After welding the legs on the steel arches, it was time to assemble the bedroom structure. The basic elements are the steel arches, placed on the bases and connected by rebar. The bases were just 3/8th inch thick steel plates with #4 rebar pegs to hold the plates in place. The pegs were welded to the plates and the arches were welded to the plates. Small pieces of rebar were welded to connect perpendicular arches to stiffen the assembly. Horizontal rebar was tied on first, just to get things in place, and then that rebar was welded to the structure so it would be safer to climb on. For the vertical rebar, we started with 5/8ths inch holes drilled right into the footing. I curved each piece of rebar by hand and dropped the straight end in the hole. We then tied (and eventually welded) each vertical piece to the rest of the assembly.
Some of the little side stories are best told with captions, so here is a gallery
You may recall that we had steel arches rolled (curved with big rolling wheels) into arches. However, these arches needed legs welded to them. They also needed a way to fasten them to the footing and a way for them to hold rebar.
The first two of those ideas are looked at in this video. Details and how we attached the rebar are included in this post…
Welding the arches
The steel fabricators that rolled my arches are also expert welders (among other things). I did get a quote to weld the arches together, but it was $6000, and that was just for the 30 arches on the bedroom side (not the other arches in the radial vaults). That is about 100$ per leg welded on, or, assuming 4 welds per leg, 25$ per weld… And that doesn’t even weld the arches to the feet or attach any rebar. I assumed the quote meant that they wanted me to learn to weld, so I bought a cheapwelder on Craigs list (a couple hundred bucks got me fully setup) and practiced so I could do it myself.
The arches arrived on site in early may. All the half circles had been cut to 180 degrees. Some of the larger ones were actually segmented in 2 or 3 pieces so they could more easily be delivered. The Elliptical arches were not trimmed (I would need to use my template).
My sister came out to help and we spent the morning practicing and getting the settings right on the welder. When it came time to weld the real arches, we first needed to assemble the pieces together and we needed the legs to be parallel. We did this by setting things up with equal diagonals and then building a brace jig, like a truss, to keep things aligned correctly. The jig took a few extra minutes to build, but we had a number of arches of each size, so we were able to re-use it and save a lot of time later.
Early in the welding, we were very serious and wore all the gear and clamped the jig on again after flipping the arch to weld the bottom… By the end, I stopped wearing the jacket, switched back to sandals and didn’t worry about the jig after the initial welds were in. Actually, not wearing all the protection helped train me to be a better welder. There is nothing like hot metal burns to teach you how to weld without sputtering.
I did, however, keep wearing the gloves. I found the best way to weld was to old the gun with both hands and to rest one of them on the work to stead the gun. The other hand could then control the gun with good fine motion control.
I also learned the importance of keeping that shielding gas concentrated around the work and how sensitive the welds were to the settings on the welder. If the wire speed was too fast or two slow, welding became difficult, and experience taught me to quickly realize that I needed to adjust the settings up or down for the conditions.
Along the way, a number of people stopped by to try their hands and welding. Only one of them had any prior experience (and he taught me a thing or two).
My 10 year old also got a few good welds in.
Of course, I ended up doing most of the welding by myself. I could weld and move the small arches; but larger arches were very awkward (and just a little bit heavy), so I relied on my wife, Sherri, to help move them. At one point, Sherri tripped (on a piece of rebar) and lowered the arch as she caught her self, but the welds were still hot, so she got a nice burn on her shoulder. We gave the steel lots of time to cool after that. I started staging things so that instead of welding all the arches of the same size in a series (where I would need to move arches between each set of welds), I would weld a set of “nesting” arches (of various sizes) that I could weld all at once and leave on the ground until Sherri could come out to help me flip them all.
Steel arch bases
As I have said before, my best example for this sort of construction is “Formworks.” Check out their Facebook page for lots of great pictures. These guys have lots of experience and they know how to make the process doable for the do-it-yourself market. They have features like brackets that you bolt to the ground and then the steel arches fit into them and are bolted in place. They also have Z clips pre-welded to the sides of the arches so you can easily place rebar and just hammer the clip to lock it in. The catch is that all this convenience comes at a steep price. I needed to come up with a much more cost effective way to get the job done.
I considered buying scaffold feet (as I had for the tower columns), but they were about 5$ each and would need to be bolted down with 4 bolts in 4 drilled holes. That would mean careful alignment and lots of time drilling.
If I stripped the requirements down, I needed 2 things. 1) a bearing surface to spread the weight of the steel out so it wouldn’t penetrate the footing. 2) a vertical pin to keep the leg of the arch from moving laterally. There was no need to prevent rotation, so i really only needed one hole, and there was no need to prevent lift, so I didn’t actually even need to bolt the feet down.
