A lot of specialized experience and understanding are required to properly build an earth sheltered home.
Hindsight
Many contractors have experience, usually learned from mistakes made. Specifically, they learn from mistakes that negatively impact their portion of the build. They often don’t understand how the design or their adjustments and shortcuts will effect other portions of the build or the final performance. Many engineers have understanding of what effects the final performance, but don’t have the experience to understand how their instructions will be interpreted during real construction.
Contractors who do larger portions of the build are more likely to discover negative impacts of their earlier work and, therefore, build more experience. A General Contractor (GC) sticks around for the whole project and hopefully accumulates more experience (via hindsight) that he can apply to the next job. If you are GCing your own home, you need to figure out how to avoid mistakes rather than just learning from them.
Building Inspector
The building inspector is often a retired builder or someone with similar experience. They should be on the side of the home owner and help to keep the builders in line with acceptable practices.
However, for practical reasons, their inspections are only at certain key points in the process. The inspectors have a lot of other homes to inspect and can’t spend too much time at each one or keep up on understanding all the design intent. Even with a good building inspector, there is still a lot of room for serious errors that the inspections won’t catch. The GC and home owner still need to be vigilant.
For example… The building inspector checks out the footings before the concrete has been poured. He can see that the rebar and the forms look OK and may approve it, but he is unlikely to check all the rebar or all the forms. Even if they do check the prep carefully, they may not see what is under it and they are not around when the concrete is actually placed and the builders are stomping the rebar into the ground.
Anecdotes
Here are some anecdotal examples while I sort this out in my head… I am sure I will see more as I continue my build.
Rebar:
The engineer understands that concrete is strong in compression(20 – 40 MPa or 3000 – 6000 psi), but weak in tension (2 to 5 MPa or 300 to 700 psi). Reinforcement is used to increase the tensile strength and resist cracking. The Engineer understands that when the concrete footing is under building loads, its top portion is in compression (unlikely to fail or crack), but the bottom is in tension and needs reinforcement. at some point between these two, the compression and tension balance out to zero. Therefore, the engineer will often specify that the rebar should be placed in the bottom of the footing.
However, the engineer also understands that the reinforcing is pretty useless if it is not fully encased in concrete so that its tensile strength can be shared. So the engineer may specify something like placing the rebar 2 inches from the bottom of the footing.
Later, the guy installing the footing has none of this understanding. If you are lucky, he knows that he can use rebar chairs that will put the rebar right in the middle and he will probably do that if you let him. When laying out the rebar, they may not overlap corners like they should or worry about rebar being placed in certain critical directions where the tensile load is likely to be greater.
In other situations, the installer may have no concerns at all about pulling the rebar or welded wire reinforcement (W.W.R) up into the concrete to place it at the correct depth. They will just stomp it down and focus much more on the surface finish (that you see when you pay them) and not spend any time worrying about what you can’t see.
Getting this wrong is not something that they notice during the install (no failure as far as they can see), so you can’t trust them to get it right by experience. The guys on my project made all of these mistakes and probably more. I talked to them about these things as they came up and realized that while they have many years of experience installing footings, they had no real understanding of why they were putting in rebar or why it mattered where it went. As a GC on your own home, you will need to keep a careful eye on your installers and inject some understanding (or just tell they what to do) as needed.
Forming
Here is a case where experience is the most important thing, probably because failure happens during the install. An engineer can calculate lateral loads in mega pascals, he can understand how those loads translate into forces that will try to tear the form-work apart. Meanwhile, the experienced builder has felt the weight of the forms in his hands and the compactness of the dirt under his feet. He has seen these things fail and really wants to prevent that from ever happening again.
In my case, one of them said “put as many stakes in as you think you need to keep the forms in place, and then add two more.”
I still had some bow outs on my build because they overestimated how well the sand could hold in stakes, but generally speaking, their experience was an asset.
For my garage, the plans were a little unclear on the depth of a grove that was to be formed in the top of the concrete to catch the base of the wall. I understood what it was for, but thought it was based on the depth of a 2×10 board (1.5″ x 9.5″). The first guy to work on it had never done anything like this and did the work on a day when I wasn’t around, so he put the wrong sized board in the wrong place, etc. I contacted the boss the next day and he send out someone else to fix it. The new guy stiffened the board and placed it 3.5″ into the form. While he was working, I noticed it was “too deep” and went to ask him about it. He just looked at me and politely said, “I have done about 20 garage slabs for quonset huts and they always do it like this.” Recognizing experience (and confidence), I backed down and went to check the plans. He was right (and I let him know).
Since the shotcrete went up, I have been working on other things such as getting my drain tile in and getting the basement plumbing done. That is covered in the previous post (posted later in time, but shown lower down in the list of posts because of its date).
This is how things looked after the shotcrete was finished (and we got down the drain tile)
Progress is being hampered by the fact that the shotcrete left a lot more concrete on the floor than expected. Instead of being a thin crust that breaks easily, it is 2 to 6 inches thick and pretty solid across the whole floor. This was mostly due to shotcrete blowing thru the lath and on to the floor inside. The mechanical room has it the worst because it is a small room with shotcrete coming in from all sides. I will need to rent or hire a jack hammer to sort it out properly.
This shot is after spending an hour with a power chisel.
I dug out several other areas for drains and to allow the radon pipe to exit…
But I still need to run the drains and radon pipes thru the rest of the structure, and I would guess that this lumpy surface will make it much harder to get the underfloor insulation and radiant floor tubes in place. I am even a bit concerned about broken pieces of concrete tearing the vapor barrier.
I have a crew lined up to get in there to chip the rest of it out, but they are not available for another week or two. And of course, this was not in the budget.
