I’m building a house, and the contractor will pour a concrete slab just before he leaves for the weekend.
I will hose down the slab with water for the next couple days till the concrete cures.
It’s summertime–temperatures are in the 90’s (35 C).
I dont live at the construction site–but I can be there a couple times a day. How often should I spray water over the slab?
How much water do I need to use?–is it enough to keep the surface slightly wet, or do I need to keep a deeper “pool” of water covering the slab? (it’s 1200 sq. feet–120 sq meters)
The contractor’s forms are built to the exact level of the concrete surface, no higher. Should I tell him to add an extra inch or so, to make it possible to flood the surface of the slab and leave it covered with enough water that won’t evaporate quickly in the heat?
Cover with damp burlap or straw. I’ve never seen a pool of water on a slab, but the only large slabs I’ve poured were after the first floor of the house was built.
I’m surprised the forms are exactly level all the way around. I’d expect the concrete to be leveled to a chalk line below the lowest section of form. I’m also surprised the concrete guy doesn’t have specific instructions for you.
burlap or straw that you wet a couple times in the day. the shade and moisture will aid it to cure evenly.
Me, too. Or, for that matter, what kind of a contractor makes the customer responsible for finishing his job? Who’s going to pay for re-pouring the slab if it cracks because the customer didn’t know what to do?
Did the contractor tell you to do this? If so, why not ask him the followup questions, when he’s standing right there?
I’ve seen clear Visqueen, a clear plastic sheeting used to hold in the moisture. You can pull it back to wet the concrete each day. Secure the edges with brick, big rocks or even lumber. Anything with weight to hold down the plastic.
Yep, the previous posters have it.
- Straw, burlap, etc. to keep it damp.
- plastic sheet or tarp over the top to hold the moisture in.
Here is a link that gives pretty good “layman’s terms” reasons and methods, for the “wet curing” of concrete slabs.
http://www.tkproducts.com/Curing%20Concrete.PDF
I’ll second Visqueen. I had a slab poured in 100 degree weather, and the plastic kept things wet.
I’ve seen highways poured in the dead of summer. There were sprinklers going continually with a light mist over the poured concrete. If you can’t do the Visqueen, which is also an effective method, try a light sprinkler. It’s not so much a matter of how much water, it’s a matter of having it dry slowly. That’s what “curing” is all about. You don’t want the surface to dry faster than the underlying mass. You want it all to be one piece.
BTW, concrete is amazing stuff. If handled properly it will dry and harden even if it is completely submerged in water. That’s why it is used to build footings for bridges.
Umm, I don’t get it, don’t you WANT the concrete to dry?
the water chemically becomes part of the solid structure and it is needed for it to be strong.
Umm, did you not read the last sentence in the post directly above, yours? :rolleyes:
About the footing for bridges?
Technically, no. You want it to cure.
(Bolding by me)
The harden under water, part. 
Which is analagous to curing, IMHO. 