5 Tips to Help You Speed Up Concrete Drying Time

How Long Does Concrete Take to Dry?

how long does concrete take to dryAccording to the Portland Cement Association, once conditions are conducive for the concrete to dry — that is, consistent, reasonable heat in the air and low relative humidity — it typically takes about 30 days for every one inch of slab thickness to dry to 85-90% relative humidity. We say ‘once conditions are conducive’ because concrete that was put down a year ago might have been exposed to the elements for eleven months and only enclosed for the last month. If so, it has only been drying for one month.

Since concrete drying time is a major factor in the schedule of most construction projects, shortening that time can potentially save you a lot of money.

When a flooring system will be installed over the concrete slab, drying is critical. If the slab isn’t sufficiently dry when the floor is installed, the floor might be seriously damaged by the excess moisture.

Tips on How to Speed Up Concrete Drying Time:

  1. Use the correct amount of water in the mix. Too much water can increase the drying time.
  2. Do not over-trowel or seal the surface. This can block the pores in the concrete, diminish moisture evaporation, and increase the drying time.
  3. Keep doors and windows closed, the HVAC running, and fans circulating the air.
  4. You can also use dehumidifiers to remove moisture from the air. This will speed up the overall drying process of the slab.

The Difference Between Curing and Drying

Concrete curing and concrete drying are two different processes. Curing is the process of hardening that begins immediately after the concrete is poured. The concrete curing process is usually mostly complete after 28 days or so. However, the concrete will continue to harden further for a significant amount of time after that.

Even after the concrete is cured, excess water still must evaporate from the concrete. While it only takes around 28 days to cure concrete, drying can take months. The general rule of thumb is that concrete takes about 30 days to dry for every one inch of slab thickness. However, as we pointed out above, the conditions need to be right. That is, you’ll need low ambient relative humidity and a consistently warm temperature. You can achieve this by enclosing the space and then turning on the HVAC.

How Concrete Cures

There are many types of concrete, but they all contain three basic components: cement, aggregate, and water.

When water and cement are mixed, a chemical reaction occurs that binds them together. This is what causes concrete to harden. In the process, the concrete becomes porous and a certain amount of this water becomes part of the concrete. The water that’s leftover either evaporates or remains in the capillaries of the concrete.

How Concrete Dries

Concrete dries as the water inside it evaporates through its surface. As this water evaporates through the surface, water from deep within the concrete moves through the capillaries and up to the surface to replace it. As long as the surrounding air can hold more water vapor, evaporation continues. When the surrounding air can’t hold any more water vapor, evaporation or drying of the concrete stops.

How to Speed Up Drying: Before the Pour

how long does it take for cement to set

Admixtures or the right balance of water can greatly help decrease drying times. 

There are a few things you can do before you pour the concrete that will speed up the drying process:

    • Use the correct amount of water in the mix. If there’s too much water, there will be more water left over after curing that will need to evaporate. That means a longer drying time.
    • You can use a high cement content mix to reduce the drying time. However, there is the risk of cracking due to shrinkage.
    • Are you using lightweight concrete? Lightweight aggregates absorb a lot of water and this increases the drying time. You can reduce the drying time by replacing these lightweight aggregates with synthetic aggregates that don’t absorb water.
    • If possible, don’t use curing, sealing, or bond-breaking agents. They can inhibit evaporation from the concrete’s surface which increases the drying time.

How to Speed Up Drying: After the Pour

What is the fastest way to cure concrete

After you pour, the strategy for drying changes.

Once the slab has cured, enclose the space as soon as possible to protect the slab from absorbing any additional moisture.

While protecting the slab from additional moisture is important, there are a couple of other factors that affect drying after the pour:

  • The ambient relative humidity and temperature of the air
  • The temperature of the slab itself

The ambient relative humidity is important because it controls whether water can evaporate from the slab. If the ambient relative humidity is too high, your slab won’t be able to dry.

Enclosing the space allows you to use HVAC to control ambient conditions. In cooling mode, HVAC systems act like a refrigerating dehumidifier and will usually maintain a 50% relative humidity level, which is perfect for drying concrete. In heating mode, they lower the relative humidity by raising the air temperature.

HVAC systems are also a great way to get air circulating around the concrete and thereby reducing drying time.

HVAC system visualization

To really speed up concrete drying time, enclose your slab and ensure the HVAC system is on.

Dehumidifiers

Some facilities have central dehumidifiers that can be used to speed up the drying process. You can also rent portable dehumidifiers and even fans.

