Contributed by Eric D. Lussier
I’m quickly approaching eleven years working in and around indoor flooring, focusing mainly on sport and synthetic surfaces. Eleven years of projects of all shapes and sizes ranging from 250 square foot residential basements to 30,000 square foot college field houses. Eleven years of existing conditions, renovations, rehabilitations and new construction and the one constant that rears its ugly head on almost each job are substrate conditions, and especially concrete moisture. Conversely, said moisture issues are seemingly new news to whomever I am working with: whether that is architects, construction managers, general contractors or end users.
There are more than a few instances that can lead to high moisture in a concrete slab. Whether it is an over-watered pour, a lack of a quality vapor barrier, a compromised vapor barrier, or a missing one entirely (either from degradation or lack of placement), a fast track installation with insufficient time for the concrete to dry, an inoperable or missing HVAC system or a handful of other events. No matter the occurrence, it can all equate to the same headaches after the fact. Normally fingers are pointed, voices are raised, materials are ripped out and unnecessary time and money is spent to potentially repair or replace flooring that perhaps should have never been installed to begin with. Industry-speak may call it “flooring failure” but most of the time the flooring is performing exactly as it is supposed to. The adhesive on the other hand, may be completely failing.
New construction technologies have our buildings tighter than ever. With the use of a proper vapor barrier removing the ground from the equation, concrete moisture has no place to go but up and through the slab. When placing a fully adhered, non-breathing floor, such as a heat-welded sheet vinyl on the slab, concrete moisture in an untreated slab travels up and out, trying to push through the adhesive and new floor in the process. Even though the norm in the industry has raised from 3 lbs. of moisture to 5 lbs., as per ASTM F1869-11 (Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride), that limit can take substantial time to achieve when it comes to new construction.
Speaking of norms in the industry, thankfully most flooring manufacturers have moved away from recognizing calcium chloride testing (which is more of a snapshot of what is happening emanating from just the top of the slab) towards in-slab relative humidity (RH) testing (what is going on inside the slab). Testing as per ASTM F2170-11 (Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using In-Situ Probes (has become easier over the last handful of years with developed equipment, including testing probes that can be left in the slab and reusable digital probes. It is always recommended that an independent third-party is specified to test the concrete for moisture and not the General Contractor or flooring contractor themselves. It could be viewed that each party has a vested interest in ensuring that results are swayed their way. If you are looking for a certified concrete moisture testing party, the International Concrete Repair Institute offers a moisture testing certification program and you can search the certified testers here.
What is extremely important to note is that any concrete moisture testing is purely a snapshot in time as to what is going on in (or, on) the slab at that point in time only and passed results does not guarantee that concrete moisture will not become a problem in the future.
Are you looking to cure the concrete moisture blues? There are solutions on the market. The cheapest, yet perhaps slowest solution is normally waiting for the slab to dry, however, you may have heard of the expression time is money. Abrading the top layer of the slab may help speed up this process, however most floor coverings require a smooth, steel trowel finish for installation, so the abrading would have to be treated in some way, which may include being patched with a Portland-based cement. Solutions also include topical moisture mitigation systems (reference ASTM F3010-13 Standard Practice for Two-Component Resin Based Membrane-Forming Moisture Mitigation Systems for Use Under Resilient Floor Coverings) and some of these topical solutions can be installed within days of concrete placement and up to 100% relative humidity. Flooring manufacturers have also adjusted to the moisture issues in the industry by offering solutions such as on slab moisture barriers, flooring with textile-backing & adhesive systems, 98% adhesive free installations or adhesives that allow a very high rate of moisture vapor emissions. One of the newly recognized solutions is what is being deemed a scientifically engineered rapid-drying concrete. Please note that concrete admixtures are not listed as a solution herein, nor are they recommended by this author, nor most flooring manufacturers.
The one true method to ensure a proper floor installation is informing yourself and knowing your trusted advisors. You need to know the flooring you've specified, know the flooring manufacturer's approved adhesive, know the threshold of concrete moisture vapor emissions, know the moisture testing methods and protocols and companies that provide them, know the time constraints and perhaps most importantly, know the flooring manufacturer’s representative and the flooring installation contractor. Flooring manufacturers’ and professional reputable flooring contractors will have a business reputation and it is in their best interest to uphold it. The manufacturers and contractors should be grilled, have references checked and should be able to corroborate their claims.
There is no tried and true answer or solution when it comes to concrete moisture. Please know that moisture is ALWAYS present in concrete slabs and by accepting it is there and knowing how you can treat it or live with it is your best bet.
10/4/2016 12:00:49 pm
I provided some background on the rule changes the EPA to the VOC content of flooring adhesives in my blog early in 2015. See https://skepticalspecifier.wordpress.com/2015/01/22/how-much-do-specifiers-know-about-the-voc-flooring-adhesive-rule/
10/4/2016 02:12:12 pm
10/4/2016 04:36:30 pm
We've found that we have issues with concrete slabs drying because of the high relative humidity in the air down in southern Louisiana. While we have been warned against using admixtures because of reactivity and warned that it is basically impossible to dry out a slab in any reasonable amount of time, we are left with no real viable solutions. We've been told to specify testing by a third party independent testing agency, but the testing doesn't help us know what to do to actually dry out the slab. Do you know of any realistic suggestions for drying slabs in high humid areas?
