Monthly Archives: October 2016

Another round of shotcrete forms


Posted on October 15, 2016 by

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.

The Video

Extra bits

Steel Studs

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.

Welding Rebar

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.

The Gallery

Here is where we put some of the pics we took during this period…


Lath and Stucco


Posted on October 9, 2016 by


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.

The Video

Lath overlap

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.

The window

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.

Future Stucco?

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.