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The Case of the Owner Who Had His Own Way
By Eric Kline - KTA-Tator, Inc.
A municipality located in the northeastern United States owned and operated a community swimming pool. The steel in-ground pool was protected by consumable magnesium anodes attached to the pool sides. After many years, the owner decided to blast clean and repaint the pool. The contractor was to blast clean the pool in accordance with SSPC-SP10 "Near White Blast Cleaning." The pool was to receive two coats of an immersion-grade polyamide epoxy paint. The municipality elected to have the blast cleaning done by a local painting contractor, but opted to have the coating applied by its own crew. The "crew" consisted of seasonal employees hired by the municipality.
After blast cleaning, the seasonal workers coated the pool bottom and sides with the specified materials. Application was done using rollers (the municipality did not have spray equipment, and doubted that the seasonal workers knew how to operate such apparatus). After the spring coating application, the pool was filled with water and opened to the public.
During the swimming season, many complaints were lodged with the pool manager. The complaints were of two types: The pool bottom and sides were rusting in streaks (but not on lane marker strips), and the bathers' suits (especially dark ones) were stained by the paint.
At the conclusion of the season after the pool was drained, liquid-filled blisters were noted. Because of these problems, KTA was contacted to perform an independent evaluation of the pool coating.
In the Field
The KTA consultant visited the pool site and evaluated the field circumstances surrounding the project. Samples were collected for laboratory analysis, including blister caps and blister liquid. Further, photographic documentation was obtained.
In the KTA Laboratory
The blister liquid was analyzed in the laboratory using gas chromatography and Fourier Transform Infrared Spectroscopy. The analysis revealed that the blisters contained water and solvent. The solvent was found to be a ketone material. The ketone solvent was not a component of the paint, but was identical to the thinner found by the seasonal crew in the maintenance storage shed and added to the paint. The white material deposited on the bathers' suits was found to be calcium carbonate.
Field observations, combined with laboratory analysis, suggested the following:
- Blistering was caused by solvent entrapment due to inadequate curing of the coating prior to immersion. The ketone solvent was added to the paint as thinner by the paint crew.
- The stains on the bathers' suits were the result of chalking of the paint and were composed of calcium carbonate filler in the paint. Polyamide epoxy paints are prone to chalking due to the effect of sunlight on the paint binder.
- Rusting occurred in roller-shaped strips due to inadequate thickness during application. Rusting was not present on lane-striped areas, because of the application of an extra coating layer in these areas. This extra thickness covered the blast profile.
The use of an applicator-sensitive polyamide epoxy pool coating by an inexperienced seasonal crew is an invitation to this type of failure. Product adulteration by using the wrong thinner and applying the coating too thin are not unexpected results in such cases.
Blistering due to the osmotic effects from retained solvent may have been the result of the incorrect thinner or inadequate cure time prior to immersion. Because of spring wet weather patterns in the northeastern United States, it is difficult to blast clean and paint in the spring and still have pools open on Memorial Day. For that reason, owners should consider painting pools in the fall when weather patterns are generally more favorable.
Chalking is an inherent characteristic of exposing polyamide epoxy materials to sunlight. For this reason, owners often select acrylic or vinyl-type materials for such service.
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