Category Archives: 2. The Site, Excavation, and Foundation

Lower Level Slab – Tinted Concrete

The flatwork guy (Gough Concrete) poured the lower-level slab on Thursday and saw-cut the control joints on Friday. I stopped by on Saturday to take a look. We used a 2% mix of Solomon liquid color, which they call “smoke.” It’s just right. The tint is significantly darker than natural concrete, but still comes across as gray, not black. This color in this concentration costs $39 per cubic yard of concrete. Given that the mud itself only costs $110 per yard, that’s pretty significant. However, given that for this I get a finished floor, I consider the tinted concrete a bargain. This floor cost $5.40 per square foot for everything (#4 rebar, pump truck, concrete, tinting, placing the concrete, finishing the concrete, coating with an acrylic sealer, and saw cuts). This did not include the 15 mil vapor barrier and the under-slab insulation, which my plumbing and heating guy did.

The slab ended up being 6 inches thick instead of 5 inches (meaning the gravel was a bit low), which cost an extra $270 for another 2.5 yards of concrete. The control joints are basically on the same grid as the rooms, stairwell,  and passageways, although I split the larger rooms in half so that the joints are not more than about 10 feet apart. (Control joints are created by sawing a 3/4 inch deep groove in the concrete. This gives some visual definition to the space and encourages the concrete to crack on the lines instead of diagonally across the room. (That sort of works…but avoiding cracks altogether is a fool’s errand.)

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Footings are the roughly one-foot thick slabs of concrete on which the foundation walls of the house rest. They are designed to be large enough to distribute the weight of the house onto the excavated soil surface such that the soil does not collapse from the load. As a practical matter they tend to be 20-72 inches wide depending on what part of the house they support. They usually need to be 24-48 inches below the ground surface (depending on region) to be below the frost line.

Placing the footings is a pretty remarkable thing to watch. A crew of 8 (Stone Construction) arrived at 7am and they left around 6pm. With another two hours of work the next morning to strip the forms and pack up, I had completed footings.

This not a fussy construction task. They take a trailer full of lumber and hammer it together in the rough shape they’re after. They pump the forms full of concrete, and then trowel the top surface to a snapped line, which defines the top surface of the footing. The foundation walls are then built on top of these troweled surfaces. The photos tell the story.

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