3 out of 5ModerateRequires mid-level carpentry skills
$50 to $100
2 to 4 hours
In this video, Ask This Old House general contractor Tom Silva shows how to permanently patch a decaying porch post.
Steps for repairing a porch post:
- Unscrew and remove the handrail attached to the rotted porch post.
- Temporarily support the porch roof on either side of the rotted post with a hydraulic jack and a long 2×4 post.
- Use a reciprocating saw to cut the top of the post free from the overhead beam.
- Remove the rotted post and lay it across two sawhorses.
- Cut away the rotted section from the bottom end of the post using a circular saw.
- Cut a new post section from a rough-sawn cedar 6×6.
- Mark and cut a half-lap scarf joint into the new post section using a circular saw and reciprocating saw.
- Set the new post section on top of the old post and trace the half-lap scarf joint onto the old post.
- Cut a mating scarf joint into the old post.
- Sand the joint smooth with a random-orbit sander, then fine-tune the joint with a hammer and chisel.
- Apply several beads of construction adhesive to the scarf joint cut into the post.
- Evenly spread the adhesive over the entire joint with a flexible-blade putty knife.
- Fasten the new post to the old post with four 5-inch-long structural screws. Use an impact driver to drive the screwheads about ¼ inch below the surface.
- Use a power plane to trim the new post section flush with the old post.
- Fill all screw holes and cracks with exterior-grade wood putty.
- Once the putty dries, sand the post smooth.
- Coat all bare wood surfaces with exterior-grade spray primer.
- Screw the base plate to the bottom of the post.
- Stand the repaired post back in place on the porch, then release the hydraulic jacks and remove the temporary 2×4 posts.
- Secure the top and bottom of the post with screws, then apply a paint top coat to the post.
- Reattach the handrail to the post.