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Tips for Crack-Free Concrete Slabs - Continued A well-organized, well-timed, uninterrupted work flow is essential. Hand-trowelling the perimeter along walls and around obstacles as concrete is being placed is a good way to start (Figure 8).

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Figure 8. To keep the job moving, it's a good idea to hand-float the slab perimeter as the concrete is placed.

Have the power trowel fueled up and ready to go before you need it. If you exercise a little patience before power trowelling is begun, you can avoid displacing the softer concrete and causing potential low spots in the finished slab (Figure 9).

Figure 9. All bleed water should have left the surface before any hand-finishing or power-trowelling begins (top). Even with a power trowel on the job, some hand-finishing is necessary around obstructions (above).

Curing

Don't forget to take care during the curing stage. Initially, the temperature will rise quickly, peak, and then start to drop. This process is stressful on a new slab and can cause failures. Wet curing keeps the slab from drying out too fast during this process. Cover a fresh slab with a layer of burlap immediately after finishing, and keep it wet with a lawn sprinkler for at least three days (ideally seven days). Or, cover the slab with a layer of plastic. Wet curing will ensure an even and controlled cure. In cold weather, make sure that fresh concrete is protected from freezing (Figure 10).

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Figure 10. If there is any chance of freezing, blankets are used to protect the subgrade before placing the slab (top), and to cover the fresh concrete for at least three days after (above). Gabe Martel is a project manager and construction superintendent in Pembroke, Ont., Canada, with over 35 years of experience.