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A footing that will heave
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Here's how to get a solid, frost-proof footing. When you pour concrete footings, hold the cardboard concrete form tube about 12 in. up from the bottom of the footing. Do this by nailing the sides of the tube to the center of a tic-tac-toe grid of 2x4s at the top of the hole. Then dump concrete through the tube into the bottom of the hole. After the wide part at the bottom of the hole has filled, the tube will fill too. Flare the sides on concrete footings so the footings will resist heave in harsh winters when frost penetrates especially deep. Greater width at the bottom will also distribute weight over a larger area. Mound soil around the posts after the backfill settles to direct runoff water away from the post.
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