Concrete Curing 32x48, 6" slab

[cardana24]

Hey guys,
I have been reading over threads here and thought that I would ask a specific question about my pad that was just poured today. I want it to cure the the best it can. The pad is 32x48, 3500 psi and 6" thick, they said they put fiberglass in the mix for increased strength. I am in central VA and the weather is suppose to be in the 60's during the day and high 30's and 40's at night. How wet does the concrete need to stay during the curing process? Do I need to spray it down two times a day with a garden hose, or should I be running a sprinkler on it 24/7? Is it recomended to water it for 7 days or 28? To break it down, I really need to know how wet it needs to be and how many days it needs to stay that wet. My structure is a pole barn and does not have any walls yet so I am sure it will be exposed to sun/rain/wind. Any advice is appreciated.

 

[bazzateer]

My understanding is that it takes 4 weeks to cure to a state where you can do anything on it although it will take a further 10 years to reach it's maximum strength/hardness after which it will very slowly degrade over decades.

I believe that keeping it wet for the 28 days will not do it any harm, mine's been down 21 days now and the rain has kept it wet! Either way you will eventually see some hairline cracks appear over time.

 

[pattenp]

Just keep it looking damp for at least a week. Don't flood it. Keeping it damp for as long as possible is best but sometimes it's just not practical.

 

[6768rogues]

I would put curing compound on it before doing anything else. Then after the curing compound dries, mist it occasionally. Your weather prediction is great for concrete. You don't want the surface to dry prematurely before the deeper concrete cures. With the weather you stated, it should be fine. If you have some old burlap bags or something similar, you can put them on it and keep them damp. The design strength, 3500 psi, is the strength at 28 days. After a week it will be at least half of that, so you can go on it, just don't drive a bulldozer over it.
I was inspecting a high rise building where they needed 3500 psi strength to set up shoring to erect the next story. Rather than wait 28 days to move ahead, they used 5000 psi concrete. After 7 days, the concrete had passed 3500 psi and construction progressed. Now they have really strong floors.

 

[Lambo nut]

Interesting, I have helped on numerous pours over the past 25 plus years and have only poured, screeded, bull float and either hand trowel or paddle and let cure dry. Never had a problem with any of them except the normal hairline cracks you are going to get anyway. Is the concrete not as good now days?

Kevin

 

[Rookie2]

i would saw cut it while its fresh. Seal it if you can't keep it wet.

 

[Slednut]

Just poured a 26x30 slab two weeks ago, weather is 30s and 60s. I just covered it at night with a 34x36 hay tarp to keep it from getting too cold. Saw cut it and it looks great.

 

[6768rogues]

As concrete cures, a matrix forms and pores open. A slow cure provides stronger concrete than a fast cure. Open pores allow for faster curing. Concrete curing compound closes some of those pores and makes the concrete cure slower. After applying curing compound, pores continue to open, but having closed some of them forces a slower cure. The curing compound placed on new concrete also penetrates the surface and becomes part of the surface layer of concrete, strengthening the finished product and lessening future dusting, spalling and scaling. For the best results, put the compound on as soon as you can get on the slab.
Concrete naturally shrinks with curing and aging. Control joints do what the name implies, they control cracking. Better to have a joint where shrinkage cracking occurs than have random cracks.

 

[RedBKM]

Where at in central VA?

It was 28 at my house last night with a heavy frost. I think it is supposed to stay above freezing for the next 7 days though. I wet mine down twice a day for a week but that was in 70s/50s. If you get a lot of sun you may need more.

Good luck with the rest of your build.

 

[cardana24]

Thanks for the advice guys. I'm just north of Charlottesville. I sprayed the slab down with the hose this evening and I plan on doing it twice a day for a while. Will that be enough? If that's not enough then what is a recommended curing product? I work a lot and don't have time to spray it down more than a few times a day.

 

[kj_mustang]

I hope it didn't freeze. I am west of you over near Harrisonburg and it got down to 30 Friday night. You can use a cure and seal product but if you want to put epoxy or tile down later, you will have to remove the coating. You can buy Euclid cure and seal products from A.H. Harris there in Charlottesville. I would call them and tell them how old the pour is and see what they recommend. I poured my slab two weeks ago and used a Euclid product called Luster Seal 300 that leaves a satin sheen.

 

[HunterWare]

Poured a similar 36x36x6" slab in Crozet and I just covered it in sheet plastic with taped seams and weighted edges (basically 2x4s and such in a solid line all around just outside the perimeter). That kept the concrete throroughly wet for the entire month we waited, you could see the moisture under the plastic, even and wet, the whole time. You might need hay on the top to insulate it, I'm not really sure there, but it's cheap and easy to spread a couple inches solid on top of the plastic. The control lines were cut (every 12' for me) the day after the pour and the cover was left on tight for the month. I think 12' is about the max you want to spread them, but since I have three bays and a wall 24' back in the garage that spacing made sense for me.

Good luck

 

[Angelfire]

I hosed mine down and put visqueen over it. Even with the plastic, I still had to add water 2-3 times a day. Just don't let it dry at all. Once it dries out, adding water isn't going to do anything.

 

[barks]

What did the guy who placed the concrete tell you to do? He's the one supplying the warranty.

 

[cardana24]

I hope it didn't freeze. I am west of you over near Harrisonburg and it got down to 30 Friday night. You can use a cure and seal product but if you want to put epoxy or tile down later, you will have to remove the coating. You can buy Euclid cure and seal products from A.H. Harris there in Charlottesville. I would call them and tell them how old the pour is and see what they recommend. I poured my slab two weeks ago and used a Euclid product called Luster Seal 300 that leaves a satin sheen.

I hope it didn't either. The valley is normally a few degrees cooler than over here. Thanks for the recommendation.

Poured a similar 36x36x6" slab in Crozet and I just covered it in sheet plastic with taped seams and weighted edges (basically 2x4s and such in a solid line all around just outside the perimeter). That kept the concrete throroughly wet for the entire month we waited, you could see the moisture under the plastic, even and wet, the whole time. You might need hay on the top to insulate it, I'm not really sure there, but it's cheap and easy to spread a couple inches solid on top of the plastic. The control lines were cut (every 12' for me) the day after the pour and the cover was left on tight for the month. I think 12' is about the max you want to spread them, but since I have three bays and a wall 24' back in the garage that spacing made sense for me.

Good luck

Mine seems to be staying pretty wet just spraying it down twice a day. Should I be doing more?

I hosed mine down and put visqueen over it. Even with the plastic, I still had to add water 2-3 times a day. Just don't let it dry at all. Once it dries out, adding water isn't going to do anything.

It's been in the 50s-60s here during the day. I have sprayed it down twice a day for the first two days and its seems to be staying moist. Do I need a curing agent if I am able to keep it wet?

What did the guy who placed the concrete tell you to do? He's the one supplying the warranty.

Did not talk to the guy, I hired a company to do all of the work and he subbed the floor out. He said it would be a good idea to spray it down a few times a day for the first week. From reading here I have decided that I am going to spray it down for 28 days.

 

[scarpozzi]

I just had one poured a month ago. I ordered 4000 with midrange added to it. I didn't do fibers in it because I had used steel to provide a grid for my pex (radiant heat).

I've not seen one crack yet....It's 6-8" thick. I had it poured thicker in the back to allow proper drainage to my floor drains.

 

[cardana24]

Did you do anything to help with the curing process?

 

[HunterWare]

Regarding the "watering enough", some people literally flood it. My understanding is that you want it actually wet all the time for a month or so... Not wettened at some interval. That way you know it can't get dried out, which is what you want to avoid at (almost) all costs.