Curing Portland Cement

[absintheisfun]

HELP!

I put in a slope to my garage (about 2 inches high, 11 inches long). Given that it is 105 degrees here in Dallas, I let it set for about an hour, sprinkled it with water and then covered it with plastic so it wouldn't evaporate too fast.

How long should I keep the plastic over the cement? I know there is a limit, otherwise it is just as bad as leaving it to dry in the heat to fast.

??????

Thanks!

 

[red]

Actually there is no limit. If kept wet the concrete continues to bond. Just that it is a case of diminishing returns (after a month the amount of additional strength starts to decline significantly) I kept my floor soaking wet for two weeks with plastic on top. Really depends on how soon you need a dry floor. Then I cut my control joints.

 

[lilredex]

Yesterday, I observed a local crew lay some "instant" curbs:



A couple of guys do some finish trowelling to make them look pretty, then a guy comes along spraying what looks like thinned out white paint*, the curbs then are left to bake in the sun.

They are also replacing sidewalk sections and the procedure is very similar. The only time they cover their work is if it looks like it might rain.

Over the years I have done many homeowner type masonary projects from laying bricks and blocks to a complete concrete driveway, one section at a time, and I never did anything special after the final trowelling. Things always turned out just fine.

I know the books alway say to keep it wet.........does it really make any diff?

My neighbour is Portuguese and his job is building overpass bridges on our highways.........will check to see what they do.

One thing I do notice is, concrete that comes off those trucks sets up and turns "white" much quicker than anything I ever mix up. A few hours vs a week for mine.

* and only sprayed on the visible front side, not on the back.

 

[Tom McDermott]

Portland Cement Association FAQ recommends that the surface be kept moist for 5-7 days.

http://www.cement.org/basics/concretebasics_faqs.asp

-- Tom

 

[bimmer1980]

RED is on track with this one.

Concrete cures with water through a chemical reaction. At a minimum, a week will get you about 50% to 75% of the full strength. It will continue to cure at a dimishing rate for the rest of it's life.....

I poured my slab a couple of weeks ago. I covered it about 2 hours after the final finishing and then I cut the control joints the following day. Then I re-wet it all down and re-covered it. It will stay covered for another couple of weeks. At 40 yards on concrete and about $4000 for my slab, I want to give it the best chance I can to cure to full strength.

There are additives that you can spray on concrete to seal the surface to keep it from drying out. THat is most likely what the road crew was doing. Curbs are a realitively low strength requirement, so they really don't care what they look like.....

 

[Black Moon]

Bimmer is right about the curing compound they spray on. Just don't ever use it on a floor you want to paint.

At least a week covered making sure it's wet underneath.

Sawcutting needs to be done within the first 72 hours and needs to be done properly (min. of 25% of depth)