Wednesday, July 7, 2010

Pouring the footings

We passed our inspection at 10:00 am and confirmed the will call on the concrete and pump for 12:30 pm. I ordered a 3/4" rock 5-1/2 sack mix with 20% fly ash and a 3" slump. The lower the slump the less water in the mix, and concrete is stronger with a low water cement ratio. Water the footing trench and sides to prevent the dry soil from sucking moisture from the fresh concrete.

You can see in the attached photos that the concrete coming out of the hose is quite stiff, but we used the vibrator to consolidate the mud uniformly across the bottom of the footing trench and around the reinforcing steel.

We made two passes around the perimeter; the first pass up to the bottom of the form boards; then thirty minutes later, after an initial set, we made the second pass to the top of the forms. The vibrator accomplished much of the leveling, then Khyber and Edward used wood floats to flatten the concrete exactly to the top edge. A crisp edge makes for a better seam with the rammed earth.

After a thorough site and tool clean-up, we wet down the concrete and saturated the footing/earth interface to slow down the curing process.

For this first footing we poured a total of 18 yards at a cost of $112 per yard. The 3" line pump with operator cost $580. From start to finish it took about 3 hours.

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