Polymer-Modified Flexible Cementitious Waterproofing

Cem-Kote Flex ST

Two-component, fibre-reinforced, breathable cementitious waterproofing for positive- and negative-side concrete protection.

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Technical basis CEM-KOTE FLEX ST
  • Approved to ANSI/NSF Standard 61 for potable-water barrier materials in Industrial Gray.
  • Bridges substrate cracks up to 1.6 mm when reinforced and provides positive- and negative-side waterproofing.
  • Suitable for tanks, tunnels, balconies, patios, slabs, and open wastewater structures requiring flexible waterproofing.

Decision Summary

When to specify Cem-Kote Flex ST

  • The substrate has existing cracks or expected movement.
  • Water pressure or frequent wetting is part of the service condition.
  • The project needs a mineral membrane accepted for potable-water contact.

Core Uses

Flexible waterproofing, crack bridging, and water-retaining structures

Flexible Cementitious Membrane

CEM-KOTE FLEX ST is a breathable membrane that can accommodate substrate movement while maintaining cementitious compatibility with concrete and masonry. It is specified when rigid waterproofing is too brittle for expected crack movement.

Crack Bridging and Reinforcement

Cracks are treated with CEM-KOTE FLEX ST and REINFORCING FABRIC NW or REINFORCING FABRIC HD. Below-grade work typically calls for REINFORCING FABRIC HD, while elevated slab crack treatment may use NW according to the guide specification.

Water-Retaining and Exposed Structures

The product is used on tanks, tunnels, balconies, patios, slabs, and open wastewater structures where positive/negative waterproofing, UV resistance, freeze-thaw resistance, and vapor permeability matter together.

Comparison Block

How the material changes the specification

Rigid Mineral Coatings: Common Limitations

  • Can crack when the substrate continues to move after waterproofing.
  • May force the designer to choose between vapor permeability and crack accommodation.
  • Often require separate detailing at cracks, corners, and transitions to avoid leakage paths.

CEM-KOTE FLEX ST: Practical Value

  • Provides flexible waterproofing while remaining breathable and cementitious.
  • Allows reinforced crack detailing with fabric embedded into the membrane.
  • Fits potable-water, water-retaining, below-grade, balcony, and restoration applications.

Technical Data Table

Reported product data and test references

PropertyValueSource / test
System typeTwo-component flexible fibre-reinforced cementitious slurryOfficial product description
Coverage100 ft2 / 16.25 m2 per kit at 64 mils totalTwo 32 mil coats
Crack spanning0.5 mm non-reinforced; 1.6 mm reinforcedW. R. MEADOWS TP 005
Water vapor permeance697 ng/Pa.s.m2 / 12.8 permsASTM E96 wet cup at 1.6 mm
Negative-side impermeabilityWater head >126 ft / >38.4 m at 2 mmTTP 1411
Pot life40 minutes at 68 F / 20 C, 60% RHProduct data sheet

Application / Specification Notes

Preparation, installation, curing, and limitations

Substrate Assessment

Confirm substrate soundness, contamination, moisture condition, cracks, exposed reinforcement, and service exposure before selecting the final Gemite system.

Application Planning

Follow the current product data sheet and guide specification for mixing, surface preparation, application thickness, curing, and environmental limits.

Permanent System Build-Up

Where the product is used as a repair or first-response material, complete the sequence with the compatible waterproofing, repair, or protection layers required by the project.

System Compatibility / Related Product Notes

Related Gemite system interfaces

FIBRE-PRIME

Use on exposed reinforcement where corrosion protection is required before repair mortar placement.

FIBRE-PATCH GP / OV

Use repair mortars to rebuild damaged concrete before final waterproofing or coating layers.

CEM-KOTE Systems

Select Cem-Kote waterproofing or protection products according to water pressure, movement, chemical exposure, traffic, and potable-water requirements.

FAQ

Specification questions

Should the substrate be wet or dry before application?

It should normally be saturated surface dry: damp enough to avoid suction, but without standing water that would dilute or disturb the coating.

When is reinforcing fabric needed?

It is commonly used over existing cracks, corners, penetrations, and underground or higher-risk areas where movement or stress concentration is expected.

How does it differ from CW Plus?

Flex ST is a flexible surface membrane with crack-bridging capacity. CW Plus is crystalline waterproofing that reacts inside the concrete matrix.

When is reinforcing fabric required?

Existing cracks, below-grade detailing, corners, and high-risk movement areas may require reinforcing fabric. Below-grade applications typically use REINFORCING FABRIC HD; elevated slab crack treatment may use REINFORCING FABRIC NW.

Can it remain exposed?

Flex ST is UV resistant and suitable for many exposed cementitious waterproofing applications, but final exposure, traffic, color, and coating requirements should be confirmed against the current data sheet and project conditions.

Next Step

Need technical guidance for this system?

Send the substrate condition, exposure, traffic, crack profile, and coating sequence. Gemite can help confirm whether this product fits the project conditions.

Request Technical Guidance

Or contact us: office@gemite.tech · +40 232 273 031