Acid Washing Fresh Pool Plaster Can Be A Recipe For Disaster

Acid washing freshly placed plaster is one of the most destructive things you can possibly do to the surface of a swimming pool.  Meaning that the difference between a pH of 13 and a pH of 0 is 1,000,000,000,000. Yes, you read that right, one trillion.  In this white paper that I wrote with Jon Temple of Tempool Inc. we’ll explore why acid washing fresh pool plaster can be so disastrous.

The Acidity of Concrete

Freshly placed concrete has a high pH of 12.5-13. The high pH originates from the alkaline cement binder that creates concrete. The dissolved cement spreads this high pH throughout the matrix of the concrete. The same chemistry occurs within cement-based pool plaster.

Fresh concrete’s high pH makes it more volatile in response to chemical exposure. It is so sensitive to acidic conditions, that it even reacts with the carbon dioxide in the air, a process called carbonation. This process will eventually affect the concrete at deeper levels.

Washing virgin plaster or cement surfaces with an acid solution of 0, will be extremely detrimental to the lifespan of the concrete. The thinner veneer of plaster is even more susceptible to long-term damage by acid exposure.

Chemical Reactions To Lead To Degradation

When the pH of concrete drops below 9, the chemical nature of the cement has been altered so much that it begins to lose its ability to bind. This is most evident on the surface of the concrete, as it begins to chalk, flake, spall or release aggregates (etching). As these layers decay, they further expose the underlying layers to degradation.

To expose aggregates, a high pH solution should be utilized to minimize the damage to the cement. Even a rinse solution with a pH of 7.5 is better than one of 0, since the pH scale is logarithmic – that is each 1.0 change on the scale is a 10 fold change in the intensity. A final rinse with a pH solution of 13, will restore the surface of the cement to its natural pH state of 13.

Exposing and rinsing the cement surface with solutions that are closer to the 13 pH of cement will ensure that the plaster company does not prematurely damage or etch the cement surface.

Swimming Pool Expert Witness