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When our drive was poured the next morning it was covered with a 6 mill black plastic cover. The moisture was trapped under the plastic and gave it an even covering. After 3 weeks the plastic was lifted off and the cure was perfect in the 28-30 day period. Looked beautiful and has held up perfectly with no cracking.
OP if you don't put a fine mist of water on it every day the surface will dry faster, not evenly through the whole pour. It will be be susceptible to surface cracking.
Contractor was highly reccomended and gave a 1 year guarantee on any issues. Didnt tell us to water so im
Not gonna do this then screw up any warranty. If it cracks its on his dime
We just had a ton of concrete work done at our house (extending the back patio to 1100 square feet and widening and lengthening the driveway). The driveway has an exposed aggregate finish so it doesn't look like your photos, but our back patio DOES look like your photos. I'm not worried about it (it's been 36 hours or so).
Our contractor said nothing about watering it so we're not going to do it either. This is a very good contractor who has done tons of other remodeling on our home so I trust her judgment.
I live in an area that has had a major construction boom over the past twenty years. I've literally never seen anyone EVER watering any concrete after a pour. And I haven't built a home but my parents have built about 5 custom homes over the years and never watered their concrete in any of them.
I sold real estate for several years in this area (northeast Texas) and can count the times that cracked or flawed concrete was an issue, on one hand with fingers left over.
Ours was covered with plastic for 24 hours by the way, but afterwards our contractor came out and inspected it and told us we could take the plastic up.
Yes KathrynAragon lots of people have techniques they believe in You are right, I don't see very many people waterinng concrete after a pour. To do so would often require the contractor to pay someone to come back and do it. Sometimes guys who come back to pull forms will wash off the surface when they are done.
I think it is known that concrete that releases its moisture more slowly will achieve a higher compressive strength. I don't know if it is a significant difference though. I also don't know if wetting the surface actually slows down the curing process my guess is covering with plastic might be more effective.
So my opinion is sure, mist down your concrete every few hours for at least a few days starting about 4-6 hours after its poured especially if it's in the sun. The contractor will be unlikely to come back and do it. Will it make a big difference? I don't know but it cant hurt you may end up with a slightly stronger psi.
The only other thing I'll mention in regard to the OP is that if it was a real hot day, sometimes the concrete gets away from the finisher - gets too hard before he can finish - and they will sprinkle water on the surface to be able to work it up. This almost always leaves marks where the tool was used - areas "bleached out" It kinda looks a bit like the finisher may have resorted to using water there on your pour with his trowel, and also with the edger. These areas often blend in eventually but are unfortunate and different than "mottling" which I see elsewhere in your picture which is normal and will definitely fade away in a few days.
Last edited by mauialoha; 08-28-2016 at 09:02 AM..
[quote=carcrazy67;45286524]It is important to keep the concrete wet for several days. If you don't it will likely crack. Concrete achieve 95% of its maximum strength in 28 days.
We had concrete poured in the middle of May and we kept it wet for nearly a week. It has small cracks in it. We'll see what happens over the winter.
The concrete contractors wanted to put a water seal over it a day after the pour but I wouldn't let them because we're going to acid stain it sometime within the next couple of weeks. We were told to let it cure for about three months before we do it.
Your concrete needs a couple of days to totally dry out and we had that uneven color for a few days. Ours was poured in chilly wet weather.
I haven't seen a concrete pour yet that hasn't had cracks and imperfections in it. It wasn't my first choice for our side walks and patio, but the stone I wanted would have been about three times the cost. I'll take a nice trip on that dime and live with the cracks.
Just because contractors don't mention watering the concrete doesn't mean it's not a good idea. You'd be surprised how many people who've been in the trade their entire life don't know as much as a college freshman about the chemical properties of cement and the process of curing. And even those who do know usually don't care very much, because once it's poured and they're on to the next job, it's not their problem unless something goes really wrong - which they know is rare.
It's important to understand the difference between drying concrete and curing concrete. Most people use them interchangeably, but not only are they not the same thing, they're complete opposites. "Curing" is a chemical process involving hydration, which is a chemical reaction between water and cement. Without water, the chemical process of hydration stops, and once it's stopped, that concrete can never be properly cured. You do not want your concrete to dry - that's the worst thing that can happen.
Now, most concrete is poured with enough water mixed in to properly complete the curing process. Just the moisture in the mix is usually enough to give you a good slab, especially since most home pours are more ornamental than functional - it's not like you're going to be driving hundreds of 18-wheelers a day across your patio. However, if you're pouring in a hot climate - especially a hot, dry climate - the surface of your slab can dry out before that layer has time to properly cure, and if that happens, the surface is never going to be good. You could have cracking, flaking, and spalling the entire life of the slab, and the only real fix is to tear it up and pour it again.
