Many floor-covering failures are thought to be moisture related when the real problem has more to do with salt. It’s called “alkaline efflorescence” and it helps explain why a floor with an acceptable moisture reading can fail anyway. Say, for example, your test for moisture emissions on VCT tile job reads 4 pounds and the manufacturer’s recommendation is 5 pounds. If the job goes sour some would simply assume the moisture emissions must have somehow increased. Not true. Further testing will indicate that the moisture level is still below the 5 pound level. A pH test, however, will reveal that the real culprit is alkaline efflorescence. It is a crystalline residue of an evaporated salt solution from the lime in Portland cement.
Figuring this our gets a little complicated, but this is why people seek out certified professional installers. It comes down to chemistry. There are basically three by-products of Portland cement that create alkalis: sodium oxide (Na2O) pH 14.0, potassium oxide (K2O) pH 13.0 and calcium oxide (Ca (OH) 2 pH 12.5. When mixed with moisture that is migrating, the water will convert sodium oxide into sodium hydroxide (NaOH), or a caustic soda. The hydroxide then migrates to the surface of the slab where it evaporates leaving an unwelcome alkali deposit. Another form of efflorescence is sodium carbonate, which is sodium hydroxide mixed with carbon dioxide from temporary heat. This is also refereed to as soda ash.
Potassium oxide is dissolved by water to form potassium hydroxide (KOH), or lye. Potassium hydroxides will migrate to the surface of the slab to create another form of efflorescence. This type of hydroxide can also mix with carbon dioxide from temporary heat to form potassium carbonate, also known as potash.
The hydration of Portland cement can be another source of alkaline efflorescence. Excess water added the Portland cement in concrete forms calcium hydroxide (Ca(OH)2. Water migrating can dissolve the hydroxide and carry it in a solution to the surface of the slab. When the water evaporates it leaves a white crystalline residue, also known as hydrated lime. Temporary heat, especially from sources that produce high amounts of carbon dioxide, mixes with the sodium hydroxide, potassium and /or calcium hydroxide. This creates either sodium carbonate, potassium carbonate, calcium carbonate or all three. Bottomline: each one can screw up your floor covering adhesives. Adhesives will either crystallize and turn to powder or disappear:
A few important points to keep in mind about the effect of pH on flooring:
• When alkali salts reach the surface of the concrete and start to dry they tend to expand exerting a pressure in excess of 3 tons on the adhesive’s bond to the concrete.
• When concrete is poured from a cement truck the pH is about 12 - 13.
• If you were to dig down into concrete and do a pH test you will get a pH reading of around 12.
• A pH of 13 will dissolve glass.
• A pH of 13-14 will start to decompose some certain types of sand and aggregate in the concrete mix.
Testing for alkalinity
Only recently has the flooring industry come to understand that moisture vapor migration is not always the blame for a flooring failure. Moisture is merely the vehicle that carries the destructive alkaline salts to the surface of the slab. This explains why we are starting to see more pH test kits along side the anhydrous calcium chloride test kits. Yes it is an added burden to do all this testing but the moisture vapor emissions test is not enough. The added tests give a more complete analysis of the concrete’s condition. You need to know for sure if the slab is suitability for the flooring materials your crew is about to lay down. The best time to do these tests is immediately upon retrieval of the moisture emissions test. The concrete was cleaned prior to the setting of the test and the concrete’s surface will tell the amount of alkaline salts that have been brought to the surface by the migrating moisture.
The test is one you may remember from a high school science class. With the concrete already clean, pour about a teaspoon of distilled or de-ionized water on the surface. Let it set on the concrete for about one minute. Then, test it with a strip of with litmus paper. The paper will change color on contact with an alkali. Compare the color changes with a pH color chart to determine the results. (As an alternative, you can use a pH tester. Instead of using paper, a surface probe is placed into the distilled water solution. This method may be more costly but is will give you greater accuracy and more consistency.)
Analysis of the pH test results
Now what? Using a numeric scale from 7 to 14, the test results will tell you the degree of alkalinity on the slab. It is sometimes confusing because it is measured using a logarithmic scale. Each value is ten times greater than the previous number. If seven is neutral, eight is 10 times greater than neutral, nine is 100 times greater than neutral and so on all the way to 14 (10 million times greater than neutral). The magic number is nine. That is the pH level at which alkaline salts start to impact flooring. When it reaches 10, it almost always destroys the adhesive. Because of the caustic nature of the hydroxides, very few adhesives can survive a pH of 10 or greater.
I realize there are few installers who thought they would ever need a white lab coat to go along with the knee pads and trowels, but knowing the ins and out of pH content can save you major headaches. In addition to floor covering materials, adhesives and techniques, installers should have a working knowledge of chemistry that effects their work. The changing world of floor covering is dictating it.