I've been using the wrong concrete mix for interior slabs for years

A guy on a job in Phoenix last month saw me ordering 4000 psi mix for a warehouse floor and asked if I was worried about shrinkage cracks. He said for big interior pours with no freeze-thaw, a lower psi mix with a good water reducer actually performs better and costs less. Has anyone else switched to a 3000 psi mix for similar jobs and seen fewer issues?

3 comments

3 Comments

hugobarnes3mo ago

Worried about shrinkage cracks" is putting it mildly. I spent a decade chasing those hairline cracks before a batch plant guy set me straight on the lower psi mix. It was a real forehead-slapper moment for sure.

king.aaron3mo ago

Forehead-slapper moment" is right. I guess we all pay for that one expensive class on proper concrete.

anthonyhunt1mo ago

Did you ever try the wet burlap method for the first week? I learned that one the hard way after a patio job turned into a spider web of cracks. Keeping it damp and covered for at least 7 days made a huge difference for me, even with the lower psi mix. Also throwing in some control joints early saves a ton of headache later. Just my two cents from screwing up plenty of times myself.