Found out why my slab edges kept spalling after 5 years

I was reading through some old ACI stuff online and found out that if you finish the edges too early with a steel trowel before the concrete has set enough, it traps water right at the surface. That weakens the edges and they start chipping off after a few freeze-thaw cycles. I had been doing it that way for years thinking I was saving time. Has anyone else run into this issue with their driveway or patio jobs?

3 comments

3 Comments

joel_jones17d ago

Yeah @markh85 makes a good point about the mix being a BIG factor. I've seen guys use a super wet slump for easy finishing and then wonder why the edges flake off later, no matter when they troweled. But I think the real killer is finishing too early on top of a low air entrainment mix in a freeze thaw zone, that combo is a RECIPE for trouble. Even a decent mix can fail if you trap bleed water under that tight steel finish right at the edges.

the_jennifer17d ago

Read somewhere that water to cement ratio matters more than people admit.

markh8517d ago

Gotta disagree with you a little here (respectfully). I've finished edges early for years in my own driveway work and never had spalling issues - it's usually more about the mix being too wet or not enough air entrainment for your climate. Steel troweling can cause problems for sure, but I think it gets blamed for a lot of stuff that's really about the concrete quality itself.