My final solution was just a 4×4 inch steel plate, 3/16ths of an inch thick, with a hole in it. I would use a piece of scrap rebar as a pin to keep the plate and the steel arch in place. I got quotes on getting these made and was told hundreds of dollars. I forget the exact ridiculous number, but it worked out to nearly $8 dollars per drilled hole. So I decided I would take care of this myself. The savings would pay off my drill press for the second time.
To position and assemble these bases, I drilled a single 4 inch deep hole in the footing and put an 8 inch long piece of scrap rebar thru the hole in the plate and into the hole in the footing. I then welded the rebar to the steel plate with 3 tack welds. I didn’t grout or epoxy or bolt anything. To set the arch, I would simply put the end of the steel tube over the rebar, adjust the location a bit and then weld it to the metal plate.
This solution was cheap to make, and quick and easy to install. The only catch was that I needed to weld each connection… This is a pic of a place where three of these bases were near eachother, so I used a “double” plate and welded it to the adjacent “single”.
Attaching the horizontal rebar
Placing vertical rebar is easy, you just drill a hole in the ground. Attaching horizontal rebar to smooth steel tubes is harder. If you tie it, it may just slide down. Welding everything in place as you go would probably be too time consuming and would require more hands than I usually have.
I decided to try and find a cheaper way to replicate the basic idea of the Formworks Z brackets. I started by looking at prices of various channel steel that would work. As usual, buying actual raw materials is not the cheapest way. I found that I could get steel shelving pieces (made in China) for the best price. I would just cut them into 3/4 inch slices and weld them to the frames myself.
I prepared about 5 of these, but when I added up the cost of materials and my time (at only 10$ an hour) for slicing and grinding down the excessively sharp edges, they came to about $0.50 each. And that didn’t even include the time to weld them to the frames and I would have hundreds of these.
Another idea was to weld S hooks to the sides of the frames so that one side of the hook could catch the rebar. I bought a few of these for about $0.25 each, but couldn’t find a good bulk price. I found that they were easy to weld in place, but the opening was a bit tight and I would need to hammer them open a bit to better receive the rebar.
Then I decided I could just buy a big box of nails ($0.01 each) and weld those on at an angle to catch the rebar. Then I could just hammer those over to hold the rebar firmly in place. But the welding task was still daunting and my wife thought they created a real hazard on the job site. “You’ll poke your eye out kid.”
Then I decided to break it down to its simplest concept. I couldn’t just wire the rebar to the smooth vertical steel tubes because it would just slide down. All I needed to do was stop the sliding. I decided to notch the steel with my grinder. I made the notches every foot (my horizontal rebar spacing) and made sure that the tie wire caught the notch… Problem solved. The cost was very small (one $2 disk could make all the notches for the project) and no welding was required. Actually, my friend Aaron brought me a 10 pack of metal cutoff disks that he had for some reason, so it was all free to me.
Mistakes were made
Perhaps in my misguided effort to be a good host, I made a few mistakes by setting up a few early arches without first carefully laying out the locations of all the arches. This meant that my first few arches were welded in place before I noticed that I had some how made a 5 degree error in placing the first one… I ended up “adjusting” the other base locations to try and sort out the locations, and it will all work out, but without the crisp straight lines that I originally thought I wanted.
German vs Spanish
Online, you can find many examples of “German” earth shelters where the construction is very precisely planed out and executed. Even if they have “free form” shapes, they are constructed very precisely to the specified forms. You can also find many “Spanish” examples (including many in Germany ;^) where the builders basically hand formed the rebar arches as they went, perhaps based on some rough sketches, and ended up with a much more organic free-form design.
I had started this build with a more “German” ideal in mind. I used Marino Ware studs to get perfectly vertical walls. I had the steel arches rolled by professionals to exacting specifications. The design its self was very euclidean geometric so that I could precisely work out all the angles.
But as it is going up, small mistakes (mine and others) and approximations are adding up and it is becoming more and more “Spanish”. My epiphany was when I realized that this was because I was the one making many of the approximations, and that, perhaps, I was a bit “Spanish” in my construction. I also decided that it will still all work out, even if it ends up looking a bit more organic rather than purely geometric.
In the next post, we will finish erecting the steel arches and start putting up rebar. I just couldn’t fit it all in to one video/post
As part of my build, I wanted to experiment with a variety of different construction methods, including ICFs.
