Frequently Asked Questions

What is the difference between the pre-applied Proofex Engage method and the post-applied (pre-applied to formed concrete) waterproofing method for basement slabs?

The pre-applied method (using Proofex Engage or similar membranes) and the post-applied method (applying a waterproof coating or membrane to the outside of an already-constructed basement wall) are both forms of positive-side (ground-side) waterproofing for basement structures, but they are installed at different stages of construction and have different performance and access characteristics. In the pre-applied method, the Proofex Engage membrane is laid on the blinding concrete (or on the formation soil for slabs) before the reinforcement is placed and the structural concrete is poured. The concrete bonds directly to the self-adhesive face of the membrane during casting, creating a structural bond that prevents any water infiltrating through a membrane defect from migrating laterally under the membrane to cause extensive wetting away from the defect location. Post-applied waterproofing is applied to the outer face of the already-formed basement wall after striking the formwork. While post-applied coatings (cementitious waterproof coating, bituminous tanking) are simpler in concept, they require clear external access to the outside face of the basement wall after construction (which is only available before backfilling), and they do not bond structurally to the concrete in the same way — any localised adhesion failure under the post-applied membrane allows water to migrate under the membrane away from the defect. For basement slabs below water table, the pre-applied Proofex Engage method is technically superior because access to the slab underside after construction is impossible, and structural bonding prevents lateral water migration under the membrane.

How are Proofex Engage membrane laps and joints made at the slab-to-wall junction and around service penetrations?

Membrane laps and continuity details are critical in any waterproofing system — a lap or junction failure is the most common cause of basement waterproofing system failure, and all laps and junctions in Proofex Engage must be made with the specific Fosroc accessories designed for the membrane system. At membrane-to-membrane overlapping joints (where two rolls of Proofex Engage overlap on a flat slab), the minimum overlap width is 100 mm, with the self-adhesive surfaces of the two sheets contacted together; the lap joint is firmly pressed and consolidated by roller to ensure full contact and adhesion across the full 100 mm overlap width. At the junction of the horizontal slab membrane with the vertical wall membrane (the kicker or upstand junction), a strip of Proofex Tape (the Fosroc self-adhesive jointing tape for the Proofex system) is used to bridge the angle and seal the junction between the horizontal and vertical sheets before the vertical Proofex Engage is lapped down from the upstand. At internal corners (re-entrant angles), pre-formed corner pieces from the Proofex accessory range are used — never attempting to fold or cut the Proofex Engage sheet around a sharp corner, which risks tearing the HDPE and creating a defect. At pipe and service penetrations through the slab, pre-formed pipe collars or hand-formed seals using compatible Proofex liquid applied membrane are used to maintain continuity of the waterproofing around the penetration.

Can Proofex Engage be used in contaminated ground conditions and what chemical resistance does the HDPE face provide?

The HDPE (high-density polyethylene) outer face of Proofex Engage provides good chemical resistance to the range of soil and groundwater contaminants typically encountered in brownfield development sites and industrial land redevelopment in India. HDPE is resistant to: mineral acids and alkalis at moderate concentrations (soil pH from 2 to 12); chlorinated and aromatic hydrocarbons (diesel, petrol, coal tar, lubricating oil) at the concentrations typically found in contaminated ground; and sulfate-containing groundwater (including the high-sulfate conditions common in some Indian subsoils that cause sulfate attack on concrete). The self-adhesive bituminous compound layer bonded to the inside of the HDPE face provides a secondary barrier against hydrocarbon contaminants that might diffuse through the HDPE layer over time. For highly contaminated sites with concentrated chemical contamination (industrial sites with chlorinated solvents, phenols, or other aggressive organic chemicals at high concentration), the chemical resistance of HDPE and bituminous systems should be verified against the specific contaminant types and concentrations identified in the site investigation report before Proofex Engage is specified. In some highly contaminated situations, a thicker or more chemically resistant membrane may be needed, and Fosroc technical support should be consulted with the contaminant data from the site investigation.