar skeleton within the structure that will support it while it cures and then reinforce it for the next few hundred years until its final job is making it very difficult for someone to tear down.
The #4 rebar is spaced 12 inches apart (horizontal and vertical), tied and then welded (mainly because my family is climbing all over it). We then use metal lath on the inside, tied to the rebar, to catch the externally applied shotcrete.
You can see how the shotcrete was done on the basement level in this old post. Due to the mess of shotcrete passing thru the metal lath in our basement, we have decided to add an additional layer of fine fiberglass screening to the bedroom. The fiberglass still needs to be backed by the stronger metal lath, but it should prevent much more (probably all) of the shotcrete from passing thru.
I don’t want to go back and look at my gantt chart (schedule) to remember how long this process of rebar and lath for the bedroom wing was supposed to take. Actually, I don’t even think it is taking much longer than I estimated. The real problem is that I work full time (and even spent 2 weeks traveling to Germany for work) and there were other important things to work on (the electrical service entrance, ribs and quad deck floors all took more of my time then expected, those videos will be compiled sooner or later), so I just didn’t get to put enough time into this frame.
Of course, I wanted to push thru and try to get shotcrete up before winter, but then I got thinking about all the other things I had to do first, such as install the electrical conduit and build forms for the skylight curbs, and I decided I had best take my time and do it right.
Strategically, I also decided that if I focused on the electrical and garage instead, it would give me an enclosed workshop space to work on those skylight curbs and other forms over the winter and I would be in a better position to proceed in the spring. Hopefully, that works out as planned.
The Side Stories
Zack (the teen I met thru the high-school guidance councilor) has been helping me off-and-on for a few months now. Zack has many siblings, mostly little girls, but a couple times he has mentioned that he has an older brother named “Will” that would like to help. Now that we are tying rebar, there is as much work as they can handle, so I told him he could bring his brother. It turned out that Will couldn’t make it, but Zack said he would bring another brother. He didn’t give the name, so I told my wife, Sherri, that I would guess it. I figured they were going for late letters in the Alphabet because they already had a “Will” and a “Zack”, so I predicted that they would use a “Y” or “X” for the next brother. I couldn’t think of very many names that began with those letters, and figured that Yuri was unlikely (in our Dutch/German area), but since they went with Zack, I bet my wife that his brothers name would be Xavier… I was right.
Sorry if that rotating scene made anyone sick. At first, I thought those rotating scenes were pretty cool, but I may have run the speed up a bit too high in the final edit. I can’t promise not to do it again because I ended up using that mount a few more times to film scenes for upcoming videos ;^). The mount was basically just an Ikea cooking timer that I added a 1/4-20 nut to the bottom (to fit my camera tripod) and a spare go-pro mount to the top. It makes one full turn per hour. This is the Youtube video that I followed (roughly) to make it. It cost less than $7.
There is one sequence in the video where Michael (my 9 year old) is climbing all over the outside of the master bedroom vault. Moments later, Sherri is doing the same thing to tighten all the wires (note her clearly “Egyptian” stance). Anyway, I thought this would freak out my mother-in-law pretty well, and I kind’a like doing that from time to time, so I rushed that clip thru a mini production and put it up on the Facebook site (which you can join up on the right side of this page). To my disappointment, it didn’t surprise her at all. She either didn’t think it was very high or dangerous or she is getting quite used to Sherri doing all sorts of crazy things to build this house. Oh well.
My generator was on the fritz a bit in the middle of all this and there were several weekends where it would only start on the rare occasion. It started often enough that I didn’t want to spend hundreds of dollars to replace it, but rarely enough that it really killed efforts to get this rebar up and kept shifting me to other jobs that didn’t require electricity. Eventually, we decided that enough was enough and got a new generator. Of course, we got a bigger one. Suddenly my welder has a lot more power and I can weld that rebar much more quickly, so woo hoo. Anyone want to buy a used generator with a mystery starting problem?
Just some pics and timelapse stills from this portion of the build.