5 Tips to Help You Speed Up Concrete Drying Time

How Long Does Concrete Take to Dry?

Normally, concrete takes 28 days to fully cure at maximum strength. Concrete sets in 24 to 48 hours and will be hard enough to walk on. Concrete doesn’t “dry,” concrete cures. The rule of thumb is that you’ll need to allow 28 days of drying time for each inch of concrete thickness if the slab is under ideal drying conditions (an enclosed area with the HVAC on, meaning there is air circulation and a low ambient relative humidity).

how long does concrete take to dry
Concrete drying time is a major factor in the schedule of most construction projects. Any way that time can be shortened can potentially save 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.

How to Speed Up Concrete Drying Time Tips:

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

The Difference Between Concrete Curing and Drying

Concrete curing and concrete drying are different processes. Concrete curing is the process of hardening that begins immediately after the concrete is poured. A majority of the concrete curing process is completed after 28 days although concrete hardening continues for a significant amount of time after that.

In the drying process, excess water evaporates from the concrete. While concrete is considered sufficiently cured in only 28 days, concrete drying takes months to complete. The rule of thumb is that a slab takes one month of drying time for each inch of thickness and this is once the conditions in the space are conducive for drying (low ambient %RH and consistent temperature). Let’s look at how you can speed up the drying process in more detail.

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 this process, the concrete becomes porous. A certain amount of water from the original mix becomes part of the concrete in this process. The water that’s left either evaporates or remains in the capillaries of the concrete as water.

How Concrete Dries

Concrete dries as the water evaporates from its surface. As water evaporates, water from deep in the concrete moves through the capillaries 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

steps to speed up concrete drying process

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

These are some steps you can take before you pour the concrete that will speed the drying process.

Use the correct amount of water in the mix. If there’s too much water, there will be more water left after curing that will need to evaporate. That means a longer drying time.

Using a high cement content mix will reduce drying time, but at the risk of causing cracking due to shrinkage.

If you’re using lightweight concrete, the lightweight aggregates absorb a lot of water and slow drying time. You can reduce drying time by replacing these 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 surface and slow 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 is cured, enclose the space as soon as possible. The most obvious reason is to protect the slab from precipitation or water from any other source. The last thing you need is to add more water to the slab.

Other than protecting the slab from additional water, the other two factors that affect drying the most after the pour is ambient relative humidity (RH) and the temperature of the slab and air above the concrete.

RH determines whether or not the air can hold more water vapor. It’s defined as the amount of water vapor the air can hold at a given temperature and pressure. So it directly controls whether water can evaporate from the slab.

Enclosing the space allows you to use HVAC to control ambient conditions. And as it happens, normal service conditions provided by HVAC are also good conditions for concrete drying. In cooling mode, HVAC systems act like a refrigerating dehumidifier and will usually maintain RH around 50%, which is ideal for concrete drying. In heating mode, they lower RH by raising the air temperature, and tend to maintain even lower RH.

HVAC systems also provide good circulation. Circulation helps to speed evaporative drying by carrying moist air away from the slab, which is replaced by drier air that can absorb more moisture.

Dehumidifiers

HVAC system visualization

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

Some facilities have built-in central dehumidifiers which will speed the drying process. If necessary, you can rent portable dehumidifiers and fans.

There are many designs of dehumidifiers, but they all use one of two technologies.

The first technology is refrigeration. This works the way HVAC systems do in cooling mode. Fans draw the air over refrigerated coils. As the air cools to its dew point, water vapor in the air condenses on the coils. The water is collected and drained away. The refrigerant is pumped to a compressor where it’s compressed, and the heat is released through a heat exchanger and vented to the outside. The refrigerant is then recycled and expanded in the coils, which cools the coils. The cycle then repeats.

The second technology is desiccation. This works by blowing air over a moisture absorbing material (a desiccant). The desiccant absorbs moisture from the air and is then circulated to a heating area. The heat drives the moisture out of the desiccant as vapor. The vapor is vented to the outside and the desiccant is circulated back to absorb moisture again.

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

Testing the Concrete for Dryness

Of course, the only way to know if you’ve been successful in speeding up your concrete drying is to test the concrete for dryness. You can’t tell if it’s dry just by looking at the surface. As we’ve seen, moisture moves through the pores of the concrete to the surface and evaporates, so the surface is always drier than the center.

