Concrete Moisture: Know it's There & Know How to Deal with It

10/4/2016

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.

29 Comments

Elias Saltz

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/

You're saying that you do not like admixtures (the ones I'm aware of are Barrier One and SPG Vapor Lock 20/20). What experiences have you had with your flooring products on slabs treated with those products?

Evan Adams

10/4/2016 02:12:12 pm

Elias,

I've had latex based adhesives dissolve when they pass through silicate based admixtures or spray on curing compounds. Should they not fully react with the mix when moisture comes up you get unreacted silicates in the solution under the floor, in the blisters that develop. It is very expensive to figure this out but it is why any flooring manufacturer places the risk on the specifyer if they choose to specify these sort of products. ASTM F710 is very clear, any flooring spec that refers to ASTM F710 forbids their use.

And re: your VOC post. It misses something. The issues you and others discuss on VOC are because the science hadn't caught up. There are plenty of adhesives that are now not affected by pH and pass the VOC requirements. But it is not all adhesives. The old science failed the new VOC rules, now the new/now old VOC rules work fine with new adhesives.

Rachel Brown link

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...

Admixtures as discussed do not dry out the slab, they just hold the water in. Concrete cracks, the concrete cracks, the moisture comes right up through that crack.

Then there are admixtures that are self desiccating and they will help dry out a slab (there was a presentation at Construct about it). Such systems also have the benefit of really helping control concrete curl. (curl is water leaving via the surface, if water is used inside the slab, it curls less!)

Otherwise you can:
- look at flooring products with higher RH limits. I'm a rep and I'm not going to say names, but Erik and I both have products that work at higher or unlimited RH.
- look at finishing the slab less and specify a topical epoxy system. (you'll save money in broom finishing the surface and that will make the epoxy cost less, not free but less)
- enforce timelines. RH is done at acclimated conditions. (the use temp & rh the building will be kept at. So, get the building acclimated and plan on 1" per month to dry out once the building is at use RH & Temp. (yes hard with fast track construction) Finally, RH usually means rain. There is no better way to slow a slab drying than rain. Any time water touches the slab you have set the drying back to day ZERO. Keep liquid water off the slab.

Jerry link

2/14/2017 08:06:21 am

Barrier One and you're done. Just factor in a 50% bump to your concrete cost. That's all? Yup, Barrier one is amazing. Pricey as hell but overall it remedies all the issues I've been seeing in the industry.

2/14/2017 10:30:12 am

I disagree spray and pray isn't a fix.
And, I don't know this sites TOS, but specific brand names probably shouldn't be in posts.

Eric Lussier link

2/21/2017 04:33:55 pm

Jerry,
If you could kindly show me the science behind Barrier One, I could listen. However, not one person I've come across has been able to demonstrate it. Hence, all concrete moisture experts have DQ'd this product and technology.

Ray Webster

10/4/2016 08:32:03 pm

Re:
"Evan Adams
- look at flooring products with higher RH limits. I'm a rep and I'm not going to say names, but Erik and I both have products that work at higher or unlimited RH."

The circumstance that have been named appear to be a common thread in construction, however training and education with real solutions is not readily available to most contractors facing moisture problems in concrete. Please help me to identify products that will meet the tough environment present after a water loss.
We come across damaged floors regularly due to water losses because I am in the Emergency Services business. Could you contact me to identify if there would be a fit between your products and our customers in California?

10/5/2016 03:27:41 pm

Ray,
Please let me know if Evan hasn't gotten in contact with you direct. I would be happy to bring this offline. I can be reached at elussier at precisionathleticsurfaces dot com

10/7/2016 09:39:40 am

Ray I can be reached at Evan(remove this for spam)@westernfloorservice.com

If you are talking water damage, that is an entirely different subject from concrete moisture which has more to do with boot pressure and osmotic action.

brent redmon link

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.
It just reinforces the point that even with good design details, understanding product data and its impact on related assemblies is an ongoing education process, not just a one time exercise. In an unrelated comment - Adhesives themselves have become a bit of a challenge too with VOCs being reduced as they have.

Russell Snow link

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 rsnow@wrmeadows.com. 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

Evan,

That is great to hear that we were able to help out and answer your questions. If you have anything further, we are always available to assist.

Adam Schwegel link

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.

CSI finally released a spec section for sealing concrete for this type of work as CSI MasterFormat 09 05 61.13 Moisture Vapor Emission Control scope.

There are many publications on this subject and most provide a one dimensional (based on the writers area of experience) blue print on how to write a good project specification. Reading what water vapor emission, adhesive and any sealing product requires to meet a warranty is another area that needs to be addressed in a specification. For example, ASR is usually mentioned in most warranties, so I would recommend reading ASTM C-33 Concrete Aggregates.

Reading list for this subject may include:
1) ACI 302.2R-06 (not sure if there is a new release)
2) ACI 212.3R-10 Report on Chemical Admixtures for Concrete, if you would like to learn about silicates and ingredients used in common admixtures

A combination of products (concrete additives, vapor barriers/ retarders, concrete finishing, testing requirements and listing information related to the subject, usually works best for project specifications. Relying on moisture testing and sealing products can be costly. However, as mentioned in the Lets Fix Construction post on "What Did We Learn About Substitutions", Owners value the schedule and cost impacts to a project may not be an area of concern.

Areas of the specifications that need to be addressed are usually Division 3 Cast-In-Place concrete, Division 9 floor finishes and where you would like to specify a water vapor emission control system safeguard.

It is best to address specification updates knowing how the Architect, Specifier and Firm uses them on projects. Is a firm working from an office master? Are individual specs ever used on projects? Are specifications developed by independent specification consultants like members of SCIP.com. Once that is determined, update your specifications and have a discussion with any consultant. Division 3 may be written a structural engineer.

I hope this helps visitors of Let's Fix Construction. You may source various water vapor emission control products at www.ZeroDocs.com.

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.

Kylie Dotts link

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.

Luke L Kimble link

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”.

If the Owner/GC/Architect knows that the concrete floor is going to receive a moisture sensitive floor, then plan on using a Rapid Drying Concrete for the floor slab. Not only will this eliminate the moisture problem and need for a moisture mitigation coating as discussed here, but will also offer a high early strength, low shrink, minimal cracking and low curl, all of which will can reduce the cost of a project.

Last week I met with a flooring installer who was telling me the issues they encounter this time of year – the month before school starts and new schools open. It falls on the flooring installer to resolve the issue with high moisture in the concrete slabs that do not meet the moisture tolerance for installation…usually at the last minute and without prior warning.

Slab Leak Repair Charleston link

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.

Dean Moilanen link

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
on concrete slabs.

Imbotec Group Canada link

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.

Slab Leak Detection and Repair Charleston link

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.

24 Hour Hilton Plumber link

1/29/2018 01:30:21 am

Wow ! This is great. I love your blog. Thanks for this one.

Laura

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....

Eric D Lussier link

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?

Concrete Moisture: Know it's There & Know How to Deal with It

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