10/4/2016 05:36:58 pm
I'm in California so I don't know too much about high RH areas (lucky me!) ... but...
2/14/2017 10:30:12 am
I disagree spray and pray isn't a fix.
2/21/2017 04:33:55 pm
10/4/2016 08:32:03 pm
10/5/2016 03:27:41 pm
10/7/2016 09:39:40 am
Ray I can be reached at Evan(remove this for spam)@westernfloorservice.com
10/5/2016 09:37:48 am
This is a big deal that needs much more attention than it gets. We have lost several two component floors that have only one thing in common - slab moisture. Although poured in the same two year window, they were installed by different Contractors uder the guidance of different Architects. In an interesting observation, they all stated failing in the same three year time frame post construction.
10/5/2016 11:09:25 am
Great post Eric! Obviously proper selection and installation of an underslab vapor retarder can help address some of the moisture issues that you mentioned, but is only part of the solution.
10/5/2016 11:11:52 am
Thank you, Russ. While true, what about on renovations. We are on a job RIGHT NOW that has a 60 year old slab and readings at 91%. Is there a vapor barrier there? Was there one there? Is it in shambles? In renovations, which is well over half of our work, there is just no way to tell if a functioning vapor barrier is there. And without the ground taken out of play (a great line that I have borrowed from Peter Craig), the ground moisture will forever be travelling through the concrete slab.
10/5/2016 11:24:19 am
I agree Eric and is one of the issues we are looking at right now from a manufacturer's standpoint. There are so many materials that are marketed as a "topical vapor retarder" or similar description that may or may not work. There are products out there I have seen to be successful, but their success is dependent on the amount of moisture that is present. I have even seen recommendations for use of crystalline waterproofing being used in this sort of application. You make a good point that the measurement is only a "snapshot in time", which is true. Is the topical material going to address the moisture drive enough that the flooring material will have no issues? That's the question. We were asked about a similar project where the readings were similar with a wood floor that had severly buckled. Their solution....remove the flooring and go with a polished concrete system. Not always desirable, but was in this situation.
10/5/2016 02:26:20 pm
The products that we work with can be put down at a different spread rate, dependent on moisture level. Many can be spread up to 100% RH concrete moisture and for the insurance, we estimate at that spread rate to guarantee that there will never be an issue down the road.
10/5/2016 02:33:49 pm
Thanks Eric. Would you please reach out to me outside of this blog and let me know what products you are working with? I am asked for recommendations sometimes and would like to provide a solution that would work. My email is firstname.lastname@example.org. Thanks
10/5/2016 02:52:22 pm
Russ, the curing compunds is something I've found the WR Meadows rep here very helpful on this subject. I'm so glad to see you all are monitoring this. I had a question about ASTM C309 & the VO Comp-20 & 1100-Clear. For me, that ASTM C309 standard has become standard in our specs as I can usually rely on such products not having lithium, potassium, or sodium silicate components that cause us flooring people issues when they get moisture coming through the slab. (it is usually gone by the time we do our normal sanding floor prep & it has had 8+ months in UV) Your rep out here did a great job getting me an answer for this & it it is what I now refer GC's and Designers to when there is a question on curing compounds.
10/6/2016 08:24:29 am
10/7/2016 10:00:06 pm
Its been my experience, there is a gap between project specifications, means & methods, practical knowledge of related materials, how trades look at craftsmanship, working with the complexity of concrete and mother nature all play a role in concrete water vapor emission issues for flooring.
10/7/2016 10:31:27 pm
Great comment Adam. Thank you very much for reaching and chiming in. Please let us know if you'd like to contribute! From that comment alone, I think you would be a great candidate.
7/6/2017 04:18:22 pm
It's interesting how you said that because of vapor barriers the concrete is less likely to get moist. I imagine that in order to apply this kind of coating you would need to do a coating removal first so you could apply the new layer. Keeping your concrete dry is probably a good way to keep it from cracking and breaking so this would be a great thing to invest in.
7/27/2017 05:31:36 pm
There are now several companies offering Rapid Drying Concretes that can be used to eliminate the problem of excessive moisture in concrete. The 2nd generation Rapid Drying Concrete is available and producible by most ready mix suppliers. The key to using these Rapid Drying Concretes is PLANNING and early involvement of the ready mix supplier and a consultant that knows how to “Bridge the Gap between Division 3 and Division 9”.
7/31/2017 02:46:21 am
The biggest problem for decorative concrete with a lot of moisture moving through a slab is the pressure it exerts at the surface. If there is too much moisture in the concrete, and an impermeable layer is placed over it the moisture migration can laminate the coating. Leak repair contractors deal with this kind of problem in a very effective way.
8/7/2017 09:12:18 pm
A very informative blog...and the various comments were illuminating as well. I was wondering if any of you "out there" are seeing or hearing of an increase in ceramic tile and stone installations, with regard to moisture issues
9/30/2017 12:51:09 am
Thanks for writing such a great post! It is amazing and wonderful to visit your blog. It really gives me so much helpful info regarding construction industry.
