Installing Mortised Posts and Rails

Increase your home security and add a beautiful mortised fence to your landscape

Installing Mortised Posts and Rails

If you want a fence that looks cleaner and neater than most kinds with rails mounted between or on the fronts or sides of the posts, consider a fence with mortised posts and rails. "Mortised" simply means that line and end posts have mortises, or holes for insertion of rail ends, cut into them.
Shown at left: (A) line post; (B) rail; (C) corner post.

The mortised post-and-rail fence has fewer components than most fences, which makes it easier to install. Line posts usually have mortises at 10 and 24 inches from the top. Corner posts have mortises at the same height, but are mortised so the rails meet at 90 degrees. The rails are identical and tapered to fit in the mortises. This guide will teach you how to install a mortised fence.

Planning your fence
Planning your fence  - Mortised Posts Rails

• The parts on a mortised post-and-rail fence are prefabricated, and because of the rail lengths, the posts are usually spaced 6 feet apart and no taller than 5 feet. Both round and square posts are available; round posts tend to give the fence a more rustic feel.
• The rails have tapered ends that fit into mortises in the posts. The mortise runs completely through the post: One rail comes in from one side, the other from the other side. Corner posts are mortised on adjacent sides. Mortises for corners aren’t as deep as they are for line posts, so you may have to shorten a rail in order to fit it snugly in the post.
• Start a post-and-rail fence by digging holes for all the posts. Put a corner or end post in its hole, plumb it, brace it, and fill the hole with soil. Put the neighboring post in its hole and run the rails from mortise to mortise. Plumb and brace the post, and backfill the hole. Work your way along the fence, installing rails and posts one section at a time.

Lay out the posts
Lay out posts - Mortised Posts Rails

Lay out the fence with batterboards or stakes and string. Assemble the posts and fence rails on the ground along the string. Put a piece of tape on the string to mark the center of each post.

Dig the post holes
Dig post holes  - Mortised Posts Rails

Dig postholes below each piece of tape using a posthole digger. Make sure you dig deep enough so the post is at least 6 inches below the frost line or so one-third of the overall length of the post is buried (whichever is deeper).

Tip: If you’re fencing in horses, build a fence with a top rail that is at least 5 feet above the ground. Make sure you buy posts with mortises for a third rail to keep curious colts from squeezing through.

Put in a corner or end post
Put corner end post - Mortised Posts Rails

Coat the bottom of a corner or end post with roofing cement and plumb and brace it in its hole with scrap 1×4s or 2×4s. Verify that the post is plumb and screw the braces into place.

Fill the hole with concrete
Fill hole with concrete - Mortised Posts Rails

Mix fast-setting concrete in a wheelbarrow and pour it in the hole. Work a board up and down in the concrete to remove trapped air bubbles. Slope the top of the concrete with a trowel to direct water away from the post.

Put in line post
Put line post - Mortised Posts Rails

Coat the bottom of a line post with roofing cement and place it in its hole. Put one end of a rail in the end or corner post, then put the other end in the line post, wiggling as needed to get it to fit. Repeat with the second rail. Plumb the line post and check the rails for level. Fill the hole with concrete as before. If the concrete won’t hold the post in place, brace it as before.

Put in more line posts
Put more line posts - Mortised Posts Rails

Begin rolling over the still-wet cut-in strip. Keeping a wet edge prevents overlap marks in the finished ceiling. Load the roller regularly and roll slowly. Back-roll to blend the paint.