With the Concrete Vapor Movement Comes the Alkali Salts

With the Concrete Vapor Movement Comes the Alkali Salts

With water vapor moving upward into the slab comes the alkalinity degrading to adhesives causing the flooring material to lift from the concrete surface.  As the vapor moves through the slab capillaries, alkali attaches itself and is then deposited on the slab surface. The failures are two fold as we can see the bumps from the accumulation of the moisture telegraphing through vinyl sheeting and tiles, combined with the lack of bond to the concrete surface as the adhesive is damaged by the alkali.

The alkali is the white substance we’ve all seen in concrete cracks or lying on the concrete surface, oozing up between commercial vinyl or rubber tile or the old asphalt 9” x 9” tiles installed prior to the 1970’s. The white alkali powder is the damaging material to adhesives with pH of 12 and above. pH above 10 is considered damaging to flooring.

What is pH? pH stands for Potential of Hydrogen and is a measure of acidity or alkalinity of a solution on a measured scale of 0 to 14. A pH of 7 is neutral, pH measurements above 7 are alkaline and below 7, acidic.
Concrete is Alkaline based because cement is alkaline with pH of above 13 and very caustic. To test this fact place your hand in wet concrete for a few minutes and you will soon feel the burn.

NOTE:: Fascinating statement found on Wikipidia:

“pH is normally measured in a range of 0-14. However, due to the way pH is calculated, it’s possible to have negative pH and pH above 14. However, it should be noted that reported values outside the range 0-14 are somewhat controversial; as measuring pH beyond this range becomes difficult.Runoff from mines/mine tailings can produce some of the most acidic pHs ever reported; with negative pHs measured and reported in the literature as low as pH -3.6”.

Good quality concrete will have a pH of 12 to 12.5 within the slab itself while the surface can be 10, or even less.
High density concrete minimizes the upward movement of hydroxides of sodium, potassium and calcium released during the various hydration reactions. Alkali movement is hindered in high strength, low permeability concrete slabs but the real world dictates placement of concrete by low bidders in all weathers using unskilled labor.


Concrete Moisture Testing Inspectors-Technicians