The Brew Cabin

We just had our concrete driveway replaced (416 sq. ft in total) with new concrete (on Monday August 11th - a scorcher of a day). The concrete guy said that concrete needs 28 days to cure completely, and the best curing conditions is 100% humidity (which he says "that's under water"!!!). He says that I need to keep the pad wet for 28 days. I've been watering it down at least five times a day since Monday.

1) Is this really necessary?

2) Is this possible to keep it wet for 28 days??

3) In the August heat wave we have right now, the temperatures are reaching 35-36 degrees Celsius (hot for Saskatchewan, Canada), it is hard to keep up - the concrete's surface dries up so fast. It seems like a big waste of precious water (yikes - our water bill!)!!!

4) any other comments / advice?

Cory
Regina, Saskatchewan, Canada

Hi again Cory,

1 - theoretically: yes. Practically: no.

Although concrete does indeed reach its design strength at (or around) 28 days, it continues to harden long after that, and actually reaches something like 90% of design strength after 5 days. Maintaining a humid curing environment is really not essential for the full 28 days.

2 - Yes, if you set up sprayers or you live in a soggy climate like that or Ireland and Britain, but the usual practice is to use a membrane that's spray-applied to the surface to retain the water content of the concrete during the initial curing, and then peeled off after a few days.

3 - You could cover the slab with a membrane yourself. A polythene sheet will do, or even old sacking that is dampened down every 4 hours or so. It's too late now for a sprayed membrane, and I guess, 3 days after the pour, a great deal of the initial cure is complete, especially with such high temperatures, so there's very little to be gained by using any membrane this late in the process.

4 - Spray the concrete enought to dampen the surface and cover it with polythene for another 3 days - after that, it should be fine. You might find some minor, surface 'hairline' cracks, but these aren't worth losing sleep over, and occur in virtually all concrete. If the preparation was right before the pour, then there's not alot to be gained by spraying, sheeting or submerging it for the next month!

HTH