PH Testing: Is it really necessary?
July 1, 2006
The answer is NO... if you have a lot of time and money. If you have both of those commodities in excess you may not need to read any further, but having been involved in the flooring industry for 37 years I never seemed to accumulate an excess of either one, so if you're like me you will want to read on.
We will address several topics:
- What is pH?
- What is the difference between pH and a concentration of alkalinity?
- How to properly test for pH.
- How to tell if the tests are accurate.
- What effect pH has on floor covering installations?
- How to control pH.
Simply stated pH is the strength of the acidic or alkaline elements of a given material. It all has to do with the hydrogen and hydroxyl ions that co-exist in water. More hydrogen ions and the solution is acidic, more hydroxyl ions and it is alkaline. The strength is expressed in a number scale from 1-14, 1-6.9 is acidic, 7 is neutral, 7.1-14 is alkaline. The scale is logarithmic, every increase or decrease in a full number is a ten fold increase or decrease in strength, so 10 is 10 times stronger than 9, 11 is 100 times stronger than 9 and so on.
All healthy concrete is alkaline by nature with a pH of 12-13. As it cures, dries, carbonates and ages it begins to neutralize the alkaline elements at the surface of the concrete. Eventually the pH will stabilize at about 9, but this takes time and in most cases time is something we don't have.
As for the concentration of alkalinity, think of it this way, pH is the strength, and the concentration of alkalinity is the intensity of the alkaline elements in the concrete (hydroxides). pH is the sprinter, he can go fast but for only a short time while a concentration of alkalinity is the marathon runner, he just keeps on going, and going, and going. pH at the surface can be leeched away or neutralized naturally but if there is a concentration of alkalinity that surface pH will renew itself and problems can follow.
Since most floor covering manufacturers have limits on what they will accept in regard to the pH of the concrete their product will be applied to testing it is in the best interests of all, except, those mentioned earlier who have time and money to burn.
Accurate pH testing is essential and something we don't see done often enough. If you read a test report for moisture vapor emission rates and it has a pH test result of anything below 9, and we see too many reports below this value, you can be reasonably sure that these tests were not done correctly. The lowest pH for normal healthy concrete is a pH value of 8.3. Most testing companies don't use hyper sensitive litmus paper or pH meters, so their readings will be full digits 7, 8, 9, 10, so if the report reads 8 or lower the testing was probably not done correctly or you have a severe problem with the concrete. In either case a second look at the testing is warranted.
ASTM F 710 Standard Practice for Preparing Concrete Floors to Receive Resilient Flooring outlines the proper testing protocol for both calcium chloride testing (paragraph 5.2) and pH or alkalinity testing (paragraph 5.3-5.3.1) and both testing procedures are tied to Section 5 paragraph 5.1 dealing with Testing Procedures. Reference is also made to another ASTM standard in regard to proper testing procedure, D 4259 Standard Practice for Abrading Concrete; now here is where the mistakes are made that give us inaccurate pH and vapor emission test results. It states that acceptable methods for preparing the concrete surface are all aggressive enough to break the steel trowel finish, abrasive blasting, mechanical abrading etc. The intent being to remove sufficient material so that the surface is free of glaze, efflorescence, curing compounds, release agents, anything that might form a barrier isolating the concrete.
A quick test to see if the concrete is ready to test is to put a drop of water the size of a nickel on the floor surface, if the surface tension of the water isn't broken and the sides of the water drop don't begin to spread and absorb into the concrete within 60 seconds or so there is something on the surface preventing contact with the concrete. This must be removed to accurately test.
So now we know a little about pH, how to test properly and how to recognize accurate test results, so why should we go to the trouble?
It's cheap insurance; all too often we are called to investigate a flooring problem that looks like these. Remember it's only time and money.
These are all pictures of failures that were not moisture driven but as these photos show the problems that can result when you have elevated pH levels at the surface of the concrete coupled with even moderate vapor emission rates.
The alkaline elements in the concrete were brought to the surface of the floor by water vapor condensing at the concrete-adhesive-flooring interface, this pure water is attracted to the salts in the concrete and is drawn back into the capillaries of the concrete as a liquid, it dissolves the hydroxides lining the capillaries and brings them to the surface were they begin to attack the adhesive. The result is either a separation of the plastisizers from the solids of the adhesive, that stringy mess under the flooring that used to be adhesive, or a chemical attack that destroys the adhesive leaving little but discoloration were the adhesive used to be. In either case the result is time and money, usually yours.
That's all the bad news, and too many of you already have experienced this, so how do you control something that is a natural element within the concrete without compromising the integrity of the concrete?
Some manufacturers suggest rinsing the surface with water to reduce the surface pH, while in theory this sounds good, you need to remember you are making water available to a hygroscopic material (loves water) and we are trying to dry it so we can proceed with the flooring installation. The introduction of water at this time may be counter-productive if time is limited.
Rinsing with a slightly acidic solution to neutralize the pH is another suggestion. However the problem with this is the residue left behind may interfere with the performance of the adhesives.
The other factor to consider is that these methods may work, if we are talking about surface pH or residual efflorescence. If there is a concentration of alkalinity in the concrete it will be only a short time and elevated pH readings will return.
There are penetrating compounds that will react with the soluble hydroxides in the concrete to encapsulate them. These salts can no longer contribute to elevated pH readings at the concretes surface. Now at this point adhesives and floor covering become more tolerant of elevated moisture readings and failures, even though moisture readings are above manufacturers limits, are less likely to occur.
There are also ways to design and place concrete that will help accelerate the drying process and lower the concentration of alkalinity available within the concrete, however we will need to discuss this at a later time.