How to Mount Fence Posts on Concrete

Written by mark morris
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How to Mount Fence Posts on Concrete
Use a socket wrench when tightening lag bolts to hold your posts upright. (socket wrench image by Jim Mills from

Mounting fence posts on concrete can be problematic. Cutting through the concrete to sink posts into the soil frequently causes cracks in the concrete and can be cost-prohibitive. Surface mounting is possible with the correct brackets and mounting hardware. Since you will be boring holes in concrete, be sure you have marked the correct positions for your posts before mounting; holes in concrete can be filled, but cannot be undone.

Skill level:

Things you need

  • Tape measure
  • Pencil
  • Chalk line
  • Post brackets
  • Square
  • Drill
  • 3/16-inch rotary mason's bit
  • Masking tape
  • Compressor
  • Concrete screws
  • 1/8-inch wood bit
  • Lag bolts
  • Socket wrench

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  1. 1

    Measure from the edge of the concrete to pinpoint the post line placement, using a tape measure. Mark the centres of the first and last post on the concrete with a pencil. Snap a chalk line between these two points down the centre of your post line.

  2. 2

    Measure from one of your end post marks and use chalk to mark the concrete for a post every 8 feet.

  3. 3

    Set a 4-by-4 galvanised post end bracket centred on each mark. Use a square to line them up straight with the centre line and mark the screw holes in each bracket onto the concrete.

  4. 4

    Bore a 2-inch-deep hole at every mark, using a rotary mason's bit, 3/16 inch in diameter. Wrap masking tape around the bit, 2 inches from the tip, to mark the proper depth. Use a compressor and air nozzle to blow the concrete dust from the holes.

  5. 5

    Position a bracket lined up with each set of pilot holes. Drive one 1 3/4-by-1/4-inch concrete screw into each hole. Drive the screws in until they pull the brackets firmly against the concrete. Do not overtighten. Use every hole.

  6. 6

    Stand a 4-by-4-inch treated lumber post, cut to the height of your fence, in a post bracket. Use a level and have a helper hold the post upright and plumb. Mark the screw holes in the bracket onto the face of the post. Mark every hole.

  7. 7

    Drill 1/8-inch pilot holes 2 inches deep on every mark. Repeat this marking and boring process for each post.

  8. 8

    Return the post to the bracket and use a socket wrench to drive a 3/16-by-1 1/2-inch lag bolt into every pilot hole to hold the post firmly upright. Repeat this attachment process with every post in the line.

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