Question 1

How do I know if it's safe to pour concrete today?

Accepted Answer

Four numbers decide it: air temperature, relative humidity, wind speed about 18 inches above the slab, and concrete temperature. Run them through the ACI 305R evaporation formula — anything over 0.15 lb/ft²/hr means you are flirting with plastic shrinkage cracking. PourDay does the math live using weather data for your exact job site and gives a GO, CAUTION, or WARNING.

Question 2

When should you NOT pour concrete?

Accepted Answer

Three situations to walk away from: (1) Air temperature below 40°F and falling — hydration stops and the slab will not gain strength. (2) Air temperature above 90°F with low humidity and wind — evaporation runs away and the surface skins over before finishing. (3) Heavy rain in the forecast within 4-8 hours of placement, which washes out finish and air content.

Question 3

How long does concrete take to cure?

Accepted Answer

Initial set is 4-8 hours. Concrete reaches roughly 65-75% of design strength at 7 days, and 100% of design strength at 28 days — the standard benchmark for cylinder breaks. Hydration continues for months but 28 days is the structural number. These figures assume adequate moisture during curing; high evaporation during placement can permanently compromise strength.

Question 4

Why does concrete crack?

Accepted Answer

Most premature cracking traces back to pour day: high evaporation rate causing plastic shrinkage cracking, excessive heat accelerating the set, or restraint cracks from improper jointing. The first two are the ones contractors can prevent by reading weather correctly before placement.

Question 5

What temperature is too hot to pour concrete?

Accepted Answer

There is no single temperature — it is the combination of air temp, humidity, wind, and concrete temperature. 95°F with 60% humidity and calm wind can be fine. 85°F with 20% humidity and 15 mph wind is dangerous. ACI 305R uses the evaporation rate calculation to give the real answer.

Question 6

What is a safe evaporation rate for concrete?

Accepted Answer

ACI 305R recommends precautions when evaporation rate exceeds 0.15 lb/ft²/hr. Above this threshold, surface moisture evaporates faster than bleed water can replace it, causing plastic shrinkage cracking — especially with blended cements like Type 1L which have less bleed water.

Question 7

Is PourDay free?

Accepted Answer

Yes, PourDay is completely free for contractors. No subscription, no paywall, no premium tier.

Question 8

Can I track multiple job sites?

Accepted Answer

Yes, PourDay supports up to 10 saved locations. Each location gets its own real-time evaporation rate, 16-day forecast, and pour condition scoring.

Concrete pour conditions by city