Today was day 3 of the footings… Our first day pouring concrete on the site. The actual work was really all done in about 2 hours, half an hour if you just count the concrete pour time, so it is hard to call it a day. The inspector, Dale, needs to check the footings before the pour and his MWF 10 to noon schedule meant we couldn’t fit this into Monday afternoon like the footings guys wanted.
Here is today’s timelapse video;
Thunderstorms were predicted for 1:00, so I called the building inspector to see if he could put me early on his rounds. He agreed and put me first. I texted Doug Dysert by 8:30 and hoped that would be enough lead time to move the pour earlier…
The inspector arrived just after 10 AM. Keep in mind, this was my first inspection, so I was a little bit nervous. The first thing he did was check out my posted permits. Then he went down into the excavation and gave the forms a good look. The inspector was actually very friendly and said the design was a “work of art” and the execution was “very well done”. He found a couple spots where the rebar was a bit too close to the boards (there is supposed to be at least 2” between the rebar and the forms) and told me to sort that out before the pour. We chatted a bit and then he handed me my “Inspection Notice”, with “approved” written on it. He left by 10:15.
I texted Doug to say we were all ready for concrete, but it turned out that the concrete was scheduled to come at noon anyway. Two of Doug’s guys (Don and Chris from the previous day) arrived at about 11:45. The concrete mixers (two of them) and the pump truck all arrived around noon. It was pretty awesome to see the pump truck extend its huge feet and then unfold its 135 ft arm. I wish the timelapse camera had been angled to catch it.
The concrete pump truck was pretty huge. Its 400 horsepower Cummins diesel motor powers 4 powerful pumps that push the concrete at 4800 psi. The operator told me that he could pump up to 210 yards per hour, but he had it set on the slowest possible setting for my small job. I got my order slip from the driver to confirm that it was 2500 PSI concrete with a slump of 5 inches. It had the ¾ inch natural stone aggregate (6A) along with sand and fly ash.
Fly ash is what Charles Dickens would have seen coming out of the smoke stacks of dirty coal factories before they started capturing it. Trapping that pollutant it in concrete is a good thing. It is also pretty much free (waste product) and replaces some of the Portland cement, which has high embodied energy (and cost). Its tiny particle size increases workability (think tiny ball bearings) of the concrete, so the water content can be reduced, which increases strength and durability… It is really a win-win additive.
Then the clouds parted and the sun came out. The concrete got pumping and things went pretty fast after that. They pumped out most of the 23 cubic yards of concrete in about half an hour. I don’t think the crew had enough people to keep up like they would have preferred. I jumped in to help with the screeding. Even the pump truck operator helped moved the concrete pipe around when he got tired of waiting. The concrete was pretty thick with ¾ inch stones. None of the footings blew out, but it did bulge in a couple spots, which used up more concrete than we were expecting…
For footings, they just screed, they don’t trowel or float. Since the tops of the forms were already level, screeding was just a simple process of “sawing” a board back and forth over the top of the form to level it out.
We ended up needing to use the concrete that was in the bottom half of the long pipe to fill in the last bit of the forms. The pump driver basically dumped it on the sand at the top end of the driveway and we had to bucket it over and down to the footing. Don was using a 5 gallon bucket and I was using a 2 gallon bucket (only other bucket available), but I joked that at least I was filling mine up all the way.
With the last bit of concrete, I built myself a 5 gallon bucket rocket stove. I made the inner form out of cardboard (the night before) and wrapped rope and saran wrap around it to “spiral” the flow. My hope is that it will make a little flame tornado that will push even more heat into the concrete and increase the draft further. I’ll make a separate post on that if it works. This concrete wasn’t exactly designed for high heat so it may not last long.
Then the rain came down again. It was actually a line of storms, hundreds of miles long, all lined up to pass over my site, and nowhere else. They guys thought it would blow over soon and decided to wait it out in the truck. I got in with them and asked how long we would be able to push the vertical rebar dowels into the concrete. They told me not to worry about it, we had “hours”…
Well, nearly an hour later, and the township tax assessor called and asked me to drop off a copy of the plans. The assessor had been out to view the site while we were not there and was totally confused by my footing. She was only about 2 miles away, and I wasn’t doing anything right then, so I took the plans over to her. I hope she devalues the home as much as my bank’s appraiser does. Unfortunately, she seems to like it.
When I got back, Doug was on the phone. Understandably, He didn’t want his guys to sit there waiting any more. He said they could just drill the rebar in later (for ~60$/hr). As I hung up with him, the rain stopped. We went down to check out the concrete and found it was already too stiff to hammer the rebar into anyway. It wasn’t my plan, but now I will have more time to carefully mark the position of the dowels, so it may be for the best.
Not sure if it was just the dollars talking, but Doug really didn’t like idea of the PVC tubes as rebar receptacles. He pointed out that they would be a weak point in the connection between the footings and the rebar. They do not have the strength or the grip. I was more interested in the convenience because I don’t think I need strength or grip in that location. Perhaps we were thinking about different locations. I agree drilled rebar will be critical for the pillars under the concrete ribs. Not sure if we will use the PVC when we get to the main footings, but I have 250 of these things cut and ready to go.
The rain washed off the concrete “crème” and left an exposed aggregate look. I kind of like it and I think the shotcrete will stick to it well. Another “day” done.
I still haven’t seen the bill (or paid anything). In order to get a reasonable bid on this unusually complicated project, I had to get the bid based on “volume and materials”. I thought that was safer than “time and materials” because at least the volumes were calculated beforehand. Basically, I agreed on the cost per cubic yard for forming and pouring as well as the cost, per ton of rebar, for placing and tying the rebar. But I do not yet know what he will charge for the materials (such as the wood, rebar, and concrete) or the total cost of the pump truck, or how the over-orders of material will affect the bill. I am a tiny bit nervous about that.
