How to Install a Post on Top of Old Concrete

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Concrete fasteners secure objects to concrete.
Concrete fasteners secure objects to concrete. (Image: Hemera Technologies/AbleStock.com/Getty Images)

Many home improvement projects require that you anchor something to an existing concrete floor or slab, such as installing light posts, mailboxes or even pergolas. This can seem challenging since posts are typically buried in the ground. Attaching posts to an old concrete surface requires that you inspect it for structural integrity and then attach special brackets. You secure the brackets to the concrete with fasteners designed to penetrate and grip the hard material.

Things You'll Need

  • Post bracket
  • Safety glasses
  • Earplugs
  • Hammer drill
  • Masonry bit
  • Tape measure
  • Masking tape
  • Shop vac
  • Stainless-steel concrete sleeve anchors
  • Wrench

Walk along the old concrete surface and inspect it for visible cracks or crumbling material that may indicate a structural failure. If any of these are present, choose another installation location for the post or replace the concrete prior to installation. Weak concrete may fail when you drill into it or add the extra weight of a post.

Place a post bracket on the bottom of the post to ensure it fits snugly. Brackets are available in multiple sizes to fit the diameter of various posts.

Remove the bracket from the post and place it on top of the concrete surface in the desired location. Insert a pencil through the lower screw holes to mark them on the concrete.

Set the bracket aside and put on safety glasses and earplugs. Insert a 1/4-inch-diameter masonry drill bit into a hammer drill. Measure up from the bottom of the bit until you reach 2-1/4 inches. Wrap a piece of masking tape around the bit.

Place the tip of the bit on one of the screw holes and squeeze the trigger to drill out the hole until the bottom of the tape reaches the top of the concrete. Repeat the process for each remaining hole.

Plug in a shop vac and suck out all of the concrete dust from inside the holes.

Insert the post bracket back onto the bottom of the post and secure it to the post with the provided screws and a power drill. The post bracket has a lip that sits on the post and has holes for the screws.

Raise the post vertically and align the lower bracket holes with the holes in the concrete. Ask an assistant to hold the post upright and steady.

Insert a 1/2-inch-diameter stainless-steel concrete sleeve anchor into each screw hole in the bracket. Place a wrench around the nut at the top of each anchor and turn it clockwise two to four times until it is tight.

Tips & Warnings

  • Some posts come with a flat plate mount already attached. If this is the case, an additional post mounting bracket is not required.

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