Thursday, October 27, 2011

Precast and backfill in pictures

The plank is set in place by the crane and positioned manually.  The joints between the planks are filled with grout to lock them in place.  The gray tube is a foam rod to prevent the grout from leaking through to the basement.  The round dots at the bottom between the holes are the tension cables.  

The stairwell is formed by installing a hanger to hold the end of a shorter precast concrete plank.

We have backfilled as far as we can before we finish the concrete floor.  The Spiderlath around the basement egress window will show in the window well and be in the same plane as the wall above it.

We laid out the wall and cabinet locations, and tied the radiant floor system to the wire grid.  We will pour a 3" concrete cap over the precast to encapsulate the radiant floor piping.

Precast is set and backfilled

In spite of the fact that I have been out of town for several days, this has been a remarkably productive week.  Maybe I should draw some conclusion from that.   

The precast concrete plank was set on Friday.  This is always exciting because it seems so much gets done so quickly.  Precast plank is concrete that is extruded from a machine on about a 300’ long flat table.  You can see in the pictures the embedded steel cables at the triangular section between the hollow cores on the bottom.  It is hollow to conserve materials, and make it light weight enough to transport.  The system functions as a series of linked I-beams. 

When the concrete is fully extruded, they stretch the steel cables and tension them.  The concrete hardens, and the cable tension is released, tightening up microscopic cracks that occur in the concrete drying process.  The 300’ extrusion is cut up into the lengths for specific projects.  This is called post tensioned concrete, and is very strong.  We can clear span the entire basement without having to pour a footing, place columns or center beams to support the floor.

The decision to have a concrete floor is to create thermal mass.  We can store heat or “coolth” in the thermal mass of the concrete.   It retains the temperature for long periods of time and releases that temperature slowly.  This strategy will be useful in the winter when the sun is at a low angle through the generous southerly windows.  The sunlight will penetrate the windows and charge up the heat in the floors, storing it for the night.   The inverse is true in the summers.  We can open the windows on cool nights, and store the “coolth” for radiation in the daytime.  That’s the theory anyway, and we will soon get to put it into practice.

When the precast was set, we installed a wire mesh on top of the precast and zip tied the radiant floor tubing system to it in preparation for pouring a 3” concrete cap over the top.  The tubing is zoned by room to provide maximum controllability.  This will encapsulate the tubing in 13” of concrete, and we can heat or cool the slab as we need to adjust temperature.  More on that in a future blog.

We added a single wood frame wall on the east wall of the garage to allow for the early installation of the electric meter and underground wire service for electric and phone.  The underground phone wire was to have been run this afternoon per instructions given over the phone.  The electric meter should be installed and inspected later this week.

We were fortunate to be able to backfill the foundation walls this week with very wet weather.  The sandy soils on the site are no impediment to backfilling the foundation, and assisted in the compaction of the soils after such a dry fall. 

We had a pretty big setback with our intent to install cement stucco on the exterior of the house.  We had planned to practice on the area below grade so that we might be proficient at the application by the time we got to the finishes that showed.  The compressor we were using is too big for my 6500 w generator, and we (ok I) roached the motor.  We have had to abandon the plan to practice on the foundation, in favor of maintaining the schedule.   We may end up with either really thick stucco on some walls as we master the application skills, or end up hiring it out to a competent contractor. 

The plumber completed his underground plumbing and is waiting for an inspection tomorrow to backfill his trenches.  He was a great help to me (as I choked back my frustration with the compressor) when he brought his small hand held compressor to help put a test charge on the Pex tubing for the radiant floor system.  We found a few leaks at some of the joints, which we fixed, and the system held pressure the rest of the day.  It was great peace of mind to leave on my trip knowing we had that hurdle behind us.

Next week we will be able to install the rest of the underslab insulation on the bedroom wing, install the radiant floor system, and pour the slabs, weather permitting which will be a big milestone.  I have a week of cure time after that before we start the framing.