Concrete moisture testing has been studied since the 1960s, and researchers have developed a scientifically proven test for measuring moisture levels in a slab.

The test requires sensors for measuring the RH of the air trapped in the concrete. These sensors are inserted into the slab at specific depths. For slabs drying from one side, the depth is 40% of the thickness. For slabs drying from two sides, the depth is 20% of the thickness.

This test is called “the relative humidity test using in situ probes,” and it’s the basis for the ASTM F2170 standard. Wagner Meters provides an in situ RH testing system that conforms precisely to ASTM F2170.

The Wagner Meters Rapid RH® L6 system uses single-use sensors for speed, economy, and ease of use. The L6 sensors come calibrated and documented from the factory. Once the sensors are installed in the slab and equilibrated for the required 24 hours, repeat readings can be taken without additional equilibration time. And unlike reusable probes, the L6 sensors never need calibration.

How Do You Know When the Concrete Is Dry?

When you think the concrete should be dry, according to your best estimate, the only thing you can do is start testing. If you’re lucky, it’ll be dry, but many times it won’t be. So you give it more time and test again. How much more time is pretty much a best guess based on past experience. You continue this process until the test results show that the slab is sufficiently dry and ready to receive the floor.

The unpredictable nature of this process can cause schedules to slip and costs to mount up. Until recently, this was the best process for drying a concrete slab.

If drying cannot be completed when the floor covering must be installed, there is an option to use a moisture mitigation system. However, it is important to choose a high-quality product that can be trusted to do an adequate job of sealing the moisture into the slab.

New Technology for Data Logging and Trend Analysis

The good news is, there’s new technology that can make the art of predicting concrete drying more scientific by adding some hard data to your experience.

That technology comes in the form of data logging.

Data logging means you have automated devices installed in the concrete and around the site from the beginning of the drying process that continuously monitors conditions and store data. These devices measure concrete moisture and the temperature and humidity of the ambient air at regular intervals and store that data in their onboard memory. When it’s convenient, you can visit the site and quickly and easily collect the data with apps that run on your smart device.

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

Having complete and accurate data from the entire drying process can help you in some very important ways. First, if anything changes in the ambient conditions that might delay the drying process, you’ll be able to spot it immediately. That means you can correct it sooner, and you can more easily find out who’s responsible for it. So if there’s any delay in the schedule, you have the data to protect you from liability.

Having complete concrete moisture data allows you to perform trend analysis. Trend analysis is simply looking at the data on a chart, seeing a trend, and projecting where you think it will continue. This means you’ll be able to make an earlier estimate of when the drying process will be complete. As you gather data from more projects you’ll be able to make more accurate projections, helping you to schedule tighter and save more time and money.

The Tools for Data Logging and Trend Analysis

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

The Rapid RH L6 system integrates the most advanced data logging technology available. It uses two small battery-powered devices, the DataGrabber® and the DataGrabber with Bluetooth®, that install in the L6 Smart Sensors to automatically log data.

The DataMaster™ L6 app runs on any iOS or Android device and can download the data via Bluetooth from either the DataGrabber with Bluetooth or the DataGrabber using the Total Reader®. The DataMaster L6 app can store, display, report and email the data in PDF format. Backups are stored in the cloud and in the sensors that are installed in the slab. This all-digital data path with backup ensures the highest data integrity, accuracy, and peace of mind.

To monitor ambient conditions, Wagner Meters also offers the Smart Logger™ that can record ambient temperature and RH for 300 days of replaceable battery life or up to 12,000 readings. The Smart Logger app can download the data via Bluetooth to store, report, or email it.

These two systems provide everything you need to set up a complete concrete moisture test plus an ambient condition logging system.

Conclusion

Concrete drying time is a major factor in the schedule of most construction projects. Follow the tips in this article to help speed your concrete drying time.

The only way to know that a concrete slab is sufficiently dry is to test it, and the scientifically proven most accurate test is the in situ RH test.

Data logging through the drying process enables you to detect problems earlier, make corrections and determine responsibility – protecting you from liability.

Trend analysis helps you to make more accurate projections, schedule tighter and save time and money.

The Rapid RH L6 system provides the fastest, easiest way to perform the in situ RH test, integrated with the most advanced data logging. Ambient logging systems can also add significant information to enable you to make more informed decisions.

32 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.

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