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Hot take: a pour in Flagstaff last summer made me rethink wetting down subgrade before a slab
Half the crew swears pre-wetting the subgrade saves you from a dry mix sucking the water out, but after watching a 40x60 slab in Flagstaff cure out with plastic shrinkage cracks all over the north edge, I'm wondering if we were just hiding a bad mix design the whole time.
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the_emery18d ago
Man that Flagstaff job sounds rough, 40x60 is way too much concrete to watch crack up like that. Been there with a shop slab in Tucson where the north side looked like a road map after we thought we did everything right. Pre-wetting can help with the dry mix pulling water out, sure, but it also cools the ground down and that temp swing between wet subgrade and hot pour can bite you on the edges. Sounds like the mix might've been short on water or low on cement and the wet down just masked it till cure. Sorry you had to eat that one, it's the kind of thing that keeps you up at night.
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