ICFs are “Insulated Concrete Forms” that you can use to build a very well insulated wall. They stack like lego and include strong high density plastic (HDPE) inner supports that hold the sides together while the concrete is being poured. This inner web structure is also used to position and support the rebar and the portion embedded in the polystyrene acts as furring strips for attaching things to the wall. After the concrete is poured, the forms are just left “in place” as insulation.
In addition to the 4 inches of polystyrene insulation, we will be adding 6 inches of concrete that will give the wall mass to retain heat, “dynamic R value“.
The front and back of my garage (Quonset hut) are flat walls that needed to extend past the Quonset hut and perform double duty as a parapet retaining wall, all without any complicated construction or difficulty attaching insulation. ICFs seemed like the perfect choice for this application.
The final setup
Installing the Fox Blocks ICFs was pretty easy, as you can see in the video. Lessons learned are included in this post.
I looked at many different ICF companies and carefully considered their various advantages. Some fold flat for easy shipping, others have longer or taller blocks or come in separate pieces that can be assembled in a variety of different ways. Cost of materials and installation were also a concern. In the end, Fox Blocks was my first choice. For more on why, see this earlier post.
The blocks cost about 20$ each and I was able to buy them directly and install them myself without any fancy tools or equipment (or skills). A regular concrete block wall (CMUs) would have been cheaper, but would have been much more work and required much more skill. I would also have needed to insulate it, so maybe not even that much cheaper.
The Story (lessons learned in orange boxes):
We started out by measuring and marking all the locations for doors and windows right on the concrete pad/footing. From this, we could easily mark all the locations for the rebar. We drilled half inch holes 3 inches into the concrete at each rebar location.
The Fox Blocks stack very easily. We also use the “Fox Clips” to clip the blocks together horizontally and vertically. After each layer, we added the horizontal rebar. My engineer specified one piece of #4 alternating near the front or back of the wall each 16 inches. The internal web of the Fox Blocks had notches to hold the rebar so that we didn’t even need to tie it in place.
The lego bits (that Bonnie insists are called “nubbins”) are every 2 inches and the blocks can be stacked upside down or back to front, but you definitely want to line up the internal webs so that it is easy to clip things together vertically. It also makes it easier to attach things to the outside of the wall if the webs are all lined up.
In the first section of wall, we had a T section for 3 levels on the back. So when Bonnie got to the 4th level, it was a bit tricky to trim a block for that transition and you can see her trying a few different things (stacking and unstacking and then trimming and re-stacking) to get all the internal webs to line up.
After the wall was mostly up, we started dropping in the vertical rebar (half inch) and then using a hammer to tap the ends of the rebar into the half inch diameter holes in the footing. These 3 inch deep holes were enough to hold the rebar vertical within the wall, however, in many cases, I still wire-tied the vertical rebar to the top horizontal rebar just to keep it all where it was supposed to be. This vertical rebar strengthens the wall and also helps the later layers hold across the cold joint at the top of this section of the wall.
When initially constructed, the blocks are securely attached to each other, so you have a monolithic form. The vertical rebar keeps it from moving very far in any direction, but it is still very loosely positioned and not plumb. You can see it moving around a lot in the video. The wall will need to be plumbed and aligned as a final step.
We screwed 2x4s into the sides of the bucks. It is very important to screw them in where the plastic reinforcement is. In those locations (which act like internal furring strips), the screws bite in nicely and hold well. Anywhere else, and they will just pull right out of the polystyrene. these strips are hidden under the polystyrene. Fortunately, the blocks are clearly marked with the words “Fox Blocks” along the furring lines.
Unfortuneatly, I was not clear enough when working with my friends/family and assumed they all understood how the plastic strip locations were marked. When their screws would not bite in, I would say something helpful like, “You need to make sure you screw it into the FOX BLOCKS.” and I would point to the line that said “FOX BLOCKS” vertically on the side of the block. I would even screw one in for them to show them how it worked. They would nod and smile, but were actually thinking, “Yea, I am screwing it into the Fox Blocks, what did you think I was doing? But its not working for me!”
It also didn’t help that we were (at least initially) using screws that were not threaded far enough up the shaft. It was fine for the 2x4s, but when used with the thinner boards, the threads passed all the way thru the plastic and spun without really tightening up. This caused quite a bit of frustration for Zack who was in charge of putting up the thinner boards.
Once the 2x4s were in place, we positioned and plumbed the ends of the walls using bracing and stakes to fix them in place. Then we stretched string between the ends so we could align the rest of the wall. Section by section, we used a level to plumb the wall and the string to align it. The bracing at each section was individually staked.
