Limestone Soil and Gate Post Holes
Most people dig the post hole to the depth printed on the hardware sheet and stop, even when the bit has hit a ledge of rock at twenty inches. Around Georgetown, TX the ground changes between one lot and the next, and metal gates georgetown three word wednesday lays out the digging order for each kind of ground it finds. Limestone soil and clay need different tools and different footings under the same gate.
How deep does a gate post hole need to go?
A gate post hole should reach below the active zone of the soil, which in Williamson County means at least thirty inches for a light single swing and closer to forty-two for a heavy leaf or a gate with an operator. Depth is a third of the post height above ground as a working rule, and a longer post gets a deeper hole. A shallow footing rocks the post, and the frame then drags a latch or a corner.
What happens when the hole hits limestone?
A hole that hits solid limestone is either drilled deeper with a rock bit or widened to take a larger footing. Drilling into the rock and setting a dowel or the post itself into epoxy locks the post to the ledge, which is stronger than a deep concrete column in loose soil. A rock bar and a jackhammer attachment are the fallback when a drill rig will not fit through the side yard.
Why does clay move a gate post?
Clay swells with the Texas wet season and shrinks in a dry spell, and the movement pushes on the concrete from the sides. A post set in a straight column of concrete can be lifted by the swelling soil over several seasons. A bell-shaped footing, wider at the bottom, and a smooth sleeve around the upper section keep the clay from gripping the concrete.
How does water around the footing matter?
Water that stands at the base of a post speeds rust on steel and softens the soil under the concrete. The top of the footing is crowned so rain runs away from the post, and the ground around it is graded at least a few inches over ten feet. A gate near the San Gabriel River or in a low spot off Lake Georgetown needs gravel at the bottom of the hole for drainage.
How long does the concrete need before the gate hangs?
The footing needs at least three days before the frame is hung, and seven days before an operator is mounted and run. Concrete reaches walking strength within a day, but a gate leaf puts leverage on the post that a green footing cannot hold. A hinge loaded too early will shift a quarter inch, and that shows up as a latch that misses.