Both centrally installed and portable units are available that use one of these methods.

Testing the Concrete for Dryness

You can’t tell if concrete is dry just by looking at its surface because the surface is nearly always drier than the center of the slab. The only way to know if concrete is dry is to test it.

Concrete moisture testing has been going on since the 1960s and today there’s a scientifically proven way to easily test the moisture content of a concrete slab. The test is called “the relative humidity test using in situ probes” and is the basis for the ASTM F2170 standard.

The test uses sensors — inserted into the concrete at specific depths — to measure the relative humidity of the air trapped in the concrete. For slabs drying on one side only, the sensors are inserted to a depth that’s 40% of the slab’s thickness. For slabs drying on both sides, the sensors are inserted to a depth that’s 20% of the slab’s thickness.

The Wagner Meters Rapid RH® L6 system is an in situ relative humidity testing system that conforms precisely to the ASTM F2170 standard. The single-use L6 sensors are factory calibrated and easy to use. Once they’ve been installed in the slab and allowed to equilibrate for 24 hours, you can take repeated moisture readings whenever you want. Unlike reusable probes, the L6 sensors never need recalibration.

How Do You Know When the Concrete Is Dry?

You don’t unless you test it. If you’re lucky, it will be dry. However, many times it won’t be, so you’ll need to give it some more time to dry and then test it again. How much time you’ll give it to dry before testing again is pretty much a best guess based on past experience. At some point, the slab will be dry enough to receive the floor covering. Of course, this is an unpredictable process and because of that schedules can slip and costs can mount up.

When you absolutely must install the floor covering but the drying process isn’t complete, you can use a moisture mitigation system. If you go this route make sure you choose a high-quality product that will adequately seal the moisture into the slab.

New Technology for Data Logging and Trend Analysis

Technology is now available that adds some science to the art of predicting concrete drying time.
It’s called data logging.

Data logging involves installing small devices into the concrete. These devices have the ability to continuously monitor concrete moisture levels as well as the ambient temperature and relative humidity. The collected data is stored in their memory and whenever you visit the site you can easily download it via an app on your smart device.

This data can give you important insight into the drying process. For example, if a change in ambient conditions is likely to delay the drying process, you’ll be able to spot it and correct it sooner. Of course, you’ll also be able to easily see who’s responsible for it. (Hint: It won’t be the installer.) So, if the schedule gets delayed, you’ll have the data to protect you from liability.

While the Wagner [RH] probe takes only about a minute to read, the others take 2 hours to read. So if there 20 probes to be read, I can read the Wagner probes in 30 minutes, while it takes about 40 hours to read the other type of probe. I can find better things to do than stand around and wait 40 hours in order to read those probes.
John LowtherJKL Construction

Also, when you have complete concrete moisture data, you can perform trend analyses. This is where you look at data on a chart, see a trend, and then project how you think it will continue. This will allow you to more accurately estimate when the drying process will be complete. The more data you gather from all projects, the more accurate your drying estimates will become. This will help you schedule your next steps in the construction process, saving you both time and money.

The Tools for Data Logging and Trend Analysis

Data logging for concrete drying requires a system that integrates concrete moisture testing with automated data logging.

The Rapid RH L6 system has the most advanced data logging technology available. There are two battery-powered devices that automatically log data: the DataGrabber® and the DataGrabber with Bluetooth®.

The DataMaster™ L6 app runs on any iOS or Android device and can download the logged data from either the DataGrabber with Bluetooth or the DataGrabber using the Total Reader®.

The DataMaster L6 app stores, displays, reports, and emails the data in PDF format. For data integrity, accuracy, and peace of mind, backups of the logged data are stored in both the cloud and in the sensors installed in the slab.

For monitoring ambient conditions, the Wagner Meters Smart Logger™ records both the ambient temperature and the relative humidity for 300 days of replaceable battery life or up to 12,000 readings. The Smart Logger app can then download this logged data via Bluetooth for you to store, report, or share with others via email.

Used together, the DataMaster L6 app and the Wagner Meters Smart Logger are a complete concrete moisture testing and ambient condition logging system.

Conclusion

To sum up…

The only way to know if a concrete slab is dry is to test it. The most accurate test for doing this is the in situ relative humidity test.

Data logging throughout the drying process allows you to detect drying problems early, correct them, and will aid you to determine what is responsible for slow drying. This protects you from liability.
Trend analysis helps you make accurate projections and create tighter schedules. This saves you both time and money.

