Pool Mottling

Pool Mottling

Posted by DG Pool Supply on May 17th 2024


Mottling (AKA Hydration / Trapped Moisture)

The pool does have a “Mottled” appearance as described by both the National Spa and Pool Institute’s Guideline (NSPI) and the National Plasters Council Guideline (NPC). These guides state that pool finishes “shall be uniform in shade of color, subject to normal cement plaster mottling and shading”. The guides further state that “plaster is a hand troweled, cement product. Variations in shading (including shadowing, streaking and discoloration) are a normal occurrence and not considered a deficiency”. We are certain that there is no defect in the material as we have conducted tests on samples from other mottled pools and never found contaminate. Mottling is a natural phenomenon that occurs in all pool plaster to some extent. It is affected by environmental factors such as sunlight, heat, wind, water content, water temperature and humidity which are not within the plasterer’s control. At this time, there is no consensus on the cause or cure of mottling, but I will keep you informed of any findings on the subject.

Possible Causes of Mottling They are usually blotchy Gray or black areas on the surface of the pool. Hydration Problem is commonly known as Mottling / Trapped Moisture. It can appear as soon as the first day of the job or can take as long as 4-5 months to appear. Unbalanced water during start-up. High PH & Total Alkalinity during the Hydration process (28 days). Can cause Scale over the finish and seals in remaining moisture. Areas in shell preparation that were plastered over. Varied areas of thickness in application widely over or under recommended specifications. This is known as green areas



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