Hot take: I used to think all concrete was the same. Then I poured a sidewalk in July vs November and wow.

Back in 2021 I poured a driveway in July during a heatwave in Phoenix. It set so fast I barely got it finished before it hardened wrong. Then last month I did a small sidewalk in Denver when it was 40 degrees out. Had to use warm water and blankets to keep it from freezing. Same bag of mix but totally different results. Ever had a pour go sideways because of the weather?

3 comments

3 Comments

elliotm7012h ago

Man, that's the truth and then some. @johnson.paul nailed it about flash set in heat - I learned that one the hard way back in 2019. I was helping a buddy do a patio slab in late August in Texas and we didn't have any retarder on hand. The concrete started going off while we were still trying to screed it. Ended up having to break it all up and start over with ice in the water. Now I always check the forecast and keep a bag of retarder in my truck year round. Cold weather pours are almost worse though, got a story about trying to cure a slab under tarps in a snowstorm once and the blankets froze to the concrete overnight. Temperature just messes with everything.

johnson.paul13h ago

And that temperature swing really changes how you work the concrete because the chemical reaction speeds up or slows down way more than people realize. Hot weather forces you to add retarder and keep the mix cooler or you're fighting a losing battle against flash set. Cold weather you're doing the opposite slow curing but if it freezes before it gains strength then the whole slab is toast.

graydavis9h ago

HOLY COW that Texas story gives me flashbacks. I was working a job in Phoenix where the concrete mixer showed up late and the sun was already cooking the slab. We had to add ice AND use a misting fan just to keep the pour workable. But the craziest part was the next morning when I checked the edge and it had already started cracking just from the heat differential under the curing blankets. Weather is a beast and it doesn't care about your schedule.