Concrete drying time is a major factor in the schedule of most construction projects and when you shorten that time, you save money. Following the tips in this article will help you do that.

33 Comments

  1. Cherian mathan says:

    There were various leaks in my tank wall external side. After repair, all the repair points are having moisture content over 6% due to which I am unable to start the coating. Will blow drying the specific point help in reducing the moisture content ?

    • Jason Spangler says:

      If the ambient conditions, temperature and relative humidity are reasonable levels where they can “accept” additional moisture, then moving heated air across the surface will help (how much is anyone’s guess). Left to its own though, the ambient air may become saturated to the point that it can’t accept any additional moisture.moisture, thus eliminating moisture movement from the surface of the concrete. Also, should you stop the heated air during this time, the likelihood of the moisture moving from the air back into the surface of the concrete is high. This is one of the reasons why some type of dehumidifier is critical in this process.

      Jason

  2. Kimberley Skinner says:

    We have built a new house….well still building….we took over after the contractor was done with the drywall. The drywall was completed about late October. We didnt do the flooring until after Christmas. We came in in may almost ready to move my mom into her new house and the flooring had buckled. We someone for moisture under the floor. We’ve had plumbers and everyone out. We can’t figure out why the concrete is now retaining moisture. It wasnt before. It doesn’t flood, it sits high. Its been over 100 degrees alot this summer. We live in West Texas so it’s not humid. We just can’t get it dry. You leave something on the floor, come back the next day and it’s damp underneath. We are at a stand still. Noone seems to be of any help around here. My dad passed away so this is my mom’s mother in law house. Right now we are all living out of boxes trying to this figured out! What do we do??

    • Jason Spangler says:

      Kimberly:

      It would be easier if you just give me a call. I am in the office Monday-Friday 7:30am-4:00pm PST. Our office number is (800) 634-9961 and you can ask for me directly.

  3. Joe Ebin says:

    Jason Spangler

    As the parking lot pavement is always cracking , we are considering pouring concrete onto a parking lot area at a business park which will be driven on by cars and occasional lighter delivery-type trucks. The tricky part is closing the parking lot so the concrete product can set up properly, all without driving the tenants into despair.

    Do you have any thoughts on this process?

    Thanks

    Joe Ebin

    • Jason Spangler says:

      Joe:

      Thanks for the comment. I think your best bet would be to get in contact with a local concrete finisher and get his/her input on this. I would imagine that with some concrete design modifications (faster curing, higher compressive strength) and timing (weekend pour, holidays) you could pull it off without a hitch.

      Jason

  4. kundan patel says:

    Joe,
    we had a concrete floor done in our backyard. It has been 3 months and it still looks like patches in it. Is it because it’s not dry yet?
    i called the company and they said it’s take time to dry. They just finished sealer coat yesterday. The cement pour was about 31/2″.
    please help. this company i am not happy with. all they care for is money.

    Thanks,
    kundan

    • Jason Spangler says:

      Kundan:

      Thanks for the question. I can’t say for sure, but my best guess, based on the information you provided, is that the concrete hasn’t had enough time to dry. I hope this helps.

      Thanks,

      Jason

  5. Barry Hyam says:

    We have had a water leak in a heater pipe in our bungalow, we have concrete floors and have industrial dehumidifiers and drying fans, but still struggling to dry the floor. The drying company say they need to skim the floor by about 2 mm. Do you think this will help to dry the floor. The bungalow was built in 1988.

    • Jason Spangler says:

      Barry:
      Thanks for the comment and sorry for all of the issues. I can’t say that I have ever heard a recommendation to skim because a floor was too wet, nor do I understand how it would work unless they theorize that the excess moisture on the surface can be utilized in the matrix of the skim coat. I understand drying, so for me, I would stay the course with drying. The other way may be effective, but I’m not sure.

      Thanks,

      Jason

  6. Carlotta Matherne says:

    I have a brick floor that was flooded with about 2″ of water when a washing machine hose failed. The flooded floor lasted about 7 hours before we got home. It’s about 600 sq. ft. of brick flooring. We had a professional crew come in and remove all the old sealer about 10 days ago. They had to re flood the floors to do their work. How long should we wait before applying the new water-based sealer? The mortar between the brick is still wet. There is a visquine (sp?) barrier under the slab.

    • Jason Spangler says:

      Carlotta:

      Thanks for the comment. I really can’t give you a timeframe on how long it will take the brick to dry. I would talk with the manufacturer of the sealer and tell them the situation to get their input. I can tell you though, air movement across the surface of the brick and good environmental conditions will help the process.