This turned out pretty well, but I didn’t factor in potential movement at the bottom of the wall. I had not fixed all the degrees of freedom and had relied on friction and the weight of the wall to keep the base where it was. Of course, an ICF wall is relatively light and the strong winds shifted it in the 2 days between setting it up and the concrete pour. I ended up needing to make some last minute adjustments. Next time, I would also do something to secure the location of the back of the wall along the bottom edge.
Holes for the windows are cut out of the Fox blocks. We used “Fox Bucks” to frame around the windows. Fox Bucks are similar to the Fox Blocks (Polystyrene molded around an internal webing of tough HDPE plastic), but without the “snap together” feature. Instead, they must be taped into place and then the seams are held together with externally applied boards screwed in on both sides (the block and the buck). Again, it is critical that the screws be in the plastic within the Fox Bucks, but the plastic fills pretty much the full sides, so it is hard to miss.
Not everyone helping understood that the concrete would be exerting hundreds of lbs of lateral force to push the bucks out and that tape and a couple screws would not hold them. I understood, but my big mistake was not fully inspecting (I was too distracted) that the boards were screwed into both the bucks and the adjacent Fox Blocks every 8 inches or so. This lead to some blow outs and additional work down the line. More images of this sort of mistake in the gallery at the end of this post.
The Fox Bucks are also used at the top and bottoms of the windows. When used as window sills, we had to cut holes to allow the concrete to be poured in. We also sloped the sills (by trimming the front of the underlying blocks) so water would drain off.
The full height of the wall is 12 blocks tall, but we only setup the first 4 levels because we wanted to be sure that the concrete would consolidate all the way down in the forms. If we were more experienced, we may have tackled a deeper pour and got more done at once. But as it was, I was glad we kept this first one simple. Stopping at 4 levels also meant that I could let the first part harden before I added concrete across the tops of the windows and garage door, which probably saved me a disaster. The cold joint that will occur is bridged by the vertical rebar.
The final steps were to place 6 mil plastic to separate the coming concrete from the Quonset hut steel and to spray foam some gaps and along the bottom of the wall. It not only fills gaps to keep the concrete from leaking, but works as a very effective glue.
The ICF wall was inspected and approved. Keep in mind that the inspector checks basic things like if you have Rebar in place, etc. He does not check for every screw. As the general contractor, that was supposed to be my job.
On the day of the pour, we also planned to take care of the basement floor and the concrete ribs while we had a pump truck on site. I was actually running on fewer than 4 hours sleep and still frantically finishing some final details on the rib forms when the concrete trucks were rolling up. I should have been inspecting the forms. Is that enough foreshadowing for you?
Since I had experienced concrete guys on site to take care of the floor, I also asked them to help with the ICF walls also. To make sure that the concrete was properly consolidated in the walls (without air pockets, etc.) I had bought a 5 ft long concrete vibrator for $99.00, which I would recommend to anyone doing similar work.
As soon as the concrete started filling the forms, the end started popping open. It was immediately obvious that one of my helpers (who shall remain nameless) had not really understood that concrete would be trying to push its way out of these forms and had not secured things nearly enough. For instance, on the first end, he had only fastened the top and bottom of the board. Hundreds of lbs of lateral force were pushing out the middle and we had to scramble to brace it. The windows bucks held up well, but then one side of the garage gave out and a few hundred lbs of concrete spilled out while we frantically grabbed scrap wood to brace it. Seeing that not nearly enough screws had been used, I ran ahead of the concrete hose and frantically added more to the other bucks.
We made sure that the forms were not filled all the way to the top and we roughed up the top surface of the concrete so that the next layer would grip well across the cold joint.
It all happened very quickly… So quickly that, for the time-lapse, I had to slow it down by 50% so I could fit two sentences into the scene.
Once the day was done, I had time to think about my mistake and plan to do it better next time. There will actually be several more phases and I will need to wait until all the rib forms are done before I can complete the garage and put another ICF wall on the front of it.
Here are some pics from the day with descriptions. Thanks to all those who helped me out.
The Fox blocks arrived in light weight bundles of 12.
Dimensions on the computer model
The final setup
Michael playing tag (caught by the time-lapse cam)
Zack and David working together.
Here I am wire tying the vertical rebar to the horizontal
Bonnie trimming off the end
The Fox Blocks are light weight and easy to handle
We also put in a little side wall for the Mud room
No screws holding in the Fox buck at all…
Here you can see why the middle bulged out. It would have blown, but we braced it in time.
David inspecting the damage
Clips hold the blocks together
Here you can see “FOX BLOCKS” written vertically, aligned with the internal plastic