So yeah, it's a very good idea to keep the surface of your slab wet for at least the first several days - certainly the first 3 days, and preferably the first 7. Especially in the summertime. Someone upthread said that they did that and still got cracks, and yeah, that happens. That's certainly still possible. But by properly curing the concrete, you're making it a lot less likely that you'll have any problems.
As much money as people spend on concrete slabs, I can't understand why so many people wouldn't take 30 seconds to google some information. You're going to be looking at and walking on that slab ever day for the life of your home; why would you not do everything you can to make sure you understand how to care for it and get the most out of it?
Moist Curing
Probably the best method for curing concrete, although sometimes the least practical, is to flood the surface continuously with water for the first week after placement. Do not let the concrete dry out. Contractors sometimes will recommend to a homeowner to wet a new driveway during its first week. But, if concrete dries between soakings, this alternate wetting and drying may actually damage the concrete. If you are going to water cure, keep the sprinkler going continuously for at least one week.
I have literally NEVER seen this done, but maybe it happens in some Concrete Utopia I don't know about.
From this same source:
Quote:
Concrete Strength The amount of water in concrete while it is being placed is normally more than needed for curing. However, concrete that dries out too quickly may not retain enough water for the hardening process -- a chemical reaction called hydration.
Temperature greatly affects hydration. While hot weather can make concrete harden and gain strength faster, it ultimately leads to a weaker concrete than one which has been kept cool (50 to 70 degrees Farenheit) during its first few days.
The goal is to keep concrete cool and moist so it gains strength slowly, but efficiently. Laboratory tests show that moist-cured concrete can be twice as strong as concrete cured in a dry environment.
You'd be surprised how many people who've been in the trade their entire life don't know as much as a college freshman about the chemical properties of cement and the process of curing. And even those who do know usually don't care very much, because once it's poured and they're on to the next job, it's not their problem unless something goes really wrong - which they know is rare.
Wow, that a very uncharitable statement - one I would say, in my experience, is untrue.
The overwhelming majority of tradesmen I've met over the years care very much about doing quality work. Now I will say that I speak of licenced contractors of which I am one, and also craftsmen who have gone through training and an apprenticeship in their trade which I also am one having previously been a member of Bricklayers and Allied Craftworkers for over 25 years.
If you're speaking of someone hired out in front of Home Depot, well then we have nothing to discuss. But actual contractors? There is no way some college freshman who has been taught from a book about curing of concrete knows anything about the various issues encountered on the job.
If anything, skilled craftsmen go overboard in trying to think of the most effective way of dealing with the various conditions encountered on each job.
Like I said in my post which was just two above yours, we *do* know that concrete which cures slower will end up with a higher psi (pounds per square inch) How do we know this? Every masonry worker learns this number one and also, most of us have worked on many large jobs where compression tests are run. We fill cylinders and after a week, and again after a month, the cylinders are crushed with a machine. The machine measures the psi and usually you find the concrete reaches 90% of its ultimate psi after only 7 days.
I've been on jobs where the concrete was kept cool, and covered with plastic for quite some time after the pour. But heres the thing - this was for slabs that would hold up huge machines. The contractor had to follow building guidelines so the final psi could be guaranteed to support the load.
And that the point that I tried to politely make above - yes you may be able to achieve a sightly higher psi if you wet down your concrete for a week, but if you are doing a sidewalk or driveway that will have a car or small truck as its maximum load, the concrete will probably be fine without the wetting down.
Cracks by the way are a failure of tensile strength, not compressive strength and are dealt with by installing control joints or cuts, and by reinforcing with steel.
So yes, we contractors understand how concrete cures, and yes we do need to get the job done right and in good time to be able to make a living. Part of our job is balancing thoroughness with efficiency. This you learn over the years on the job, not in some freshman engineering class.
Dave
Last edited by mauialoha; 08-28-2016 at 01:59 PM..
Concrete never dries, it cures. Hardening is a chemical reaction that only takes place in the presence of water. The surface will eventually start to look uniform. The contractor probably sprayed a sealant on the wet concrete just to keep it from drying too fast.
the water actually greatly increases the hardness of the cement. If you pay attention and watch the never ending construction on the BQE you would see that the cement is watered continuosly after it is poured.
remember that cement dries from a chemical reaction and not from water simply evaporating like paint.
you really dont know what you talking about
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You are right, I don't see very many people waterinng concrete after a pour. To do so would often require the contractor to pay someone to come back and do it. Sometimes guys who come back to pull forms will wash off the surface when they are done.
