Placing the walls

Once the foundation has been laid, complete with rebar, it is time to place the block for the walls. I mentioned elsewhere the various possibilities for building curved walls: Hay bales, Durasol block, Performwall/Rastra etc. . I chose to use PerformWall due to it’s local availability, use of recycled polystyrene, insulation value and shape. I purchased 106 pieces of 12″ thick by 15″ wide by 10′ long block. I was able to position these blocks upright on the foundation, thus creating a circular polygon with 106 15″ sides. I figured that this was as close to a true circle as I was going to come given the material choices I had.

The photo below shows the makeshift crane we devised to move the ICFs around and gives an idea of the size of the blocks. The engine hoist used for the crane saw duty attached to a 1949 Studebaker truck for large scale moves, and attached to a 3 point hitch on a 1951 Ford 8N tractor for moving and placing individual blocks. It was an invaluable tool.

Stacking the ICF's with a makeshift crane

The blocks weighed 110 lbs (50kg) each, which at 10 feet (3 meters) long made them difficult to move with only two people. I wanted the joints between the blocks to mate closely and so made a jig which I attached to a chainsaw which allowed me to shave roughly 1/2 inch from one corner for the full 10 foot lenght of each block. The blocks when placed tightly side by side then formed the circular shape of the outside wall. I then cut each block in half to 5 foot lengths for ease of placement.

Placing the first blocks on the foundation

This picture shows the first two 5 foot tall blocks being placed on the footing. The rebar sticking out of the footing is clearly visible. It is placed to penetrate the concrete cores at 30 inch intervals. Matching rebar is placed in these core holes prior to pouring the concrete to connect to the next course of block. The blocks are glued together using a polyurethane foam glue and held in place while it cures with large steel staples, which we borrowed from our supplier, SolSource.

Moving around the circle with the block

We continued placing block around the circle, cutting the block to length for door and window openings. Rebar had to be placed every 30″ in the block both horizontally and vertically. It was thus necessary to stop every 20 blocks or so and thread rebar through the horizonal cores before continuing on.

Once all the rebar is placed, any bracing in place and the rebar inspection passed, it’s time to call in the concrete truck and pumper, Or if you are a masochist, load up on the concrete mix, sand and rock and get to work. We did it both ways. The first course of block was filled with concrete from a truck and pumper setup. This was difficult because most concrete guys know more than you do, including how thick the concrete should be. Unless they’ve done this before though they are going to be wrong. Convincing them of this is almost impossible. For PerformWall or Rastra, it’s necessary to have a 9″ slump, which is relatively wet, so the mix flows through the horizontal core channels. A normal mix will not do this. It took quite a while and several badly poured cores before they added enough water to the mix to get it right.

The first course poured, showing vertical rebar and stapled second course

The photo above shows me with the first course poured and starting on the second course blocks. The staples are visible on the upper blocks holding the block in place as the glue cures for an hour or two. As before, we went around the circle matching up door and window holes and striving to maintain a plumb wall surface and line up the block properly. This is much easier said than done.

Outside view of wall showing brick ledge

We had purchased a large amount of brick that we were planning on using for the outside facing of the house. In order to use them it was necessary to pour a ledge that sat on the footing all the way around the house. The above photo shows this with particle board form work spaced out from the blocks about 5 inches. Rebar was placed in this ledge wall as well. It is also barely possible to see the brick ties (or at least their shadows) sticking out from the first course wall. The ties were placed such that one end was embedded in the vertical concrete cores prior to pouring. While necessary for tying the brick to the wall, these are hazardous as they are sharp and stuck out from the wall for many months. Bending them up helped us avoid injury.

The windows and doors were a challenge. It is necessary to have a strong lintel over each opening. We did this by purchasing the performwall in 2″ thick sheets and making the lintels of solid steel reinforced concrete. This can be seen (without the rebar) in the photo below.

Formwork for over windows

It should be noted that all wood that touched concrete was pressure treated to resist rot and any nails or bolts that were embedded in the concrete cores were galvanized to resist rusting. Rebar was placed as before 30″ on center vertically and horizontally. J bolts were placed in the top core during the pour to hold a sill plate. Multiple pieces of horizontal rebar spanned every door and window opening. The final pour was done by hand after the required rebar inspection.