Why More Concrete Doesn’t Mean a Stronger Footing

A common assumption is that more concrete around a post automatically means a stronger footing. It doesn’t — a post in the ground is only as solid as the ground around it, and concrete itself introduces problems that pure soil doesn’t.

Concrete holds moisture, and rot needs air, moisture, and a food source (the sugars naturally present in wood) to take hold. The worst possible place for a concrete-to-wood intersection is right at ground level, which is exactly where a typical footing puts it.

There’s a second, more structural problem: when you dig a post hole, the top of the hole is almost always wider than the base. As frost sets in seasonally, that shape lets frost heave actually lift the post — and your fence or deck post with it — right out of the ground, while dirt washes in underneath and raises the footing a little more every year. Belling out the hole doesn’t solve this either; if both the top and bottom of the hole are wider than the middle, frost will simply shear the concrete between the two sections.

The fix: keep concrete confined to the bottom half of the hole so frost anchors the footing in place rather than working against it, and use fine gravel or stone dust to set the post above the concrete footing — it acts as a lubricating layer that helps prevent frost from gripping and heaving the post.