Repair Systems — Basement Water Ingress
Positive & negative side tanking coatings
Technical product reference for two-component cementitious tanking coatings applied to positive (water-facing) and negative (dry-side) substrates in basement and below-grade waterproofing remediation — for structures subject to hydrostatic pressure where membrane systems cannot be applied to the water-facing side.
What are positive / negative tanking coatings?
Positive / negative tanking coatings are cementitious (often latex-modified) slurry coatings applied to below-grade concrete and masonry to form a water barrier. "Positive side" means the coating is on the water-facing (external) face — the preferred configuration; "negative side" means it is on the dry interior face, used where the external face is inaccessible. Negative-side coatings must resist hydrostatic pressure trying to push them off the substrate, so the manufacturer's pressure rating must be confirmed.
They are applied to a clean, prepared substrate after any active running water has been stopped with a hydraulic cement plug, and are not suitable for structures with significant ongoing movement. Confirm the side of application, the negative-side pressure rating, primer and surface preparation from the manufacturer TDS.
Product Reference
Individual products — one card each — scroll to view all
Westox
Westox CR25
Latex-modified cementitious tanking coating — positive / negative side
Westox CR25 is a latex (acrylic) emulsion used with GP cement as a tanking membrane for internal and external walls and to provide a sealed surface on concrete under a sheet membrane — usable for both positive- and negative-side waterproofing. It also bonds render to high-strength / non-porous concrete and eliminates render slide. Mix 1 part CR25 to 2 parts GP cement by volume; 5 L CR25 + 10 L cement gives ≈12.5 m² at 1 mm. Available in 5 L and 20 L. Stop active water (hydraulic plug) first; confirm the negative-side hydrostatic rating and the render sequence from the Westox CR25 TDS.
System Comparison
Positive / negative tanking coatings — confirm all selections against the current manufacturer TDS before specifying.
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Disclaimer
This page provides general technical information only. Final product selection must be confirmed against the current manufacturer technical data sheet, project specification, substrate condition, and structural engineer advice where applicable. Basement and below-ground waterproofing involves hydrostatic pressure — confirm system selection with a qualified waterproofing consultant before specifying. Do not rely on this reference as a substitute for professional advice.