11/30/2017 02:51:05 am
Leaks under the tiles can'e be plastered by own , for this you need to hire an expert who can first remove the tile fix the leak and then again put the tile over it. Through this procedure these leaks are fixed properly.
1/29/2018 01:30:21 am
Wow ! This is great. I love your blog. Thanks for this one.
4/9/2019 04:21:25 pm
I have a situation where a condo unit (new) exploded in mold 3 months after the buyer moved in. The RH was 76% +/- . We installed 2 commercial dehumidification units to mitigate the interior air quality. My question is, since the condo is still under warranty, what fixes are available now that the slab has 9 condos sitting on it? Rapid RH sensors installed throughout the condo show 99% RH and we're on year 3 since the condo was constructed. I'm really struggling to find information on what fixes are available for shoddy work that is already covered up? Natural Resources Dept shows a map with an underground spring directly under the condo if that helps. What are the long term reprecussions to the unit? What should we be prepared for if this can't be fixed? Help would be so appreciated....
4/9/2019 04:31:06 pm
Laura, I'm not an interiors or concrete specialist by any means, but have worked in mold in the past. You may have two distinct scenarios going on there. I don't know where the condos are, but interior RH of 76% is high and could be faulty HVAC contributing to that. With 99% Rapid RH readings, that to me says that you have no vapor barrier, or improper one, in place. Without a vapor barrier in place, concrete moisture will always be an issue, with or without a spring underground. Is there a way for someone to perform at least one core samples of the base slab to confirm placement of a vapor barrier?
4/27/2020 06:06:38 pm
Hi Eric, The HVAC system in place is just the bathroom fan that is vented to outside. The builder said the 4 inch space in the bottom of the bathroom door is enough for the two bath fans to draw and move the air in the 1650sf condo if the doors are closed. We suspect that the vapor barrier is faulty. The area is a wetland so we also suspect a spring under the condo. Does a core test give a full picture of the condition of the vapor barrier? Thank you so much for writing. I'm not an expert, just a daughter trying to help my mother who is disabled and displaced while I worked with some HVAC people to get the humidity under control. They installed (2) commerical dehumidifiers suspended from the ceiling, sensor, and 8 or 9 vents throughout the condo and tapped into the waste line to dispose of the water. That has brought it under control but the slab is still soaked (Rapid RH, reading HI in all 4 holes drilled). We've hired a concrete specialist and an attorney since the builder says he did everything perfectly. Do you have any other test that I should explore along with the core test? You are so kind to help!
4/27/2020 05:48:12 pm
Concrete construction is an important aspect but have to give importance to the moisture content in the floors. We have known the moisture in the concrete. Now after knowing this we have to tackle with this. This amazing article shows the way to tackle with problem. This gives the solution of this moisturisation issue. Thank you so much. One must check this Moisturebarrier.co.nz it gives us more info on this topic.
6/18/2020 06:51:43 pm
My husband and I want to install a fence around our property and are trying to learn more about concrete so we can buy some ready-mix and fill in the post holes ourselves. We're hoping that we will have some leftover for some garden stepping stones if we do so. Your information that we will need to be careful of over-watering and not letting it dry entirely is very helpful!
9/7/2020 01:59:37 am
All the best things on concrete moisture know and how to deal with it. I loved reading this article. Such articles are not only knowledge enhancers but also very interesting to read and to learn to compare from.Great to find Insultech.co.nz which has same kind of wonderful tips, if possible then visit.
10/29/2020 02:16:44 pm
I have recently installed weld vinyl over vapor locvision 2020 has anybody had any experiences with this product iBooks like it is failing
10/29/2020 03:42:55 pm
5/3/2021 08:09:21 pm
2/9/2022 06:49:58 am
Slab-on-grade is the term used to describe the bulk of commercial and industrial structures that are built using a concrete substrate put on prepared soil. Based on the results of various ASTM test methods, floor covering manufacturers, whether manufacturers of tile, wood, carpet, or high-performance floor coatings, publish the maximum allowable moisture content of the concrete over which their flooring products can be installed. Whether the slab is new or decades old, and regardless of the location, floor moisture and moisture vapor can be a source of concern. The actual science is still in its infancy.
5/23/2022 06:38:16 am
Slab leaks a fact of life in areas were soils are unstable. Homes are built on concrete slabs or using pier and beam construction because basement walls can crack and break from the pressure of shifting soils. Sometimes the plumbing joints leak or the pipes crack beneath a slab, and then you have one of the most serious problems you could imagine a slab leak.
One of the most common problems with concrete is moisture. Moisture can cause the concrete to crack, flake, and chip. It can also cause the concrete to become uneven and weak. If you suspect that your concrete has moisture problems, there are a few things you can do to test for moisture.
12/13/2022 02:15:51 pm
With the use of a proper vapor barrier removing the ground from the equation, concrete moisture has no place to go but up and through the slab. Thank you for making this such an awesome post!
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