Autoclaved Aerated Concrete (AAC) walls can be formed in thicknesses from 4" to 14", and blocks come in various sizes; hand stack blocks (8" high by 24" wide by wall thickness) and jumbo blocks (24" high by 32"-40" by wall thickness) This house was built using 12" thick exterior walls and 4", 6", & 8" interior walls. The majority of the house was built using jumbo blocks, but the smaller hand stack blocks were required for some areas.
Once the foundation was poured, we began building the interior and exterior walls. Using a construction laser we were able to find high and low points of the foundation, which varied by only 1". The first layer of block is called the leveling course. We used 8" high hand stacked blocks for this course. They were mortered in place using Type S Mortar which allows for a 3/8" to 3/4" mortar joint. We adjusted the height by varying the mortar thickness where we could. Once the entire leveling course was in place and the mortar was dry, we leveled the entire surface with a special AAC rasp. (AAC actually cuts very easily, so, many wood working tools could be used for this purpose. Later on in the building process we discovered that an angle grinder with a concrete grinding disk works very well for this.)
We were then able to begin placing the jumbo blocks. Each block weighs approximately 200 lbs. Much too heavy to lift by hand, so, we used a self erecting tower crane to lift them into place. The crane can lift up to 4000 lbs. I know that may seem excessive for 200 lbs., but set up at the center of the west wall, it could reach all areas of the house, and was used to lift everything from block to concrete buckets to steel I beams and logs.
The AAC blocks were mortared together using a thinset mortar which leaves a mortar joint of about 1/8". A special notched scoop trowel was used to spread the thinset into place. The block was lifted using a special block clamp that releases as soon as the weight is positioned on the wall. The AAC used for this project has a compressive strength of about 500 psi, however, a grid of 3000 psi concrete was created throughout the wall system. This was achieved by drilling a 4" core in each block that was positioned at a corner, a window, or door. These cores with #5 rebar were then filled with concrete.
Door and window headers were created by placing U-blocks over the openings and filling them with rebar and concrete. Before the U-blocks were filled with concrete, they had to be supported by temporary wood frames. These wood frames were easily held in place with 4" wood screws into the AAC. Openings greater than 3' require 2 rows of U-block or 10" of concrete. Openings less than 3' only require one U-block or 6" of concrete
We continued mortaring block in place up to the ceiling height, where we installed a course of U-block filled with rebar and concrete all the way around the building. Before the concrete was poured, 4" openings were cut into the U-block and J-bolts were bolted to ledger boards that would later hold up the interior floors as well as exterior decks. The original plan was to use pre-cast reinforced AAC panels for the floor as well, but the shipping costs were prohibitve. So, the floors were built using a typical wood framing method of joist hangers attached to the ledger board holding TJI's, then sheathed with 3/4" plywood. Because this building process took such a long time, we covered the wood sub-floor with an EPDM roofing membrane to protect it from weather.
We continued mortaring blocks in place on the exterior, but the interior walls had to be layed out slightly different. For the main level, we layed out the interior walls by placing 3/4" thick strips of plywood around the footprint of the walls and filling them with self leveling concrete. From there we continued mortaring blocks in place as usual. For the upper level we decided to install the interior walls in a slightly different way. Once we had layed the sub-floor and put the EPDM in place, we layed out the interior walls by placing U-blocks in position and filled them with rebar and concrete. We then proceeded mortaring blocks in place as usual. When the house is dried in, the EPDM can be cut away at the interior walls and the portion under the walls will remain as a vapor barrier between the wood and AAC.
We are currently working on the last course of jumbo blocks and door and window headers. The next step will be the roof. Stay tuned!