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the pipe master
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Discussion Starter #1
Is there any point in spraying concrete down after the first 24 hours? It doesn't seem like the water is even soaking in at this point. It looks like the concrete is not even porous anymore and the water just sheets off and evaporates after a while.

2nd question. If it doesn't help it cure any stronger, does it do any harm?

I’m just wondering if all this water I’m using is going to a good cause or not.
 

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The water prevents the moisture in the new concrete from evaporating. Concrete needs the moisture to continue to cure and gain strength. Preventing the moisture from evaporating extends the effective curing time and can reduce surface or/and shrinkage cracks.

Your eye is not educated to analyze concrete and just because the top surface appears hard, does not mean it is done gaining strength.
 

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"Pro"
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In our Materials Testing Class (Concrete) we would have to do various mix designs that we poured into cylinders. We would leave the cylinders in a climate controlled room for 14 days then break them. The concrete would always be damp after the 14 days from which I believe was due to the purposly high humidity in the room. I believe the same applies to 28 day tests to allow it to reach it's maximum potential strength.
 

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Renaissance Man
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Yes, keep it wet as long as possible :thumbsup: - 1 week perferrably. Also depends on circumstances and final appearance. Blazing hot sun vs. damp dingy basement will require different approaches. Sheet plastic retains moisture, but can stain /blotch finish :eek:. There are also curing compounds created for this purpose. Good ole garden hose or sprayer works well too.

The idea is to keep it dark in appearance for about a week and your good to go! And too much water won't hurt unless u get a lil' crazy :w00t:.
 

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I have been on jobs were it was required a 10 day wet cure. We had to roll out a some type of fiber matting over a 1/2 mile on a bridge deck that was 20 to 30 feet wide.
 

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Renaissance Man
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I have been on jobs were it was required a 10 day wet cure. We had to roll out a some type of fiber matting over a 1/2 mile on a bridge deck that was 20 to 30 feet wide.
I hear ya, with all due respect:notworthythose engineers really love to step it up a notch - I think Hoover dam is still curing:drink:
 

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In India, where the typical apartment building is 1+3 (parking at grade and 3 stories of concrete columns and block/brick or 3 stories of block/brick), they cure the concrete floors by laying the first course of block or making a temporary concrete curb and flood it with 1 1/2" of water. They cure for about 7 to 10 days since they have high temperatures and concrete cures fast. If there are monsoons, the is no problem to get the water on the floor until the nexy floor forms are set.

The only problem is the "wet" rooms that are 1" lower and sloped to the drain rough-ins (2 sets - sanitary and gray water), so they have to plug them to keep everything from draining.
 
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"Pro"
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How does that compare to a slab baking in the Florida sun with the wind blowing over it wicking the moisture out of it?
My point was, if they keep it wet in the lab for 14 days to let it reach it's max. strength, then it makes sense to keep it moist out in the field as well, so that it's able to reach it's max strength.
 

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Gumby
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If you are going to use the wetting method for curing then it must be continuous. Moist or flooded.
Once it is dry it is too late. When hydration stops it cannot be restarted.

I have seen them start and stop the water so badly the surface of the concrete comes off. Hot windy day in Texas.
The best modern day option for large surfaces is a white pigmented cure and seal. That was what we used when I was in the Airfield business.
 

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the pipe master
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Discussion Starter #13
It has gone up to 12 hours at a time between watering. It's a 6" slab (driveway) with 4000 PSI fibercrete.

They poured it, floated it and left. I let it dry for 12 hours before soaking it down as I didn't want to mess up the broomed finish. It's been 132 hours since it the first bit of concrete came out of the truck.

It still has a dark grey look to it. The overpour (no wetting since pour) is much lighter in color. Am I still OK?
 

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Gumby
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It is what it is. Most concrete is not properly cured. So your 4000 psi slab will achieve just over 2000 psi without curing.

http://www.nrmca.org/aboutconcrete/cips/11p.pdf This is a good article on curing. Typically curing must begin within 2 hrs or less of finishing. Depends on wind and temperatures.
Improper curing can cause scaling, reduced strength, poor abrasion resistance and cracking.

Again though, most residential concrete does not get cured. Does it have proper expansion and contraction joints?
 

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the pipe master
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Discussion Starter #15
Contraction (control) yes, expansion no.

It is what it is. Most concrete is not properly cured. So your 4000 psi slab will achieve just over 2000 psi without curing.

http://www.nrmca.org/aboutconcrete/cips/11p.pdf This is a good article on curing. Typically curing must begin within 2 hrs or less of finishing. Depends on wind and temperatures.
Improper curing can cause scaling, reduced strength, poor abrasion resistance and cracking.

Again though, most residential concrete does not get cured. Does it have proper expansion and contraction joints?
 

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Gumby
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Your joints should be no further than 15' apart on a 6" thick pad. Rule of thumb is 30 times thickness. Never exceed 20'.
If not then sawcut 1.5" deep where needed but try to make it look even/visually appealing.
Cure the next one properly. You might find some cure and seal at Home D. Look for Sika.
 

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Seal it and be done with it. Water makes little difference. Perhaps in India with the high temps or with a high cement content producing a hot mix. A proper design mix will come up to strength.
 

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The idea of watering the slab is to slow the cure rate. It helps prevent craking on the top and max psi. The best way hear in florida is to have a water supply set in the house slab topped with a garden sprayer. Turn it on soon after the final finish and let it on for a few days none stop. You did a drive way not as big of a deal your compaction methods are fine prob 90% compaction and this time of year the temps dont require the water curing as much. Things will be fine. Your cuts are at a good spacing as well.
 

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US Army Corps of Engineers says:

Beginning immediately after placement, and continuing for at least 7 days,
cure and protect all concrete from premature drying, extremes in
temperature, rapid temperature change, freezing, mechanical damage, and
exposure to rain or flowing water. Provide all materials and equipment
needed for adequate curing and protection at the site of the placement
prior to the start of concrete placement. Accomplish moisture preservation
of moisture for concrete surfaces not in contact with forms by one of the
following methods:
a. Continuous sprinkling or ponding.
b. Application of absorptive mats or fabrics kept continuously wet.
c. Application of sand kept continuously wet.
d. Application of impervious sheet material conforming to ASTM C 171.
e. Application of membrane-forming curing compound conforming to
ASTM C 309, Type 1-D, on surfaces permanently exposed to view.
Accomplish Type 2 on other surfaces in accordance with manufacturer's
instructions.
Accomplish the preservation of moisture for concrete surfaces placed
against wooden forms by keeping the forms continuously wet for 7 days . If
forms are removed prior to end of the required curing period, use other
curing methods for the balance of the curing period. Do not perform
protection removal if the temperature of the air in contact with the
cocrete may drop more than 60 degrees F within a 24 hour period.
 
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