Postholing

Colin checks level on a porch post, embedded 42 inches deep in a posthole.

Colin checks level on a porch post, embedded 42 inches deep in a posthole.

Time to build the porch! We were waiting for Pillsbury, our excavation contractor, who finally returned yesterday to do some essential sitework. In particular, Todd and Tim graded around the house and the future breezeway where the porch will go. To give them access, we had to switch our temporary shed roof supports, bracing diagonally from the house exterior wall instead of vertically from the ground. Todd also let us borrow his trailer to pick up a hefty order of 6×6 lumber and bags of Quikrete – essential supplies for the porch foundation.

We installed ledgers to support the porch before Pillsbury Excavation arrived.

We installed ledgers to support the porch before Pillsbury Excavation arrived.

To start, the excavators augered a series of holes for the porch’s supporting posts, at locations Terry laid out. Then we measured the depth of each posthole and used hand tools to dig out any clay that caved in, for a uniform depth of at least 42 inches. Our chief implement for this job was the posthole digger, possibly the most aptly named tool on site. It’s basically a pair of shovels facing each other, connected with a pivot. You reach way down into your posthole, spread the handles to make the shovels chomp down on a clump of dirt, then lift the assembly up and out. We removed a whole lot of dirt this way to guarantee a proper embedment depth for the posts.

Digging a posthole with a posthole digger.

Digging a posthole with a posthole digger.

After checking the location of each hole, in went the 6×6 posts. Next came the tedious business of getting the posts square and plumb. When possible we braced the post with a 2×4 screwed into the ledgers Terry and Colin installed along the base of the house. That took care of alignment in one direction. We got the top of each post in exactly the right spot, held up a level, and pried from the bottom until the post was perfectly vertical. Then we rechecked the post’s location… because our next feat would make it a whole lot harder to move.

Into the hole goes an 80-pound bag of Quikrete.

Into the hole goes an 80-pound bag of Quikrete.

The postholes were much larger than the posts themselves, enabling us to anchor the posts with Quikrete and then backfill around them. We compacted the fill frequently by tamping it down with Sluggo or a smaller stick. Here I encountered a technique that I’ve never seen before, and that’s certain to send shivers down the spine of a commercial engineer. Instead of adding water to the Quikrete, we simply poured the dry mix under and around each post. As the logic goes, this powdery mix will eventually react with groundwater and harden into concrete all on its own.

I’m skeptical. How do you know when the concrete reaches full strength? Won’t the outer edges set first and prevent water from ever mixing with the inside? But here’s the big picture: each post ALREADY has a solid connection with the ground, buried in 42 inches of compacted soil. Adding any concrete at all is overkill, so when it comes to structural integrity I don’t worry.

Backfilling the posthole.

Backfilling a posthole.

Todd and Tim did additional sitework in the meantime, namely trucking in lots of gravel and re-grading the driveway for drainage. The level of this gravel finally matches the Barn slab, enabling vehicles to easily drive into the garage for the first time. I think Terry’s going to take advantage of the shelter this weekend to repair his truck!

The latest & greatest. All the posts are installed and the driveway is properly graded.

The latest & greatest. All the posts are installed and the driveway is properly graded.

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