Installing Posts

Intro

Allow a day or two for the concrete to set and start to cure; it will take a week or so to achieve full strength.

A post level is an indispensable tool for installing posts. It tells you at once whether the post is plumb in both directions and leaves both hands free to work.

High-quality pressure-treated posts are fully saturated with a chemical that will keep them from rotting for decades. For extra protection, soak the cut ends in a bucket of sealer before installing them.

Use a level and a long board to estimate the height of each post. Set posts about a foot longer than you will need them; you will cut them to exact height later.

These steps show how to cut posts that will have beams placed on top of them.

Prestart Checklist

Time
About 30 minutes to install a post anchor, temporarily brace a post, measure and cut a post to height

Tools
Post level, hammer, drill, tape measure, circular saw, layout square, wrench

Skills
Driving screws, checking for level and plumb, cutting with a circular saw

Prep
Pour footings with J-bolts. Use string lines to mark the footings for posts that are correctly aligned.

Materials
Posts (usually 4x4s), adjustable post anchors, 1x4s or 1x2s for braces and stakes, 2-inch screws

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Step 1

Install a post anchor on a footing and finger-tighten the hold-down nut so that the anchor is fairly stable but movable. Insert a post, fasten it to the anchor with one screw, and attach a post level. Stake and brace the post -- position the post so it is plumb, and screw the braces to the post.

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Step 2

Use a level to mark the first post for the height of the decking. Make sure that the decking will be at least 1 inch below the threshold of the doorway.

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Step 3

Measure down from the top of the decking. Strike marks to indicate the thickness of the decking, the width of the joists, and the width of the beam. Cut the post at this height with a reciprocating saw.

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Step 4

You can use a line level or a water level to mark all of the posts for cutting level to the first post. Over short spacing, you can use a straight board and a carpenter's level, as shown. Set one end of the board on the first post. If you are holding the board against more than one post, it might help to have someone hold the other end of the board. Mark all the posts and double-check that the marks are all level with each other; then cut the posts.

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What If... You have to add a bolt after the concrete has set?

If a J-bolt is seriously misaligned, cut it off and buy threaded rods and epoxy made for retrofitting concrete anchors. Drill a hole in the footing using a masonry bit slightly larger in diameter than the rod. Vacuum out all the dust. Inject epoxy into the hole and insert the threaded rod. The epoxy will set firm in about a day.

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Refresher Course: Options for setting posts

Some deck designs call for posts that are set in holes filled with concrete or tamped dirt. The concrete method is challenging because all the posts must be perfectly aligned when the concrete is poured.

A 42-inch-deep hole is typical for both methods. Tamp the bottom of the hole and throw in a few inches of gravel. Tamp the gravel. Insert the post.

If you will be filling around the post with concrete, drive several 16d nails into the post to help anchor it in the concrete. Brace the post plumb in both directions.

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