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How to Repair a Rotted Porch Post | Ask This Old House

Ask This Old House general contractor Tom Silva shows how to permanently patch a decaying porch post. (See below for a shopping list, tools, and steps.)

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Tom used a half-lap joint to attach the new post to the old post. He then used “Ready Patch” exterior spackle to fill the small gaps. It is manufactured by Rust-oleum [https://www.rustoleum.com/].

Shopping List for How to Repair a Rotted Porch Post:
– 2x4s [https://amzn.to/2Lwm9DJ], used as temporary support posts
– Two sawhorses [https://amzn.to/2LoRI3Q] – Rough-sawn cedar 6×6 [https://amzn.to/2MWKYfk], to patch rotted post
– 100-grit abrasive disks [https://amzn.to/2ZM0exz], for random-orbit sander
– Construction adhesive [https://amzn.to/2HPObsZ], for adhering the new post section
– 5-inch structural screws [https://amzn.to/2MWXo74], to secure the new post section
– Exterior-grade wood putty [https://amzn.to/2LjUoiW], for filling holes and cracks
– Spray primer [https://amzn.to/2LlENiP] and paint top coat [https://amzn.to/2MVpsb1]

Tools List for How to Repair a Rotted Porch Post:
– Cordless impact driver [https://amzn.to/2LraKFj] – Hydraulic jacks [https://amzn.to/2NQp1OM], to temporarily support the porch roof
– Reciprocating saw [https://amzn.to/2NQJfI5] – Circular saw [https://amzn.to/2zWYuY0] – Layout square [https://amzn.to/2UuozXK], for marking scarf joint cutlines
– Random-orbit sander [https://amzn.to/2ZQYjb8] – Hammer [https://amzn.to/2UuaXvL] and wood chisel [https://amzn.to/2PNvVqI], for cleaning up scarf joint
– Caulk gun [https://amzn.to/2UtWobu], for applying construction adhesive
– Putty knife [https://amzn.to/2NYqiDg], for spreading construction adhesive
– Power plane [https://amzn.to/2NQ9C0L], to plane down the new post section
– 3-inch sash paintbrush [https://amzn.to/2ZM27KR], for applying paint

Steps for How to Repair a Rotted Porch Post:
1. Unscrew and remove the handrail attached to the rotted porch post.
2. Temporarily support the porch roof on either side of the rotted post with a hydraulic jack and a long 2×4 post.
3. Use a reciprocating saw to cut the top of the post free from the overhead beam.
4. Remove the rotted post and lay it across two sawhorses.
5. Cut away the rotted section from the bottom end of the post using a circular saw.
6. Cut a new post section from a rough-sawn cedar 6×6.
7. Mark and cut a half-lap scarf joint into the new post section using a circular saw and reciprocating saw.
8. Set the new post section on top of the old post and trace the half-lap scarf joint onto the old post.
9. Cut a mating scarf joint into the old post.
10. Sand the joint smooth with a random-orbit sander, then fine-tune the joint with a hammer and chisel.
11. Apply several beads of construction adhesive to the scarf joint cut into the post.
12. Evenly spread the adhesive over the entire joint with a flexible-blade putty knife.
13. Fasten the new post to the old post with four 5-inch-long structural screws. Use an impact driver to drive the screwheads about 1/4 inch below the surface.
14. Use a power plane to trim the new post section flush with the old post.
15. Fill all screw holes and cracks with exterior-grade wood putty.
16. Once the putty dries, sand the post smooth.
17. Coat all bare wood surfaces with exterior-grade spray primer.
18. Screw the base plate to the bottom of the post.
19. Stand the repaired post back in place on the porch, then release the hydraulic jacks and remove the temporary 2×4 posts.
20. Secure the top and bottom of the post with screws, then apply a paint top coat to the post.
21. Reattach the handrail to the post.

About Ask This Old House TV:
Homeowners have a virtual truckload of questions for us on smaller projects, and we’re ready to answer. Ask This Old House solves the steady stream of home improvement problems faced by our viewers—and we make house calls! Ask This Old House features some familiar faces from This Old House, including Kevin O’Connor, general contractor Tom Silva, plumbing and heating expert Richard Trethewey, and landscape contractor Roger Cook.

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How to Repair a Rotted Porch Post | Ask This Old House


  1. What angle was used for that cut on the column and base?

  2. Please, what is best paint for exterior wood column? Thank you

  3. How was the bottom of the column attached to the deck? I did not see anything fixing it in place!

  4. how many degrees angle are the scarf cut done in? it appears to be 23 degrees,
    is there "an ideal" distance to keep between the 2 scarf cuts?

  5. “I can’t even tell where the patch is!” he said, as the camera zoomed in on the obvious patch joint.

  6. The bottom joint will collect water with that angle for sure.

  7. I could see the repair lines.

  8. Dowels work even better than screws Tom.

  9. question, how much is a job like this???

  10. Does anybody knows someone who does like this in St. Louis area? Thanks.

  11. This is tremendously helpful…my problem is the rotting posts I have are 25- foot-tall columns, so everything is about twice the size.

  12. Excellent video. My question is what direction the scarf cut should face when I replace the repaired porch post? I read from another online forum that "the plane of scarf should be perpendicular to the deck ledger or deck beam".

  13. How do you fix the bottom of the post to the verandah deck?

  14. Someone repairing that in 80 yrs is gonna be like what moron did this??

  15. I wish i had 1/1000 nth of this guys knowledge. I'd be set.

  16. So glad I found your video as I have the exact same issue with 2 of my verandah posts. I'm curious as to why you didn't prime the underneath of the base plate though.

  17. I am a carpenter over 30 yrs, yet i always learn something new when i watch this old house, thank's guy's.

  18. What angle are you using to cut the two parallels ???

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