Warning: Young guys are forgetting to wet the subgrade before pouring

Was on a site last week in Nashville helping a crew pour a driveway and the foreman just poured right onto bone dry dirt. I had to stop em and show them how the water was just vanishing into the ground before they even screeded it. I've been finishing concrete for 17 years now and I swear every new guy I see skips this step because theyre in too much of a rush. The old timers back in the 90s would soak the hell out of the subgrade the night before so the slab would cure even and not crack from the base pulling moisture out. If you dont wet it you get weak spots near the bottom and a bunch of surface checking later on. Aint nobody got time to rip out a driveway 6 months later because you didnt want to spend 10 minutes with a hose. Has anyone else noticed this getting worse or is it just the crews around me?

3 comments

3 Comments

lopez.simon24d ago

Man, you're dead on. I see it on every job lately too.

umathompson24d ago

You ever had to watch a fresh pour start turning white before they even get the float on it? That dry subgrade is like a vacuum for moisture and it will ruin your slab from the bottom up. I always wet it down good at least an hour before the truck shows up, and if it's hot out I'll do it the night before too. The new guys think they're saving time but they're really just setting themselves up for a call back in six months. A little water now saves a whole lot of headache later.

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casey_harris24d ago

Yeah but I gotta push back a little on doing it the night before. If you soak it that early and the ground is super dry or sandy, the water just drains away and you're back to square one by morning. I've seen guys drench it at 9pm and by 6am the subgrade is bone dry again, especially in summer. The trick is timing it so the water is still sitting on the surface when the mud hits, not evaporating or soaking in hours earlier. I usually hit it about 45 minutes before the truck, heavy enough that it puddles but not so much that you're making mud. If the ground is really thirsty I'll do a light pass the afternoon before to pre-wet the deep stuff, then another good soak right before pour. Overdoing it the night before just wastes water and gives you a false sense of security.