How long to wait between pouring a slab and curing?

[bob_mp]

Greetings,
Looks like the slab is going to get poured either tomorrow or Thursday after a bunch of rain delays.

I am planning on curing the concrete by covering it with burlap and keeping it wet for a week.

The temps will be in the low 60s in the day, low 40s at night. 4500 PSI mix.

Would appreciate help with a few questions...

1. How soon after the finish work is done should one start curing?
2. How long does the concrete need before rain won't hurt it?
3. Should I throw plastic on it right away to minimize evaporation?

Thanks,
Bob

 

[Always_Thinkin]

1. How soon after the finish work is done should one start curing?
-As soon as you can without marring the concrete finish and continuously for the next seven days.

2. How long does the concrete need before rain won't hurt it?
-Not usually an issue. Your method of curing will protect the surface from rain.

3. Should I throw plastic on it right away to minimize evaporation?
-Yes. Answer to #1 and...Typically this form of moisture retention is how most people cure their concrete slab. Make sure you overlap and seal (Tape) the joints and secure the perimeter of the plastic. This is the second prefered way to cure the concrete. The prefered is continous wetting burlap blankets or ponding 1 inch over the slab.

 

[Cryptic1911]

Or just set a sprinkler on it that covers the entire area. That will keep it plenty wet. We did ours that way

 

[darkk]

As Slayer said, once the concrete was firm enough to stand on, I put a sprinkler out in the middle and kept all of it as wet/flooded as I could for 7-8 days. You want to keep the water from evaporating to quickly to prevent cracking. Our 30'x30'x6" garage slab was done 3 years ago, no cut lines and no cracks. The first week is the most critical, keep it wet, wet, wet..

 

[bob_mp]

Thanks guys. So would it be reasonable to cover it with plastic for, say, 4-6 hours after the finishing is done and then switch to seriously wet burlap for a week?

I was thinking of hooking up a couple of lawn sprinklers to hose faucet time and keeping it soaked.

Any thoughts for an inexpensive source of burlap?

Much obliged,
Bob

 

[Always_Thinkin]

If you are going with burlap, I personally would not put the plastic down. Go straight to the burlap. I would have it in rolls soaked and ready as soon as the finishers are done and the surface won't mar.

 

[ConCretin]

No need to switch methods. Your goal is simply to prevent the mix water in the concrete from evaporating to ensure there is plenty available for hydration and strength gain to continue. Plastic or wet burlap just seal the mix water in.

Ideally you should cure concrete until it attains it's full compressive strength but it's common to cure for 7 days, which will get you to about 70%.

You should be able to buy a roll of burlap at any construction supply house. One thing to keep in mind is that burlap can stain the concrete. If this will bother you, I'd just wet the concrete down and cover it with poly.

 

[pop pop]

Burlap +1
Plastic -1, you'll get solar heating under the plastic and overheat the slab.

 

[darkk]

When it's hard enough to walk on set up the sprinklers and turn them on. Covering it with anything is also going to leave a pattern on your concrete. Just use the sprinklers and keep all of it soaking wet for a week and you'll be fine.

 

[Ron Lombardo]

28 days for structural concrete should reach its PSI capacity ... if your using 4500psi ---28 days. 60 - 40 degrees I dont think evaporation is going to be major issue ... so just wet with a garden hose and cover with plastic

 

[camarotoolman]

I have never seen or done any of the above and never had a problem, maybe concrete is different here or because its so hot and damp?