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Wet Concrete Curing and Drying Time
Concrete floors have become a staple of the building industry for their strength, durability, and the wide range of aesthetic looks possible. The initial treatment of the concrete, once it is poured, has much to do with its long-term strength and performance.
- The Importance of Concrete Curing
- How to Cure Concrete Slabs
- The Schedule Challenge
- RH and pH Assessment
The Importance of Concrete Curing
“Curing” refers to hydration, the chemical process by which concrete hardens once it is poured. During hydration, the water content in the concrete mix blends with aggregate and cement in a chemical transformation that provides the best possible strength in the final slab. That initial mix always has more moisture than the final slab will contain. As the hydration process takes place, moisture evaporates from the slab surface.
Installers use a variety of methods to help control the curing concrete process; if the slab surface dries too quickly, the overall strength and surface structure of the slab may be compromised. Too slowly, and the project schedule might be compromised instead.
When surface treatments such as staining, stamping, or various admixtures are part of the slab’s end design, this curing process must be carefully monitored to provide even color distribution, slab strength, or design depth.
It is a moisture management balancing act.
A common practice to manage moisture conditions in concrete curing slabs is to use some form of “wet curing concrete”: supplying additional moisture to manage the moisture evaporation rate or temperature of the curing concrete. There are a variety of practices that work to keep the moisture condition at the concrete surface adequate to facilitate the hydration process.
How to Cure Concrete Slabs
1. Surface Wetting
Some contractors apply additional water through fogging or spraying the slab surface repeatedly. The challenge with this method is to keep the surface uniformly wet. Dry intervals or patches can lead to crazing or cracking on the slab surface.
2. Concrete Curing Blankets
A more common practice is for contractors to place blankets over the slab surface to slow the rate of evaporation. Curing blankets are frequently composed of an absorbent fabric or paper layer that is wetted to provide consistent moisture to the concrete surface and a less permeable layer that slows the rate of evaporation.
The blankets slow down moisture evaporation but are sometimes difficult to install smoothly and evenly across the whole slab.
3. Sealers or Liquid Concrete Curing Compounds
A third option for builders is to apply a permeable or liquid curing compound to the slab surface. These products are typically brushed or sprayed on and form a membrane that controls the evaporation rate. This method is especially popular for the installation of colored concrete slabs.
However, chemicals within sealers may skew the overall chemical equilibrium that is required for the proper curing of concrete slabs, or they may interfere with final floor finish techniques or flooring application if not completely removed.
Ultimately, concrete professionals must maintain a balance that considers moisture conditions and chemical interactions so that slabs can meet specification standards. When wet curing is used to control the initial strength and bond of the concrete pour, it will affect the drying schedule and ultimately the overall project schedule.
The Schedule Challenge
Cure Concrete and Concrete Drying
Concrete Curing and drying are ultimately two separate phases in concrete slab installation. The hydration that provides the initial mix and chemical bond of the concrete’s ingredients is the first step, but in order for the slab to be properly prepared for its final finish or flooring, it must be dry according to the finished floor specs also. How does wet curing affect drying time?
With wet curing, the added moisture serves to stabilize the excess loss of evaporated water in concrete. However, surface moisture interacts with slab water vapor that migrates from the bottom to the top of the slab. Moisture in the drying process must leave the slab by evaporating from the concrete surface.
So while wet curing may address surface hydration, it may also extend the drying schedule as the slab’s internal moisture condition is kept in place by the curing methods or membranes at the surface.
Slab moisture conditions also fluctuate with changes in ambient relative humidity (RH). Even presuming successful surface curing, the water in the concrete evaporates more quickly when ambient RH is low; conversely, the evaporation rate slows when ambient RH rises.
Unsuspecting contractors may mistakenly verify the success of wet curing without truly knowing the state of internal slab moisture levels.
Free Download – 7 Things You May Not Know about Concrete Slabs
RH and pH Assessment
Luckily, concrete curing slabs can be cured safely and dried effectively by assessing both pH levels and RH levels. Wagner Meters produces two simple methods for precisely monitoring slab moisture and pH levels.
The Wagner Meters Rapid RH® is a cost-effective, precise way to assess the overall slab moisture condition once the curing process has been completed. The Rapid RH utilizes state-of-the-art technology with in situ moisture probes to measure the moisture condition at 40 percent of the slab’s depth.
These probes can be inserted into several test holes to simultaneously assess moisture at multiple slab locations. Using the Rapid RH is a timely and dependable way to ensure that the slab’s moisture condition is accurately monitored after a wet cure process has been applied.
Installers can effectively check pH levels prior to a finished floor system being installed with the pH Test Kit. The kit from assesses pH ranging from 0 to 14.0, so contractors can ensure and maintain the all-important pH of successfully cured slabs.
For a successful finish every time, wise contractors monitor the drying process carefully, assessing both moisture condition and pH. The Rapid RH and pH Test Kit are the tools to do the job right.
Learn how to overcome a wet concrete slab.
Jason has 20+ years’ experience in sales and sales management in a spectrum of industries and has successfully launched a variety of products to the market, including the original Rapid RH® concrete moisture tests. He currently works with Wagner Meters as our Rapid RH® product sales manager.
