The day after shotcrete on the perimeter walls, we got started on prepping the steel arches and setting them up for another round of shotcrete. This particular apse is special because it will eventually be my office (where I will spend most of my waking hours), and because it needs to be in (along with its retaining wall) before we can bury the garage side of the house. The work was all pretty simple compared to the bedrooms, and I didn’t take much time to stop and take pics, so this post should be short. But first, the video…
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An apse is the semi-circular end of a vault. They are pretty common in earth sheltered homes because they can hold a lot of load, but usually, they are at the back, completely buried. I put mine up front and included a window. Hopefully, it turns out to be a good idea. This apse will also be my office, and I spend a lot of the time on video conference calls, so hopefully, the acoustics are OK. At least my head will be near the window and not near the acoustic focus point.
This is how the guest room looked the morning after shotcrete.
It looks warm enough in the pics, but the temp was probably less than 40 and freezing over night. I left this propane heater in the room to keep the roof warm while it cured.
I was pretty happy with how the mud room roof turned out…
This is the top of the playroom apse. Because it was out in the open, it also needed its own little parapet wall…
Hunter checking on the camera as he flipped the steel arch. He had welded 3 sides of each leg, but needed to flip it to weld the 4th.
Positioned the first arch here and took a quick pic just to get an idea of the scale of the office…
The office apse steel at the end of the first saturday…
Here I am looking quite grizzly, but happy things are working out.
Office apse with mostly just the horizontal rebar.
Michael messing with the camera… He likes moving past it very slowly so it looks like he is moving normal speed and the rest of us are high speed.
Snow stopped our progress for a couple months.
Sherri did most of the lath work during a brief warm spell in February… Sorry, no timelapse.
It was time to shotcrete the central circle of the house. This post is mostly a gallery of pics to tell the story, but first, the video…
Extra time to add the mudroom roof
The rolled steel arches were welded to an angle iron bracket that was sitting on a concrete ledge and had been tapconned the wall. They were very secure.
Additional #5 rebar pegs were also added to the assembly to strengthen the connection between the roof and walls.
This shot shows the full length rebar spaced one ft from the steel arches and the pegs placed every 6 inches. This pic was taken before the last peg was placed over the steel arch.
This wider view shows the span with the rebar spaced no more than 1ft apart.
Kids love to climb.
They air compressor was helpfull for cleaning the dust off the footings just before shotcrete. You don’t want a layer of dust to contribute to a cold joint. You want the shotcrete to bond as well as possible with the footing and hopefully leave no cold joint at all.
Airial view of the shotcrete equipment setup and our formwork.
Michael and Sherri went around to do a final inspection and get some pictures.
In the background of this shot, you can see the strap I used to pull a stubborn wall form plumb.
You can see the electrical conduit, etc.
We wrapped the concrete arches to protect them from the shotcrete overspray.
For this job, I got the articulating lift instead of the boom lift… We didn’t like it as much.
Here you can see the first pass of shotcrete and that a whole section collapsed. They came back and filled it in after the other shotcrete had stiffened up a bit.
Even thought we didn’t like the articulating man lift as much as the boom lift, we did like the lift company. We highly recommend wolverine rental.
The final texture was sort of smooth, but certainly not flat. It won’t matter to much since it will all be covered, and at least it was smooth enough to waterproof easily.
Here they are working on the wall in the mudroom. This is why I didn’t want to finish the roof. But once this was done, I could close it off.
David went to get my camera and move it at some point…
End of day 1…
End of day one and we had the north side mostly done.
The timelapse caught this by accident as Aaron was moving it. All the rest of the pics were a tumble of sky and earth, with this one stuck in the middle.
The nearest neighbors house looks quite nice on this fall day. I am sure the view in the other direction is not as pleasant… Sorry.
With the shotcrete only 16 hours old, we started to strip the forms.
Here you can see a closeup on an electrical outlet. The smurf tube did make a bit of a shotcrete shadow.
Here you can see the imprint of the particle board after removing the forms.
Hunter setting up the camera…
Paxton’s son, probably stretching a bit, after all that bent over welding.
Morning of the final shotcrete day… Still a bit foggy at 1000 ft elevation.
In these foggy pics, you can see the mudroom roof is ready to go.
Over the weekend, I also had time to remove the particle board from the apse parapet.
Parapet after removing the form boards.
If I had completed the span across this hallway, the guys would have had to shoot the concrete upward and probably would not have got the wall as solid.
This was the funniest thing… With the weight of the two guys and the heavy hose, they couldn’t get the basket to top back up again. I appreciated that they just went ahead and did the shoot anyway.
This was the minimal bracing that we put under the mudroom ceiling to provide a little extra support. I don’t know that it was necessary or ever took any load, but better safe than sorry.
This is how the mudroom ceiling looked after pulling away the formwork. Of course, we will plaster over this at some point.
THis is the mudroom ceiling after removing the bracing and boards.
There was just enough decent weather left in the season to prep and shotcrete the walls around the perimeter of the central circle. We had to start with the formwork, and since these walls had simple curvature (rather than compound curvature), we decided to use OSB board screwed to vertical steel studs. Of course, rebar was added in and tied. I’ll get into details and lessons learned later in this post… And there is always a gallery of pictures at the end, but first, the timelapse video.
