More than a few of my jobs have been for clients who contacted me after reading one of my JLC articles. That was the case for this project, which involved replacing four structural support columns in the basement of a three-story house built in 1895. My client, who had just purchased the house, was concerned about cracks in the basement’s concrete slab floor that were radiating out from each column, as well as about some dips in the flooring at the first-floor level and a few binding pocket doors. The scope of work included additional columns as needed to address these issues.
Other contractors had looked at the job but declined to take it on; I’d done similar work before (see “Shoring a Sagging Floor,” Mar/12), so I knew what to expect. Still, this was one of my most challenging basement projects, with a concrete floor consisting of two slabs poured at separate times, one on top of the other, over a subbase of broken-up ledge. The bases of the four steel columns were bearing on the stone substrate and buried beneath the two slabs, so the concrete needed to be broken up just to remove the embedded columns.
I started by assembling cribbing from 8-foot-long 4x4 pressure-treated posts cut into 2-foot sections. Solid support is needed for the 20-ton screw jacks that I use to lift floor framing enough to remove a support post (1), and because basement slab floors are rarely level or smooth, I always shim the assembled cribbing carefully (2). Then, while jacking up the temporary 4x4 supports, I check them frequently for plumb in both directions (3). The cribbing at each location would be in place for about a week, during which time a lot of weight would bear on the assembly. With plumbing, waste lines, and gas supplies at stake, a major shift in the position of the building could be catastrophic, so I worked slowly and carefully to make sure everything was solid, flat, level, and plumb as I proceeded.
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