ASTM F 2170 Relative Humidity testing measures moisture INSIDE the concrete instead of just at the surface so its the bets way to predict future potential moisture problems in concrete slabs. It is less temperature and humidity sensitive and takes less time than the calcium chloride test.


Grinding the slab in a 20 x 20 area is a must before placing calcium chloride tests.  Failure to do so can result in a false low reading. Photo courtesy of George Donnelley.

It’s hard to believe this column starts my seventh year writing for Floor Covering Installer. My first column: “Concrete Moisture Problems: Causes and Detection” was published in October 2003 and it has been my pleasure to continue this work since then.  I appreciate the support of you, the FCI readers and thank you for the many positive comments and questions you have sent my way.

Each year FCI publishes this special issue on subfloor and substrate preparation and it’s jam packed with good information that can help you on a regular basis.  Make sure you hang on to this issue for future reference.  Its been said countless times that the new floor is only as good as what’s under it and that is true on all flooring materials, not just resilient.  However, because resilient floors are more flexible and have a smoother finish than any other flooring products, our side of the industry has to deal with substrate issues more than any other industry segment. 

I constantly receive questions about floor covering issues and I’d say most of them of them are related to a variety of substrate, subfloor and jobsite issues.  Here are some of those questions, some quick answers and resources on where you can learn more.



Temperature can affect resilient flooring products such as this vinyl plank floor that was installed when the material and the job site were very warm, so the material was stretched slightly during handling an installation. When the job site cooled to normal temperature, the material returned to its original size and this gap was the result.

Q: How important is temperature at the time of installation?

A: Whether it’s a residential or commercial project, new construction sites often don’t have controlled air. The HVAC (Heating/Ventilation/Air Conditioning) systems are one of the last things to become operational.  Even in the case of renovation projects, the HVAC may be turned off to save money.  And, in the case of many “green” projects, the HVAC systems are not activated until the end of the project in order to keep dust and other contaminants from getting into the system and possibly polluting the indoor air.

So, what’s the big deal if you are installing resilient flooring in these conditions?  It’s common knowledge that floor covering products such as wood are temperature sensitive so there is usually no argument about temperature when those products are being installed.  However, temperature can also affect other flooring products such as resilient flooring and even carpet, and all types of adhesives are also affected because they can set up much faster when warm and take longer when cold.  As far as the material itself, a carpet installer I used to know always said, “Acclimation is the foundation of a beautiful installation.”  That is so true. Floor coverings just install more easily if they sit on the job for a couple of days.  If they don’t there are several possibilities for failure of the products themselves, in addition to what we I said about adhesive.

Under warm conditions, many resilient flooring materials, wall base and moldings can “grow” or be stretched during handling.   They get installed with nice tight joints and when the HVAC goes on, everything cools and the flooring goes back to its original size.  The gaps that result are often blamed on “shrinkage” but it’s all about temperature. The opposite can occur when the building is too cold.  If the material contracts slightly before being installed and then returns to its original shape after installation you can get puckering joints.  So, if you are being asked to install under conditions that are outside the published guidelines of the floor covering or adhesive manufacturer, then “the word warranty is not in the conversation,” as my friend and regular reader Marty Murdoch of M.E. Sabosik and Associates in New Jersey always says.





Trowel notch recommendations are very important in resilient flooring installations.

Q: If the pH limit is 10, is 11 OK?

A: This question comes up a lot in discussions about moisture and pH on concrete slabs. Remember, “All concrete slabs shall be tested for moisture regardless of age or grade level” and “Concrete floors shall be tested for pH prior to the installation of resilient flooring.”  These requirements are per the industry standard ASTM F 710 and virtually every floor covering and adhesive manufacturer.  Please understand this is not negotiable.  If you have a failure and the floor was not tested you are liable, period. As far as pH, that is a measurement of acidity and alkalinity. ASTM F 710 states “Readings below 7.0 and in excess of 10.0 have been known to affect resilient flooring or adhesives, or both.”  Some adhesive and/or floor covering manufacturers have an upper limit of nine.  All of that being said, the answer to this question is a definite no;  pH measurements increase on a scale of ten. Each number up is 10 times more alkalinity than the previous number.    Even though one point on the pH scale may seem only a little, it’s actually ten times higher with each point up the scale so it’s actually a VERY big difference going from 10 to 11.  It’s huge.  If you are over the limit it may be a sign that there is moisture present and when you have high moisture and elevated pH that is a recipe for disaster because the adhesive can’t handle it.  Stop everything and call the adhesive manufacturer to see what they recommend for handling the problem.





Acclimation and site temperature can prevent gapping in resilient flooring.

Q: Why can’t I use lauan?

A:  In my July 2007 column (The Experts agree: There are better choices than Lauan for Resilient Underlayment, FCI July 2007) I covered this question at length. Lauan is still being widely sold as underlayment even though there are dozens of superior products that have strong manufacturers’ warranties for use as resilient underlayment, which lauan does not.   Underlayment grade plywood and fiber reinforced panels are harder, more stable and more consistent in thickness that lauan.  What do the experts say?

