Frequently Asked Questions

How is Nitofoam 40 installed at a construction joint in a basement wall and when should it be fixed?

Nitofoam 40 installation at a basement wall construction joint follows a simple procedure. After the first pour of concrete (for example, the lower portion of a basement wall) has cured and the formwork has been struck, the top face of the hardened concrete at the joint location is cleaned of laitance, dust, and loose material. The Nitofoam 40 foam strip is then adhesive-fixed (using the compatible contact adhesive or the self-adhesive backing on the foam) to the cleaned concrete face at the intended joint location — typically centred on the wall thickness or positioned at a specific depth as shown in the waterproofing specification. The strip must be fixed continuously without gaps along the full length of the joint (including around corners and intersections) and pressed firmly into contact with the concrete surface. The second pour of concrete is then cast over and against the Nitofoam 40 strip, enclosing the foam within the joint. When groundwater reaches the joint, the foam swells and seals the joint against water passage. The timing of installation is immediately before the second pour — the foam must not be exposed to rain or standing water before the second pour is cast, as premature swelling in the unconfined state reduces the effectiveness of the seal in the confined joint.

What happens to the Nitofoam 40 waterstop if the construction joint remains dry for an extended period after concreting?

Nitofoam 40 only swells and activates when it is exposed to water. If the construction joint remains permanently dry (for example, in a building above the water table, or in an area where groundwater is permanently controlled by drainage), the foam strip remains in its unswollen dry state within the joint indefinitely without degrading or losing its potential to swell if water subsequently reaches the joint. This is an advantage of hydrophilic foam waterstops over some other sealing approaches — they are passive systems that activate only when needed. If water subsequently enters the joint (for example, if drainage around the basement fails, or if the groundwater table rises seasonally), the foam swells and seals the joint. The swelling is reversible to a degree — if the joint dries out again, the foam may partially shrink back. In conditions of intermittent wetting and drying, the repeated swelling cycles can reduce the swelling performance over time — permanent wet conditions are the optimal service environment for hydrophilic foam waterstops.

Can Nitofoam 40 be used for the construction joint at the base of a basement wall at its junction with the raft foundation slab?

Yes. The construction joint at the wall-to-raft junction is one of the most critical waterproofing joints in a below-ground structure — it is at or below the water table in many projects, it is a long joint running the full perimeter of the basement, and it is subject to significant hydrostatic head from groundwater. Nitofoam 40 is an appropriate waterstop for this joint. The installation procedure is: after the raft slab is cured, clean the top surface of the raft at the wall starter bar zone where the wall construction joint will form; fix the Nitofoam 40 strip continuously around the full perimeter on top of the raft at the wall formation line; and cast the basement wall concrete against and over the foam strip. At the corners and at construction break points along the raft perimeter, the foam strips must be overlapped and butt-jointed with adhesive to maintain continuity of the waterproofing seal. The raft-to-wall joint should be designed as part of the complete basement waterproofing system specification, which will typically include the Nitofoam 40 construction joint waterstop combined with the external Fosroc Proofex membrane system on the outside of the basement structure.