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  • The Proper Time & Place for Acid Washing

    April 13, 2016
  • The most commonly performed surface revitalization technique is acid washing. That’s because acid washing can do wonders to remove stains and other discolorations. That said, acid washing is not an answer for every problem. For example, if the plaster is approaching the end of it’s life expectancy, it may be time to re-plaster rather than further weaken the surface with acid. Furthermore, it should not be used on pools where the plaster has lifted, or blistered, a condition called spalling or delamination, This is considered a cementitious failure, and aggressive water can further deteriorate the surface. Such pools may ultimately require resurfacing. Acid washing is also no solution for calcium nodules, for which there is no chemical treatment, and will also require resurfacing. Acid washing is appropriate for surface stain removal of metals, scale formation and algae. Acid washing is also done on newly set aggregate surfaces, such as pebble or bead-embedded plaster, because it helps to expose some of the aggregate.

    In the service industry it is a fairly commonly offered service. Last year’s Service Industry News survey revealed that in both California and Florida, for example, of those responding to the survey, about 50 percent include acid washing among their offered services. That’s likely because its also fairly lucrative. Service technicians in these areas of the county charge an average of about $600 for the service. Acid washing begins with draining the pool. As always. when draining a pool, great care must be taken to ensure that hydraulic pressure will not result in the pool popping. To protect the pool, open any hydrostatic relief valves or plugs. It is recommended to use a separate pump that is not part of the circulation system to drain residential pools. Take care to monitor the discharge water to protect lawns and shrubs, and to be sure neighboring properties are not flooded. The water must be drained far enough away so as to avoid wash outs or hydrostatic problems.

    When the shallow end is revealed, start the procedure for the acid wash. Begin by cleaning dirt and oils away with a low-sudsing detergent. Acid washing involves using the extremely caustic chemical, hydrochloric  acid, commonly called muriatic acid in the industry.Therefore it’s necessary to protect against injury by wearing the appropriate protective gear, which includes a gas mask respirator, rubber gloves, rubber boots, a suit, and goggles. Muriatic acid is commonly sold in a 20 Baume strength. This is a 32-percent dilution of hydrochloric acid. Further dilutions of 32-percent hydrochloric acid appropiate for acid washing or etching are described as follows:

    For an acid wash, a 3- to 4- percent hydrochloric acid solution is recommended. Always ass acid to water, never the reverse, as an explosion may occur. To obtain 4-percent dilution strength, mix 1 gallon of 32-percent HCI with 4 gallons of water. For an acid etch , a 10-percent hydrochloric acid solution is recommended. To obtain 10-percent dilution strength, mix 2.5 gallons of 32-percent HCI with 2.5 gallons of water. Acid etching is similar to acid washing except that a higher concentration of acid is used. Etching is appropriate for the surface preparation involved in painting or re-plastering.

    These acidity strengths are general guidelines and specific circumstances will call for different acid strengths. It may be necessary to adjust the dilution when treating a painted pool or various densities in the masonry finish. It’s a good idea to mix the recommended dilution and then scale up or down as the situation calls for it. To get started, wearing personal protective equipment, prepare the solution and then begin applying the solution with a plastic sprayer. Work in sections and do not attempt to apply the acid to the entire pool at once. Badly stained areas should be scrubbed with a non-metal brush and hose rinsed when the foaming has stopped or if the area is sufficiently cleaned. Do not allow acid to dry on the plaster because it will damage the surface. Not all stains can be removed with an acid wash although some stains may require multiple applications to come out.

    Experts agree that it is better to apply multiple doses of a weaker dilution than accidentally using too strong of a solution.When the wash is complete, a soda ash solution is used to neutralize the active acid on the plaster surfaces. It also neutralizes the waste water that has accumulated to the EPA acceptable pH level of 6.0 to 8.0. It’s preferable to neutralize to a pH level of 7.0. Before refilling the pool, rinse all surfaces with fresh water and dispose of the waste water as per local regulations. After acid treatment is complete, be sure to flush out the plumbing to prevent corrosion. The pool may then be refilled by placing the hose carefully in the deep and, unless further treatment, such as painting, Service Industry News s

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