These MarinoWare steel studs I have been experimenting with are a bit of a mixed success. They are great for holding the formwork, rebar, electrical, etc. And I like to think that they provide some reinforcement for the concrete. On the negative side, the shotcrete crew were not always able to properly encase them and possible voids in the walls along these studs probably reduced the wall strength and provided a path for water to channel. I wouldn’t call them a total failure, but I have decided not to use them in this same way for the central tower. Instead, I will brace that formwork from the outside. I will continue to use these studs for the South wall because the design there has these outside the concrete, supporting the rigid insulation formwork.
Screwing into Steel Studs
Pre-drilling would just take too long and it would probably drive you crazy trying to keep the boards aligned to get the screws thru the pre-drilled holes. Self-tapping drill point screws are what you need. They should be long enough to get thru the form materials (3/8th inch OSB in my case) and still bite in nicely to the steel. In places where you put an extra layer of OSB (such as to thicken the joints), you will need an extra 3/8ths of length. Also, to save money, you want to use the shortest and smallest screws that will work. Finally, the key thing is the head… I recommend the Hex-Washer-Head because it will be held securely by your driver without any slippage or cam outs. Do not buy Phillips head screws, you will seriously regret it.
Personally, I ended up mostly using TEKs #10 x 1 in. Zinc Plated Hex-Washer-Head Self Tapping Drill Point Screws that cost about 4 cents each. If you can get them in bulk, you can probably reduce the price to half that.
Plumb and Braced
For some reason, the camera kept moving on to the next area before we would complete the important job of plumbing and bracing each section of wall. However, that step was important and worth a small section here. The walls had some natural stability because of the curvature, but we still needed to brace them against the force and vibration of the shotcrete and they were not always naturally plumb. On dirt, we could just brace with a 2×2 or 2×4, screwed to a block on the wall and then screwed to a stake. However, for most of this job, we had to brace on the concrete deck and didn’t want to attach the bracing to the deck and risk damaging our radiant tubing… The solution was to place a board on the deck, screw the diagonal brace to that, and also screw a horizontal brace and tie it back into the wall. This worked pretty well.
In one location, the wall was out of plumb and took some serious pulling to try and force it plumb. Some combination of the boards, studs, and rebar was fighting against us. I ended up just using a strap and a come-along to pull it. Part of that strap is still embedded in the concrete wall, but at least it is plumb.
I get a lot of negative comments from people saying that it is “against code” to weld rebar. In reality, the building code has about 85 pages devoted to welding rebar. The code talks about what types of Rebar you can weld (mine has a little “w” on it to indicate that it is weldable), diameters (most welding rules don’t kick in until #7), what types of welds you can do (butt joints are not acceptable), pre-heating, exceptions based on engineering approval, etc. I was going to get into it a bit here, but it is probably better to just suggest you read up on it yourself.
While I agree that the heat treatment that comes from welding does influence the ductility and other material properties of the steel, in certain situations (some of my situations), it does make things much better. I know what I am doing, everything is inspected, no need to worry about it.
Here is where we put some of the pics we took during this period…
from time to time, I’ll just take a photo of my screen so I can have the measurements handy in my phone… Some times it is faster than trying to transfer a proper screen shot…
The Hex Head screws are much much better
For us, this build is pretty focused work. But while we are out there, the kids will often find time to play or read a book in some odd place.
Working on the side wall in the guest room. We had this one shot from the kitchen across the basement stairs.
Me setting up the camera in the kitchen…
I think I may have kept too many pics of David setting up the camera…
Sherri gets goofy some times…
Joe working on the dining room wall.
David Setting up the camera. He likes this job.
Here my father is working on the wood forms and my mother is tying rebar… Probably not the retirement they expected.
Sliding the rebar into the short wall section.
For this little side wall, we put in all the rebar pieces and then cut them down to size.
David setting up the camera for a shot
David was climbing around on the tower steel and took this interesting pic of Hunter walking thru the site.
Another shot of the playroom apse before it got started. You can see all the steel arches leaning against the rigid insulation in the background.
I separate out these jobs, but they often overlap. On this day, I was working (For ANSYS inc) from the site because the stucco guys were working on the garage. In the evening, I probably switched to welding the playroom apse or something like that.
I originally set everything up around this middle post, then I welded the outer edges in place.
To form the apse, I had to weld the thicker rolled steel arches to the thinner galvanized steel studs… It doesn’t have to hold forever, just long enough to be encased in concrete. It took a little practice to be able to weld the different materials reliably. I did little patches like this ever few inches along each edge where they met.
This looks like it was from my timelapse, but the rest of the video was lost… It happens sometimes.
This is one of those pics that happens when your 10 year old is just walking around with a camera.
Welding the rebar
apse steel ready
Apse steel from above
Outside of the guest-room wall. We shot the walls from the outside to try and avoid messing up the deck.
The inside of the guest room forms.
We try to avoid it, but occationally we are all working within a very narrow distance of eachother…
For some reason, Hunter likes to pose for the timelapse… Just while he is walking by in the middle of the shoot. The easter egg photos are mine now.
Friends playing while their parents helped out…
The north side, ready to shotcrete.
This gap between the back of the kitchen wall and the Quonset hut will be filled with a lot of earth.
This pic is trying to show that I cut away the fox blocks and drilled the horizontal rebar into that wall to tie everything together structurally.
The connection between the guest room wall and the mudroom…