      Thank you,

      Jason

  7. Denise Supple says:

    We had a leak in the hot water pipe in the cement foundation. We had the leak fixed. We had engineered wood on top on the cement which was all pulled up. The problem now is that the flooring guy will not install the new wood flooring because the moisture in the cement is reading really high. Our contractor brought in the dehumidifiers and ran them for a week. The moisture in the cement is still very high. Do you have any suggestions on how to dry the concrete? We had a leak detection company come back out and there is not a new leak. We can’t seem to make any progress.

    • Jason Spangler says:

      Denise:

      Thanks for the comment. Consistent environmental conditions (temperature and humidity), air movement across the surface of the concrete, and dehumidification are key. The problem may take longer than a week to rectify. Another option to discuss may be a better adhesive or moisture mitigation product that will allow the floor to be installed in its current condition. It may be worth the discussion.

      Thanks,
      Jason

  8. Gill says:

    Hi , don’t know anything about pointing inbetween my patio slabs .The young man put this dry ciment i brushed it in how long does it take to dry

    • Jason Spangler says:

      Thanks for the comment. Dry is a relative term and is based off of the ambient conditions. I would have this discussion with the young man that poured the slab.

      Thanks,

      Jason

  9. lolos1 says:

    We are having a similar problem with Denise Supple, crazy as it may seem. We had a water leak 16 years ago in a hallway and the water pooled in the only room that had a wood floor under the existing Laminate flooring. The leak was fixed at the time as was the only place in the laminate flooring that had buckled, in the office. Fast forward to 2018, we are doing a little remodeling in our office and we pull up the laminate flooring and what do we find?? Water, moisture, mold, disinigrated wood. Guess the flooring contractor 16 years ago missed something. Everything was pulled up 3 weeks ago and we are down to the concrete slab, our moisture readings are so high that we as well have been unable to put a new laminate floor in the room. After reading your response to Denise, we felt a little better and we purchased a dehumidifier and have been running that for 2 days, the humidity in the room seems to be rising, but moisture is leaving the room so I’m a little unclear how this whole process is actually working. We live in sunny Arizona, where record temperatures are upon us. We also have a high powered carpet dryer running in the room. I’m assuming we just need to be patient, my small project turned into a huge project that in the end will be a good thing. We had a company come out to do a leak test (just in case) and no leaks were found thank goodness. Any other suggestions you could offer would be greatly appreciated.

    • Jason Spangler says:

      Lolos:

      Thanks for the question. Yes, patience is a big part, but based on my experience with older construction (in AZ, even newer construction at times), patience may not even be enough. This may be more of an issue than just the water leak from 2002. At times, slabs are/were constructed either without vapor retarders directly beneath the slab or if they had them, they have long since degraded due to the various materials used. Unfortunately, without this retarder, moisture vapor from the soil has direct access to the bottom of the slab which can lead to issues as you describe. I would continue the process you are doing, but I would also look to have someone (geotechnical engineer?) come out and do core samples of the slab to verify there is an intact vapor retarder. If there isn’t, all that you are doing is for not. Good luck.

      Jason

  10. J says:

    Hello Jason,
    I had a problem with moisture coming up through an old slab foundation in a bedroom, I had the slab removed and re- done, added a moisture barrier and repoured the slab. How long should I wait before adding flooring like laminate or anything else on top.

    • Jason Spangler says:

      J:

      Thanks for the question. It all depends on how long it takes for the slab to dry to an acceptable level for the laminate. Concrete dries based on ambient conditions, not on a clock, per se. Reasonable air temperatures and relative humidity in the environment are more compatible with concrete drying. This being said, measuring the moisture in the concrete is the only way to know whether the conditions in the concrete are acceptable for the finish installation. I would consult the laminate manufactures installation guidelines for this specific information on what those maximum moisture levels are and the methods of measuring they will accept. Good luck.

      Jason

  11. I do like it when you pointed out that the reason why concrete takes time to dry is because the water trapped in it needs to fully evaporate first. We really want to make it so that the concrete flooring will be dry a day or two after it has been poured, so I want to know what we can do. Perhaps, we can reduce the amount of water in the concrete but not in an exaggerated way so as to avoid adverse effects. I will talk to the contractor about what we can do. Thanks!

  12. I do like it when you said that dehumidification is one of the best ways to quicken the drying speed of the concrete because it will reduce the dew point so that the moisture in the concrete will evaporate. The only problem is that we do not know how to do this since none of us in the house knows anything about concrete works. Perhaps, we can ask the contractor that we will hire since we want the driveway to finish by the time dad returns home next week.

