It is unclear whether the torching process affects the long-term durability of a plaster surface, but there are studies that indicate some damage is done to cement products. Sometimes, “torching” (heating) the gray area with a propane torch device is performed in an attempt to remove the gray color. If an acid treatment is used to lighten gray mottling, how is it that slightly aggressive water caused white plaster to darken and turn gray, and in a blotchy, streaky, or spotting fashion in the first place? If the gray discoloration isn’t removed by the acidic process it will then become difficult proving that it wasn’t aggressive water that caused the gray discoloration in the first place and the pool plasterer may be able to avoid being held responsible. But the most unfortunate issue is that the plaster surface WILL BE ETCHED after the acid treatment process is performed, which ages the plaster surface and allows for staining to occur much easier and sooner. While this treatment may occasionally lighten gray discolorations, it often doesn’t work, or the gray color returns within weeks afterwards. Acidic water treatments are an undesirable and improper suggestion for the service tech or pool owner to perform on a new plaster job. In an attempt to remove the smooth gray discoloration, it is sometimes suggested to perform a “zero alkalinity process” or an acid treatment on the plaster. Sadly, these incorrect claims enable some pool plasterers to avoid responsibility for improper practices, and place blame onto innocent pool owners or service techs. There is no research study that supports their theory. Some plastering people incorrectly claim that aggressive water, high cyanuric acid levels, or improper water chemistry startups causes the graying discoloration. Research by independent cement laboratories have documented that white spotting and streaking is not the result of an aggressive water (etched caused) condition, but is caused by improper workmanship practices and troweling techniques (such as adding lots of water while troweling) which results in localize areas of greater porosity (lighter soft areas or spots) on the plaster surface.

Gray mottling of new plaster pools is sometimes accompanied with “white soft spots” or streaking (also incorrectly called “spot etching” or “etching deterioration” by plasterers). The addition of calcium chloride to a plaster mix is also known to cause graying of cement, in addition to making the plaster less durable over time. A very low water-to-cement ratio almost always leaves a darker finish color. Late hard troweling can cause a darkening of the color of white cement because it decreases the water-to-cement ratio of the plaster surface. This graying discoloration is difficult to remove, and is often termed as a “hydration problem” or “entrapped moisture.” This type of dark discoloration should not be confused with metal or calcium scale staining. Usually, this type of staining can be easily and safely removed from the surface by acid washing, sanding, using sequestering or chelating chemicals, or other stain removal products.įor this article, we are discussing a blotchy or streaky, and very smooth gray discoloration that sometimes develops during the first few months after plastering and being filled with water. (Concrete Slab Surface Defects: Causes, Prevention, Repair Portland Cement Association 2001).Īlthough some discolorations are the result of metals precipitating and depositing various color residues onto the plaster surface, these are referred to as surface staining. It is also called “pinto concrete” in the cement industry. Trowel “burn” is another cause of extreme dark discolorations of white plaster. Gray (also spelled “grey”) or darkened blotchy or streaky discoloration of pool plaster (cement flatwork) is known to be caused by several improper plastering practices, including the addition of calcium chloride to the mix (even less than 2%), late hard or dry troweling, and sometimes a cement material issue can lead to this problem.

Grey pool plaster repair