Welcome to 2015… Hopefully, the year we get most of this earth sheltered home build done.
At the moment, things are pretty cold for building with concrete. There are ways to cure concrete in freezing cold weather, but the additives often reduce strength and/or corrode the reinforcement, so I am mostly working on planning. I have also pretty busy at work and got going again on my MBA, I am doing a business law class this semester. I go out any time the weather gets above freezing, but there were a couple weeks over New Year’s when I didn’t make it out to the site at all.
I guess my neighbors got a bit concerned about my seemingly lackadaisical approach to construction, so the neighborhood association wrote me a letter reminding me that I only have a year to get it done. They also reminded me that I have some legal liability if anyone (particularly children) get hurt on the site and asked me to fence it off. I wrote back that my mortgage company also wanted me done within a year, but has much bigger financial teeth than the association, so they don’t need to chase me about it. I also agreed that the construction fence was a good idea, at least from a legal perspective.
I went out to the site and just strapped some of that cheap orange construction fencing directly to the steel studs around the basement. More importantly, we took down the tempting scaffold tower so that we would be a less “attractive” nuisance to our neighbor’s children. I also put up a bunch of “Warning, Construction Site” signs. They are more for legal purposes than anything else.
Around about this time, I also started to bury my footings. I am sure that seems strange, so I put some fancy power point graphics into the video for a little extra explanation. The short story is that we need to fill in a couple hundred yards of dirt around the footings before we build the walls so we can use the skid steer instead of hand tools…
I had planned to bury the entire main level footing, and then hand excavate the top of the footing again so I could start bolting the steel to it ahead of the spring. But the ground is just too frozen to work with properly, so I am putting off that task until spring and have switched to focusing on tasks that can move forward, such as mounting the hardware for the basement stairs and central tower structure.
The video on those other tasks will come later, but here is the back fill video:
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).
These things usually start early in the morning… This morning, we were all ready to get these footings poured without any of the usual last minute running around. Three concrete mixing trucks were waiting at the bottom of the drive way as a dozen guys from Dysert Concrete arrived. The concrete pump truck arrived and while it setup, the guys were walking around and scratching their heads about my strange layout. Some were even taking pictures with their cell phones.
I showed some of the guys where the garage formwork had been done incorrectly and they started figuring out what to do. I was nervous because the first few guys clearly had no idea how to mount the groove form… But then a guy showed up who clearly knew what he was doing and took over organizing that work while some of the other guys got to filling the other forms with concrete.
The concrete mixer trucks dump their concrete into the back of the pump truck. The pump truck comes equipped with powerful pumps that can push the heavy concrete thru its 135 ft boom. The operator has a remote control box and walks around with a few of the of the concrete guys to control the movement of the boom and the flow rate of the concrete while they guide the end of the pipe along the form. It is quite something to hear that concrete falling down thru the pipe. For a big job like this, the pump truck really is worth the money. The alternative would have been trying to position the mix trucks around the site and push or wheelbarrow the concrete to the inner parts of the forms…
Initially, they overfilled the forms. The thin lap siding formwork was not strong enough and started to give way and lean out. I guess there were not enough stakes in the soft sand to hold back that much pressure. And after that, they filled the forms only half way and gave it some time to stiffen up a bit before coming back for a second pass. After the forms are filled up, they simply screed them off. It was amazing how the weight of the concrete pushed out even the 2×12 boards.
Meanwhile, the larger group were still working to properly finish the groove forms for the garage.
By the time the form for the garage was ready, they had already finished pouring the footings for the rest of the house. They started by filling the perimeter of the garage footing. They gave that a little bit of time to stiffen up because this was 18 inches thick and even more likely to blow out. While they waited, they pushed in vertical pieces of rebar along the middle of the floor to mark the floor slope.
Eventually, they started filling up the slab area, but quickly ran out of concrete. Another whole truck arrived and they dumped it out, but it didn’t go too far either. Along the way, they were screeding off the surface with long poles and leveling the concrete against the side of the forms and the rebar pegs in the middle. On the right side of the below picture, you can see the power screed that they used.