The Import Plywood Marketing Group, Inc website says, “Lauan or Meranti was never intended to be used as an underlayment for vinyl flooring.  It was originally designed as a three-ply plywood for paneling.” 

The National Association of Home Builders said, “Typically, ¼-inch luan plywood is used as an underlayment when vinyl is installed over wood subflooring. The problem with luan is that it is soft and susceptible to denting and crushing under concentrated loads such as furniture legs or high heels.

Flooring manufactures agree, and Tarkett said, “A wide variety of species and grades of Lauan plywood have been imported into the United States and sold for use as underlayment. Many of these panels have caused severe problems such as discoloration, delamination and adhesion failures.”

APA, The Engineered Wood Association is a good source of information regarding plywood grades and chances are your supplies distributor carries the “good stuff” so check out what is available.  With so many better products available, why is Lauan still being used? To save a few pennies a square foot.  The fact is, your customer WILL pay more for a stronger warrantee so there is no excuse to use an inferior product.  If that’s not enough, many other resilient manufacturers have similar statements to those I have mentioned, so if you are using lauan, once again “the word warranty may not be in the conversation.”





Proper selection of wood underlayment provides a smooth, hard and guaranteed substrate for resilient floors.



Q: What about installing on plywood over concrete?

A: I get asked this question a lot, especially by architects who need to build up the height of a floor or provide a level of insulation under a resilient floor on concrete.  I don’t recommend installing resilient flooring over plywood installed directly over a concrete slab or over a “sleeper” system (when 2 x 3 or 2 x 4 on a concrete slab with plywood over them).  Wood floors are often installed in these cases but fully adhered resilient should not be.  The problem is that if even a small amount of moisture comes up from the concrete subfloor into the plywood underlayment, the plywood will swell.  Even a slight bit of swelling will lead to telegraphing - the joints and fasteners will show through the new floor. Even with all of these warnings, some jobs go ahead anyway so remember that telegraphing is never covered under a floor covering, adhesive or underlayment manufacturers warranty in such cases so if it happens you are on your own.





This floor was installed in warm weather, and when the air conditioning went on, gaps showed up in several areas of the floor.

Q: What do I do if the concrete isn’t dry enough?

A: This could take an entire column buy itself but here is a quick answer. First, make sure the moisture testing was done correctly. If the testing is not done correctly, the results mean nothing, especially with the ASTM F 1869 (Calcium Chloride) test that measures Moisture Vapor Emission Rate (MVER) as pounds of moisture vapor/1000 square feet/24 hours or just “pounds.” The two most common ways ASTM F 1869 is done wrong are when the HVAC is not on or when the slab isn’t cleaned by grinding before putting the test kit down. That is why the ASTM F 2170 (Relative Humidity probe) test is becoming used more frequently – it is not as sensitive to temperature and humidity in the air and it measures moisture inside of the slab instead of just at the surface.  However, assuming the tests were done correctly and you are very confident of the results, there are three common options when the MVER is too high. 

One, if it’s a new slab you can wait for the slab to dry. Drying can be accelerated by shot blasting to open the slab up, running fans and/or dehumidifiers and/or turning up the heat. Some of the same equipment used to dry out buildings after a flood can be used to dry out a slab.

Two, “use a different floor covering” is a common answer because alternates are  thought to have better resistance to moisture.  For example, carpet or Vinyl Composition Tile instead of sheet flooring. This is a bad idea!  These products and their adhesives can also fail because of excessive MVER and elevated pH.

Most often, there is no time to wait and the flooring choice cannot be changed so some kind of surface applied vapor reduction system will be used. There are dozens on the market so selection can be confusing.  In a nutshell, there are “light duty” products that have a warranty up to a maximum MVER, often 8 to - 10 lbs. These products are risky because they rely only on ASTM F 1869, which measures moisture only at the very top of the slab (less than 1” down) and is often done incorrectly.  Concrete dries from the top down so ASTM F 1869 does not ‘see’ moisture down inside the slab and when that moisture moves upward, which it will, the system can fail.  At that point the slab is tested again and if the MVER is higher than the upper limit for the product, the warranty is void. On the other hand, “Heavy duty” products usually have upper MVER limits of 20-25 lbs, which is actually higher than the test can measure.  These products can take very high moisture levels - some can even go on top of a brand new slab.  The best products are 100% solids epoxy products that are applied over a shotblasted concrete slab in one, two and sometimes three coats, depending on the product.  Some require that sand be broadcast into the top coat and some do not.  Shotblasting is an important part of the process because it removes any contamination and opens the pores of the concrete, both important in order to have the strongest possible bond.  The best “heavy duty” products cost more and require shot blasting, and offer the best level of protection and warranty.



There are many more questions so I am hoping to continue doing these Q&A columns in the future.  Thanks again for your support these past six years and keep those questions coming!