Page 67 - Masonry and Concrete

Concrete Construction Techniques
66 CHAPTER THREE

FIGURE 3-24
Strike-off board.

previously marked on top of the form boards (Figure 3-28). Lay a 2
12 across the tops of the forms to kneel on while you work, and use the
edge as a guide to assure that the joints are straight. If you want to saw
rather than tool your control joints, wait until the concrete has hard-
ened for about three hours. Use a circular saw with a masonry cutting
blade, and saw grooves to a depth of about one-fourth the slab thick-
ness (Figure 3-29). Use a straight piece of 2 4 as a guide.
After forming the control joints, use a float to smooth the concrete
surface and bring a sand and water mixture to the top of the slab. Hand
floats are made of wood, plastic, or composition materials. Magnesium
floats are light and strong and slide easily over the surface. Magnesium
floats are recommended for air-entrained concrete. Wood floats drag on
the surface and thus require greater effort, but they produce a surface
with relatively good skid resistance. Hold the float nearly flat and move
it in wide sweeping motions (Figure 3-30), smoothing over any marks or
gouges left from edging or jointing. If water comes to the surface when
you begin the floating, stop and wait awhile before trying again. After
floating the surface, go back over the edges and control joints with the

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