Last updated on October 26th, 2023
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I ran four sprinkler on my slab, 5 minutes every 20 minutes, for 8 days. The framing carpenters hated me, had to use red loads in the mail gun and double tap every nail.
Had 2400 SF of 4in concrete with rebar poured for a shop. The concrete company hired by the shop builder gave no instructions for wetting etc. It did rain the last few days ( starting day 5 today ) Should I start wetting with a hose over the next few days? I’m in Oklahoma with current temps in the 70s.
Had cement poured over old cement to become level with the kitchen. 2 questions: wetting the cement and when can the refrigerator be moved onto the new pour? Thanks
Glynda:
Thank you for the questions. I am not clear on what you are asking about the wetting of the concrete. The second question regarding the fridge would be one for the installer of the concrete or the manufacturer of the concrete. The answer could possibly vary depending on thickness and type of product. Good luck.
I just had 1700 sq ft rear patio deck poured. Its 4” thick 3000 psi mix. It’s been about 30 days since the pour. Most of of the main slab has cured nicely but I’m worried that there some large areas that still look like it has not cured “blotchy”. Assuming that the blotchy areas are from moisture within the concrete, do you have advice to help get the moisture out? The weather has been at an average temperature of 70 degrees mostly sunny. We have been misting it every day after a week of it being poured. I did notice that the area where this condition exists gets shade from my patio all day.
Thank you
Victor:
Thanks for the questions. First, the concrete has cured (gotten hard), so if that is the concern, it shouldn’t be. Concrete will get hard no matter the conditions, achieving 80-90% (if not more) of the 3000psi strength in 28 days. If the color variation or “blotchy” cosmetic appearance is the concern, I would guess it will even out over time. If it is a big concern you might try pushing air (fan) across the surface. Good luck.
I just had a 4″ thick rebar re-enforced 1000 ft^2 driveway poured, and my concrete guys didn’t tell me about watering the concrete, so I didn’t do this the first 7 days- even though it would have been simple for me to do. I was counting on them to provide their expertise. We haven’t driven on it at all yet. I’m in Colorado, have had hot dry weather, and I’m now worried that I had high evaporation cure. I don’t see any signs of damage or cracks, but I’m worried about the long term. I started watering the concrete 7 days after it was poured.
Do you have any advice for me?
Richard,
Thanks for the question. I haven’t seen many driveways wet cured due to their overall makeup and usage. I would think you are fine, but I would reach out and ask the concrete contractor the same question to get their response. Enjoy the driveway.
i just got the new driveway yesterday evening around 6 pm when can i start watering it
Gurdev,
Thanks for the question. I would ask the company that installed your driveway this question so they can give you specific guidance based on the materials used.
Hi
I started watering the concrete about 4 hours after being poured and it seemed like some minor parts of the top layer were starting to rip off. Will this have a negative effect in the long run? Should I wait a bit more before I can start water curing? Cheers
Bruno:
Thanks for the message. I would make sure you are using some kind of material (like burlap) to cover the concrete during this wet curing and only misting the concrete.
Hi Jason,
How long should the curing time and drying time be for an outdoor driveway? The plan is a 6″ thick slab that is rebar re-inforced as we can have heavy trucks on it. We live in Washington state, so it is rainy season from September to May. Should we wait until May or June to pour so we have a dry July to allow for proper drying?
Thanks!
Pamela:
Thanks for the question. From a curing standpoint, you can expect 50% of the specified strength of the concrete to be obtained in 7 days and about 80% in 28 days. From a drying standpoint (totally different than drying) it really depends on if you are going to put some type of coating on top of the driveway. If I were going to pour a concrete driveway, I would prefer to do it when I felt comfortable knowing there wasn’t going to be a monsoon. Good luck.
Jason
We just had a 4 inch with a 6 1./2 bag of concrete in a 16’x 24′ slab for my covered patio . The concrete has a brush finish to avoid slipping. I have been spraying it with water several times a day for the last week . We had it poured last week it will be a week old by this Friday June 19th. Is this the best way to cure the concrete? We live in meridian Idaho which is the south west part of the state. We had another salb laded and within 3 day we had cracks I am doing my best to try to avoid them. I know concrete cracks I just want to achieve a minimal amount of cracking. ghostshiled masonry sealer Siloxa-tek 8500 What ca I do to help prevent cracking. I also and going to be putting on a sealer after 30 days. It is called ghostshield lithe-tek 4500 concrete Densifier .
Fennessy:
Thanks for the questions. Many times people will wet cure a slab by putting some type of cover on top of the slab and constantly watering it at a low level of 3-7 days. I see no reason your method won’t work, although not nearly as efficient. Good luck with the remainder of the project.
It depends on the weather. If you are on the hot sun you could set up rapidly. I have had it happen to me. Fortunately we got a week of rain for a great cure. Normally I suggest the night of a day pour, then depending on weather at 1pm or so and again at night. Also it depends on the psi or slump poured. However do not wet until you have a hard set.
Very nicely explained sir
Does it still help keeping the fresh concrete wet if I applied cure after pouring?
How soon can I fog my outdoor concrete after pouring? It has been 4 hours already. Thanks.
Keith:
Thanks for the comment. You will usually see people start to mist a slab shortly after the final finish. Good luck.