I noticed a slight bulge were my radiant floor pex tubes went under the concrete. I pointed it out and they said that it must be floating up. They said I should have tied it down every 8 inches… I thought that they (as experienced professionals) should probably have checked that before starting. Anyway, since we were waiting for the next concrete delivery to come anyway, they just gave the concrete a little time to stiffen and then pushed the pipe under (using long sticks) and pulled concrete (screeded) over it. I was still very nervous that it was still too close to the surface, but they told me it would be fine. I didn’t think until later that I could have put a piece of that 6×6 inch welded Wire reinforcement over the pex pipe to make sure that it stayed down…
Another truck load of concrete arrived and was pumped out. This time my concern was that the 6×6 WWR (Welded Wire Reinforcement) had been stamped down too much, especially at the front of the garage. Like the rebar, this welded wire reinforcement needs to be fully encased within the concrete to do its job. It doesn’t do much if it is trampled down under the concrete. I had been pestering the guys to try to pull up WWR elsewhere, and they made some halfhearted attempts upon each request, but at the front of the garage, where the slab sloped to the full 18 inches thick, it was so trampled down that I concluded it would be hopeless to ask them to pull it up… Instead, I waited until they got the got concrete in, and then I brought over two more big pieces of WWR and laid them on top before they guys had a chance to screed things over… Hopefully, these additional pieces stayed within a few inches of the surface where they could do their jobs.
With only one little corner left to go, they sent the pump truck home and we waited for the last concrete mixer truck. Most of the crew left also, except for two guys who were going to hang around and do the finish work on the slab.
After the last couple yards of concrete were in place, the senior guy used a power trowel to work the surface. The younger guy got busy working on removing the wood that held the groove form in place. Since things were now setting up quickly, my family and I rushed to press our hands into the stiffening concrete.
They took the power trowel over the surface 4 separate times and did a pretty good job there and on visible edges of the slab.
All in all, the footings and garage floor took 78 yards of concrete. The guys put down about 1300 lbs of rebar in the footings and I added another 530 lbs in the slab floor. That is just shy of a full ton, not including the fourteen 16×8 sheets of 6×6” WWR.
They came back the next day to remove the forms and cut grooves in the concrete… However, they didn’t want to cut up in the area where the radiant pex tubing had floated near the surface.
Mistakes:
On the whole, the footings turned out pretty well, and I appreciate that Dysert concrete was even willing to take on this job (many other companies didn’t even call me back after seeing the plans).
However, as a first time General Contractor, I made some mistakes here (just like every other phase of construction).
I should have checked those forms better. As the rule of thumb goes, “put as many stakes as you think you need, and then add a couple more.” We didn’t have enough stakes in many places, especially on the bedroom side where the sand is softest. The bulges are a bit ugly, and they wasted concrete (more volume than needed). In one spot where the form leaned out, it actually affected the surface level of the footing and may give me a bit of a headache later… Oh well, at least these footings will be buried and never seen again. They don’t need to be pretty to do their jobs well.
I did ask one or two guys if the pex tube that I placed looked right, and they just gave me a nod and a grunt… I should have got someone to check my work more closely. Then they would have seen my mistake (not tying them often enough). Things would have been more secure and I could have properly cut the slab to prevent cracks… As it is, I have 3 long (thin) cracks across the uncut portion of my slab…
I should have complained about the level for the grove form. I saw that the east side sagged a bit in the middle, but I thought it would float up or be taken care of some other way… I didn’t say anything and now I need to deal with water pooling in that area. It won’t matter when I am finished the Quonset and grout the groove, but in the meantime, it is annoying. If that water freezes, it could cause damage. It could also rust the bottom of the Quonset steel before it is grouted…
Generally speaking, you need to speak up about concerns and get them addressed before the concrete gets poured… It is too easy to get swept up in the frenzy when there are so many things happening on the site.
At the moment, things are pretty cold for building with concrete. There are ways to cure concrete in freezing cold weather, but the additives often reduce strength and/or corrode the reinforcement, so I am mostly working on planning. I have also pretty busy at work and got going again on my MBA, I am doing a business law class this semester. I go out any time the weather gets above freezing, but there were a couple weeks over New Year’s when I didn’t make it out to the site at all.
