Frequently Asked Questions

What is the correct step-by-step application procedure for using MC-Stop to plug an active water leak gushing through a crack in a basement wall, and what should be done after the leak is stopped to achieve a permanent waterproofing repair?

Plugging an active water leak through a crack in a basement wall with MC-Stop involves a sequence of preparation, leak plugging, and then a comprehensive waterproofing system application to achieve a permanent repair. Many contractors make the mistake of treating the MC-Stop plug as the permanent repair solution — it is not. MC-Stop stops the active water flow (emergency intervention), but the permanent barrier against future water ingress through the basement wall must be provided by a compatible waterproofing system applied after the plug has hardened. The complete procedure is as follows. Preparation of the leak point. Identify the precise location of the water ingress point — this is usually not just a hairline crack but a crack with separation, a cold construction joint (the joint between separately poured concrete sections), a pipe penetration, or a tie-rod hole. Chase the concrete at the leak point using a 20 mm wide cutting disc or chisel to form a V-shaped or undercut groove approximately 20 mm wide and 20 mm deep (the undercut or V-shape is critical as it allows the MC-Stop plug to lock mechanically into the groove even against water pressure — a straight groove will be pushed out by the water pressure before the cement sets). Chisel back the full length of the crack or the full perimeter of the joint. Remove all loose concrete and dust from the groove with a stiff brush and compressed air or water. Do not try to dry the substrate — MC-Stop works in the presence of running water. Mix MC-Stop. Mix the required quantity of MC-Stop powder in a dry container — never mix on a wet surface or in a damp container. Add water sparingly (approximately 3 to 4 parts powder to 1 part water by volume, or refer to the current TDS) and work quickly with a gloved hand or trowel to form a stiff, non-sticky putty-like ball in 15 to 20 seconds. Do not use a mechanical mixer — the heat generated by hand mixing accelerates setting and the stiffness of the mix can be felt and controlled. Mix only a quantity that can be used in one application — do not mix large batches as the material will set in the mixing container. Apply the MC-Stop plug. Shape the mixed putty into a cone or cylinder slightly larger than the groove cross-section. Press the putty firmly into the groove at the point of maximum water flow, holding it in position with sustained firm hand pressure. Hold the plug in place for 30 to 90 seconds without releasing pressure. As the material heats up and stiffens (the rapid exothermic set is clearly felt through the glove), the water flow will slow and stop. Do not release hand pressure until the material has hardened and the water flow has completely stopped. If the water pressure is very high or the flow is too rapid to allow plugging by hand, drill a 12 to 20 mm hole at the base of the crack (the lowest point of water ingress) and insert a plastic tube to direct the water away from the repair area (a drain tube approach), allowing the remaining crack area to be plugged with MC-Stop without fighting the full water head pressure. After the full crack is plugged, the drain tube is removed and the hole is plugged last. After leak plugging — permanent waterproofing. Allow the MC-Stop plugs to harden for a minimum of 30 to 60 minutes. Apply a scratch coat of MC-Bauchemie Nafucryl crystalline waterproofing slurry (two coats, 1.5 kg per square metre per coat) over the full wall and floor surface of the basement, including over the MC-Stop plugs and the surrounding concrete surface. Nafucryl contains cristallinite (proprietary crystalline agents) that react with cement and water to form insoluble crystals that permanently block all capillary pores and microcracks in the concrete, providing a barrier against hydrostatic water pressure. Allow Nafucryl to cure for 7 days under damp curing. For below-ground structures under continuous hydrostatic pressure, a two-coat Nafucryl system applied to the negative (water) face is the preferred permanent waterproofing strategy, providing a breathable, flexible, self-healing crystalline barrier that can re-seal new microcracks over time without maintenance. Consult Space Arc Engineering for system design and application guidance for specific basement waterproofing projects.