Waterstop-RX (also referred to as RX ) is a black coloured flexible strip designed to stop water leaking through concrete construction joints. A typical application would be to seal the centre of the edge of a poured floor where it meets the footings and base of a concrete or block wall. The RX is glued into place at least 80mm below top of the concrete pour and then the concrete is poured against it. Waterstop-RX is comprised of 75% Sodium Bentonite and 25% Butyl Rubber. On contact with water the Sodium Bentonite expands creating a pressure resistant seal. Waterstop-RX has been independently tested to withstand 60 metres of hydrostatic pressure.