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How to Replace a Porch Column Base

This Old House General contractor Tom Silva shows a homeowner how to remove and repair the rot eating away at his porch’s support post.

Tom Silva lends some support to a homeowner suffering under a rotted porch post. Tom and the homeowner dig into the rotten post base to find the issue and then get to work removing the affected wood. Next, Tom shows the homeowner how to mill new components from a recycled, water-resistant material before putting everything back together for caulk and paint.

How To Repair Rotted Porch Post Base

  1. Place the 4x4 post and bottle jack underneath a header on the porch and lift the porch roof slightly until the post is free from the ground. Remove any of the rotted material by hand, but do not reach under the post for safety’s sake.
  2. Use a reciprocating saw fitted with a 10-inch wood cutting blade to remove the rot. Be sure to make this cut as level and evenly as possible.
  3. Cut a piece of the rice hull board or wood to the correct square dimensions. Often, this is 2 or 3 inches wider than the post’s diameter. It might be necessary to double this block with an additional layer of wood to match the other posts. If that’s the case, glue the two blocks together with a fast-setting adhesive.
  4. Place the block under the post and level it side to side and front to back with shims. Once level, place small strips of wood along the perimeter on top of the block. Use the scribes to mark the pitch of the surface on these strips. Be sure to mark each strip and its location as you go. Cut the strips along the scribe lines on a bandsaw or table saw before gluing them to the block with the adhesive.
  5. Use the scribes to draw a circle of the appropriate size on a piece of the rice hull board or wood. For thicker profiles, screw two layers of the wood together before cutting along the circle with the jigsaw. Sand both layers smooth and evenly, and add detail with a router, if desired.
  6. Repeat the last step, but with a smaller circle to create a cascading profile. Drill a ¾-inch hole in the middle of each of these circles to allow for airflow and prevent future rot.
  7. Assemble the pieces under the post. Before lowering the post, squeeze a bead of construction adhesive between the post and the new base.
  8. Lower the jack slowly, allowing the post to settle on the base and squeeze the excess construction adhesive out. Smooth the excess adhesive before allowing it to dry.
  9. At each corner, drive a screw from the top-most layer of the base into the bottom base. Fill the screw holes and paint.

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