Mainstay ML-Flex is a cementitious, acrylic based, flexible waterproofing membrane and coating. This product is suitable for permanent water immersion service. ML-Flex is used primarily to waterproof concrete structures above and below grade and as a lining inside in aquariums, zoos, fountains, water features, planters, and reservoirs. It is considered a low cost alternative that may be used in "back of house" applications or beneath theming (e.g. artificial rockwork and coral) where appearance and cleanability are of secondary importance. Mainstay ML-Flex will bridge static hairline cracks, but has limited ability to bridge cracks which move over time.


Mainstay ML-Flex product data PDFDownload our product detail sheet (33 KB, opens in separate window).

Mainstay ML-Flex over concrete substrateBenefits of Mainstay ML-Flex Cementitious Waterproofing Membrane:

  • seals rough, deteriorated surfaces
  • resists negative side and positive side hydrostatic water pressure
  • produces excellent adhesion to properly prepared substrates

Product Overview


This is a two component product. Component A is a mixture of cement, silica fillers, and admixtures. Component B is a proprietary acrylic solution.


Normally stocked as a kit consisting of one 50 pound bag and one 20 pound bucket


Per 70 pound kit (allowances should be made for waste):

Approximately 114 square feet at 60 mils

Approximately 85 square feet at 80 mils

Approximately 76 square feet at 90 mils


Mix entire contents of bag component A and liquid component B in a five gallon bucket


Standard gray and off-white; custom colors available upon request

Working TIme

Approximately 30 minutes at 80° Fahrenheit

Application Equipment

Contact us for information regarding the proper equipment to apply this product.