  13. Jeff Lentz says:

    I’m kind of shocked at this article. After a pour, concrete does not dry, it cures. Moisture must be retained in the concrete for proper curing and hardening. In fact, installers often cover concrete to help it retain moisture for the required time period. For proper curing to take place, the 28 day rule of thumb is typical for standard concrete, regardless of the thickness, since adequate moisture retention promotes curing through the slab. Once cured, then removal of moisture so flooring can be installed is a later concern, which I suspect is the intent of your article. I hope nobody here tries to immediately dry their concrete as you’ve directed and then ends up with a damaged slab because they did not leave adequate time + moisture for curing.

    • Jason Spangler says:

      Jeff:

      Thanks for the comment. I am fully aware of the facts that you cite regarding drying, curing, and hydration. The assumption in this article is that the 28-day curing window has passed because most projects wouldn’t even think about attempting an expedited drying concrete drying process until the building shell is near whether tight, which in my experience, is at least 28 days. Thanks again and I will look to see about making this delineation more clear in the article.

      Jason

  14. Keitk Kirk says:

    Jason

    I just filled a sunken living room space with 7 inch’s of concrete and wanted your advice on curing time before installing Luxury vinyl tile. My concrete guy says 30 days. The floor installers are painting a rubber type membrane on the concrete first then the plastic moisture barrier then the LVT. Do you think 30 days is enough time in our air conditioned home for curing, I was leaning toward more time maybe 60 days, its a real inconvenience but we want to make sure the new concrete has cured.

    Appreciate any advice, we are in Florida and keep our inside temps around 74 in the summer.

    Keith

    • Jason Spangler says:

      Keith:

      Thanks for the questions. Curing and drying are two very different things. Your concrete guy is correct on the curing side. Usually, it takes about 30 days for the concrete slab to reach about 80% of its specifics structural strength (curing), but there is still plenty of water left in the slab to dry to an acceptable level for the finished floor product. The flooring system you are installing should have maximum recommended moisture levels within their written installation documents. I would consult this and then perform the appropriate moisture tests to ensure you are within those limits. Good luck.

  15. Ray Medrano says:

    I am building a redwood party fence in the backyard. I hear it take 24 hours for the cement at bottom of wooden posts to dry and harden. Is there an additive at hardwire stores that quickens the drying time, say in 4-5 hours?

  16. Jim Rosasco says:

    Jason,

    My question isn’t about moisture but maybe you have an opinion.

    I just poured a 3 1/2” thick 7’ x 4’ slab with #5 rebar spaced at 8” in both directions suspended 1” from the bottom. The slab is going to cover a 6’ x 3’ block septic tank for my hunting camp. I know that’s a small tank but I’m the only one that will be using the camp. Do you think 28 days will be long enough for the slab to cure before it can be lifted into place? The slab was poured on the ground and framed with 2x4s, I put a plastic sheet underneath before the pour. I used Quikrete High Strength concrete mix from Lowe’s. It will be exposed to the elements but covered with a plastic sheet. My camp is in central Florida.

    Thanks

    • Jason Spangler says:

      Jim:

      Thanks for the question. Based on the specs, properly proportioned Quikrete High Strength is rated at 4000psi. Comparing it to a tilt wall construction process, 3000psi seems to be about the only technical number I can find that may have some relevance here. With that, 28 days seems to be reasonable. One thing you need to be careful of though is moving the slab, no matter the compressive strength. I would do some research on tilt wall placement to get some pointers. Good luck.

  17. Hi,

    Long story I’ll make it short. The flange under our toilet broke off clean from the bend. I went to hardware store bought ready mix concrete patch to fill the small space around the bend. Do to the fact The bend is still intact with no damage I need to drill the flange into the concrete8 for toilet bowl to be held down. I poured it at 2 pm and left it to dry it’s been about 4 hours and is still drying. So my question is there a better Process To help accelerate the pro cces! Thanks

    • Jason Spangler says:

      Arturo:

      So based on this situation, you don’t care about dry, you care about hard so you can drill into the concrete. Depending on the type of mix, you may be able to drill in a few days. Good luck.

  18. It was interesting when you talked about how mixes with high cement content are able to dry more quickly after they’re poured. My husband and I want to have a concrete driveway installed for our new vacation home since we think that would look more elegant than the current gravel one. Asking about cement content should help us find a knowledgeable contractor for the job, so thanks for sharing this info and giving me the idea!

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