How to Repair a Rotten Wooden Porch Post

Most of the wooden porch posts rot out at their bottom portion. The best and cheapest solution is to cut out the lower rotten part of the post at joining point of  its square base with turned or shaped  center portion and transplant a wooden base made from a stable wood species like fir to replace it. You can do the repair at the same place. It may be essential to take out the railings, install a temporary support for porch post and make certain that top of the post is firmly fixed the beam.

Tools and Materials Needed:

  • Fir wood block
  • 2 by 4 block
  • Light duty jack
  • Tape measure
  • Tri-square
  • Straight-edge
  • Power hand drill
  • Drill bit
  • Wood screws
  • Belt sander
  • Reciprocating saw
  • Wood saw
  • Router
  • Rounding bit
  • Arbitron epoxy adhesive
  • Sand paper
  • Disposable putty knife
  • Primer
  • Paint
  • Painting brush

Step 1 - Supporting the Porch

Position a 2 by 4 block and fix a light-duty jack under the porch beam. Apply just sufficient pressure so that it can carry the load when the replacement post is reconstructed and installed

Step 2 - Estimating the Size of Replacement Piece

Evaluate the length of the damaged portion by drilling a series of explorative holes into the bottom portion of the rotten post with a 1/4-in. drill bit. You will have to substitute the bottom part of the post. Normally the portion below the turned center part is completely replaced

Step 3 - Removing the Rails

Cut the nails of bottom railing of the porch if they bother you to work freely. However, it is best, if these can be left in place.

Step 4 - Cutting off the Part to be Replaced

Mark the cut-off lines on all sides of the post with a tri-square. Take the dimensions of the replacement piece to be made. Cut away the rotten part with a saw. It is better to leave the marked lines. Face the end of the post using a belt sander up to marked lines and make sure that the face is flat and level. Check using the tri-square.

Step 5 - Making the Replacement Block

Cut the replacement block to size and finish its surfaces with the sander. Ensure that the dimension match up perfectly with that of existing post. The mating face should be flat and level to match bottom of cut post. The lower bevel on the face meeting the floor also should be perfect.

Step 6 - Apply Adhesive for Fixing

Before you fix the replacement block, coat the end grain on the top of the block and at the bottom of the post with epoxy wood adhesive system like Arbitron or System Three. Prepare the adhesive by mixing the epoxy agent with the hardener.

Step 7 - Fix the Block

Slip in the replacement block under the post. Ensure that all sides are aligned properly. Use a tri-square or a straight-edge to for checking. Move down the old post on to new block so as to press over it. Clamp together the 2 components by fixing four 3 inch long deck screws at angle through the top post into the new block from all sides. The screws holes can be pre-drilled with a countersinking bit to avoid the splitting of the wood. Remove the adhesive squeezing out at the joint with a disposable putty knife.

Step 8 - Blending the Joint Line

Blend the joint line by rounding at edges on the joint line between replaced block and the post with a rounding bit mounted on a router. This will hide the joint and the joint will appear like a decorative bead to a casual observer.

Step 9 - Finishing

Sand the replaced part with medium and fine sand paper. Coat it with primer. When the primer dries up, paint it for its longevity.