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…
The style of the home is something my wife and I are calling “Modern Tuscan“. To us, this means a stucco and stone exterior. While the majority of the Quonset hut will be buried, the Fox Block ICF endwalls would be visible (and prominent) and need to be stuccoed. But first, we would need to attach lath to hold the stucco. Since the work was pretty standard, I decided to hire a professional to take care of the actual stucco work. This is the story of how that all came together, but first, the video.
As always, this is a journal of my progress, not a “how to”. I don’t always do things the right way at the start, although I do usually learn from my initial mistakes. For the lath, I read about attachment details like how often to put screws in each direction (and then I exceeded it), but I didn’t pay too much attention to the part about overlapping the lath and just butt jointed everything so the surface would be flatter for the stucco. Probably I was also thinking about saving on lath. At a later point, I changed my mind, so the later pieces are properly overlapped… Either way, the professional stucco guys said we did a good job and only needed to add some J-pieces to form the bottom edge.
With such a large and prominent wall, I knew I needed a window to break up the space. Personally, I think a square window would have looked stupid, so I bit the bullet and budgeted for a nice round window. At least I went with a standard diameter window so it wouldn’t need to be custom.
However, when I finally got to this stucco stage, I wasn’t ready to order the windows. I want to order them all at once to get the bulk discount, and I wanted to build all (or most) of the bucks before I order, so… In the meantime, I decided to go with polycarbonate Lexan. This is pretty basic stuff that you can buy from Home Depot less than 1/10th the price of a window. The R-value is also pretty similar to a double pane window. I figured it would at least give us a temporary solution that would keep the inside dry over the winter.
It ended up looking so good, I might just decide to keep it this way. We will see how well it holds up to UV. Obviously, if it yellows or cracks over time, I will switch to glass. But it did claim to be “UV stable” and has looked fine so far, so I am optimistic.
Still, I wanted to make sure that the window opening was ready for proper glass so that the stucco edge would all be done correctly. We used wood strips to form a curb, and then put two layers of the tar paper to protect the wood and then a strip of lath to hold the stucco. Lots of screws…
Getting a Contractor
I have had many struggles with getting contractors to work on the more unusual parts of my build, but I was surprised to even have trouble getting something as basic as “stucco over ICF”. Very few of these companies advertise properly, probably because most are kept busy by professional builders and are not actually looking for work. Eventually, I went to the stucco supplier and asked for a list of names and recommendations. One of those paid off, but even then I had to wait quite a while to fit into the schedule.
Of course, the contractor, Hoffman Plastering, did a great job in terms of how nice and flat the wall was (they certainly had to compensate for my less than professional ICF job). Their classic worm finish was also excellent.
However, in the months after the stucco was applied, we did get a bunch of fairly obvious cracks in various places and we have not been able to get them to come out and take a look. On the phone, they said that it was probably my fault. Essentially, they blamed the copper cap and said that water probably got behind the stucco and froze, but I was able to find pics showing the start of the cracks before the first freeze, also the cracks look more like ones that are caused by expansion and contraction of the stucco its self. Basically, I imagine that if the south wall expanded in the sunshine, this narrow region would be the highest stress concentration and the most likely to crack. The inspector thought it may have been that the top layer was applied too soon after the brown coat. The contractor may have rushed that step because the work was done in October. The cracks are not wide enough to get the edge of a coin or screwdriver in there, but are still concerning. The conclusion of this story is still on hold, but I should probably do something before winter when water might actually get in thru those cracks and cause further problems when it freezes.
I wish I could hire a contractor to stucco the rest of it. Their work was excellent (other than the cracking) and the quote to handle the rest of it was probably fair per square ft. The problem is just the large number of square ft required. The majority of the cost is the professional labor, the actual materials are a very small fraction of the cost. Therefore, I am guessing I will need to do it myself. With any luck, my skills will grow quickly.
As per usual… A collection of pics related to the lath and stucco.
Lath is ready on the north side…
Working with Hunter Mitchell often made me smile.
A view thru the Polycarbonate Lexan window
The window ready for stucco
I put a septic hookup on the front of the house for friends with campers.
This was the stucco setup. Scaffolding ready in the back and a stucco mixing station in the front left.
I took pics of the ingredients. Basically, it was just cement, hydrated lime and masonry sand. I’ll probably have to do this myself next time.
The bags of hydrated lime looked pretty old ;^)
The stucco sample. I would say it looks pretty much exactly like the final work.
Scratch coat near the ends of the walls.
Scratch coat with the light base.
Scratch coat near the north garage door.
Scratch coat on the north side
Since I couldn’t come out (busy working to pay for the stucco), Sherri and Boys would go out to check on things and set up my camera.
Sherri and David posing while they set up the camera.
The wide angle GoPro always makes things look different.
Brown coat, first 7 ft.
Hoffman plastering did a great job with the stones.
Stone arch is in. Note the stones are not really wedge shaped, but it still looks good.
Stone arch is in
A little progress pic of the brown coat, scratch coat and final stone work all in one shot.
Brown coat finished on the front.
This is a section on the north side by the garage door that was still only scratch coat 3 days before they were totally done. I suspect they rushed these last steps and the result will be that the final stucco will crack along with the base coat instead of being applied after it cracks.
This ugly spot will be covered over by window trim, but I wanted to show you how the guys from Hoffman plastering went the extra mile. The back wall had some issues with being plumb and straight near the rear windows. I thought it was just the way it was going to be, but they just went really thick (~2 inches) until they got it all nice and plumb again.
Suddenly, final stucco
Final stucco coat
The final job looked really excellent.
Stones above the door.
A close up of the top of the column between the stones. The white patch is just the electrical box for the lighting.
Final stucco near the round window. They did a great job on that edge.
A close up of the final stucco
A little while later after adding the lights and copper trim… (notice cracks are already starting to form to the left of the light)
The skid steer just barely fits under the stone arch… I hold my breath every time I go in or out.
Cracks started to firm. Here is a pic with my hand for scale. This is on the north side.
On the south side, the main cracks were across this narrow space between the corners of the doors and the outer edge. I can imagine that this is due to expansion finding the weakest part to crack…
Similar geometry on the South West corner leading to a similar crack.