Frequently Asked Questions

What is the difference between Fosroc Supercast SW (bentonite) and Supercast RX (hydrophilic rubber) and which should be specified for a basement construction joint?

The choice between Supercast SW and Supercast RX for construction joint waterproofing depends primarily on the site conditions and the specific concerns of the engineer and contractor. Both products achieve a water seal at the construction joint through a swelling mechanism — Supercast SW through sodium bentonite clay hydration (very high swell volume, up to 10 to 15 times dry volume), and Supercast RX through hydrophilic rubber expansion (controlled, lower swell volume, typically 2 to 4 times dry volume). For most below-ground basement construction joints in standard residential and commercial buildings in India where the water table is relatively stable and the joint will remain permanently wet once the structure is waterproofed and backfilled, Supercast SW (bentonite) provides an economical and reliable seal. Supercast RX is preferred in the following situations: where the construction joint will experience wet and dry cycles before the structure is backfilled and permanently wetted (during the construction programme, bentonite that swells and then dries and cracks in dry weather loses some sealing performance that the hydrophilic rubber avoids); where the site is exposed to rain during construction and pre-swelling of the waterstop is a risk before the second concrete pour (hydrophilic rubber, having a rubber matrix, is more tolerant of partial pre-wetting); and where a higher-quality product is specified for critical infrastructure (metro tunnels, water treatment) where the controlled swelling and consistent performance of the hydrophilic rubber is preferred by the engineer.

How is Fosroc Supercast RX installed in a construction joint between a basement raft and the first lift of basement walls?

Installation of Supercast RX in a raft-to-wall construction joint follows a straightforward procedure that is integrated into the standard concrete construction sequence. After the basement raft slab concrete has been cast and has cured sufficiently to walk on (typically 24 to 48 hours at 25 degrees Celsius), the kicker formwork for the first lift of basement walls is set up on the raft slab surface. Before fixing the formwork, the Supercast RX waterstop is positioned on the raft slab surface at the centre of the wall width, laid along the full length of the perimeter wall, with the top face of the waterstop at the level that will be centrally embedded when the wall concrete is poured over it. The Supercast RX strip is fixed to the slab surface using concrete nails driven through the strip at 250 to 300 mm centres, or using a compatible waterstop adhesive applied to the bottom face of the strip before pressing it onto the slab surface. At corners and at joints between lengths of waterstop, a minimum 50 mm lap is provided and the lapped ends are bonded with Supercast RX adhesive and firmly pressed together to ensure continuity of the waterstop across the full joint length. The wall formwork is then constructed around the fixed waterstop, and the wall concrete is cast over the kicker and around the upper half of the waterstop profile. After both raft and wall concretes have hardened, the Supercast RX is centrally embedded within the construction joint and activates when water contacts the joint during service.

Can Supercast RX be used in a construction joint of a swimming pool that will undergo regular emptying and refilling through the service life?

Yes — Fosroc Supercast RX is well-suited for swimming pool construction joints precisely because of its controlled swelling and drying-recovery performance characteristics. Swimming pools are emptied for cleaning, maintenance, and re-plastering on a regular basis throughout their service life — typically at least annually and sometimes several times per year for high-use commercial pools. At each emptying and refilling cycle, the water level in the pool passes through the construction joint zone, and the waterstop at the joint transitions between wet (when the pool is filled) and dry or partially dry (when the pool is empty and drying out). A pure sodium bentonite waterstop (Supercast SW) in this application can progressively lose performance over repeated drying cycles because the clay matrix can develop fine desiccation cracks during the dry phase — the bentonite re-hydrates and re-swells when the pool is refilled, but over many wet-dry cycles the clay structure can become less cohesive and the sealing pressure in the dry phase is reduced. The hydrophilic rubber compound in Supercast RX, with its rubber matrix maintaining the physical integrity of the waterstop strip through dry phases, recovers more reliably from drying and re-swells consistently when the pool is refilled. For a commercial pool with frequent emptying and refilling cycles over a 30 to 50 year service life, Supercast RX is the more reliable specification than Supercast SW for the construction joint waterstop.