replacing rotted front porch posts
I have an 85-year old house with a lovely front porch. It has brick columns to half the height, topped by a concrete cap with a wooden base (2" thick block of wood) embedded in it (!), followed by wooden posts up to the wooden beam along the roof line. The wooden posts and the beam are "box beams", assembled from old, dense red pine that's about 7/8" thick. The wooden posts are just under 5' tall.
I've just discovered that the wooden blocks in the concrete at the bases of the two corner posts are quite rotten. There's very little settling to speak of - looks like they did their job nicely for 80 years or so, despite being sunk into a concrete well!
Jacking and supporting the roof adequately aside (fine with that), I've got a couple of questions about materials...
I'm planning to replace the bases, and am trying to choose between replacing them with wood, or with concrete formed to match the shape of the original wood. A wood replacement would have to be with some dense weather-resistant species, like some nice older mahogany that I have (quite a "waxy" variety), or perhaps white ash, then well treated with wood preservative, sealed properly in place, and painted thorougly and well. Concrete on the other hand could be made to look very similar to the original, however putting a modern mix into a well of 85-year old mix...differing expansion and contraction characteristics...?
I'm also planning on installing a "structural" post at each corner, and adding the box on the outside as purely a cosmetic element. A small gap would be left for ventilation at the bottom. My two choices for the structural post would be a steel jack post with suitably-sized plates top and bottom, or a wooden post (likely 6"x6" PT) fastened to a galvanized spacer fitting (simpson strong-tie) at the bottom to keep it dry, plus one at the top to keep it in place.
So: wood or concrete? wood or steel?
Concrete and steel.
Pour the concrete with a thin expansion joint. Seal the top with a good quality exterior sealing caulk. Silicone probably would not seal as tight or last as long as a rubber type sealer. A good product for this application would be Conklin 360 or a Dap exterior siding sealer. If you are considering a structural post, you should look in to a steel post with a mounting flange at the top. These can be made at a shop for less $$ than a jack-post. Fill it with concrete, let it set, prop it up in the concrete form and pour the concrete right around it. Solid as anything you can do. Use lag screws to attach the top to the beam.
Oh!, the expansion joint can be made of thin fan-fold siding insulation and will allow a minimum of movement.
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