Mass water-repellent: how it works, dosage and price

Mass water-repellent is a liquid admixture added to the concrete or mortar batch that cuts capillary water absorption by 70 to 90 % while preserving mechanical strength. The practical answers: it is dosed at 1 to 2 litres per m³ of concrete (0.5 to 1 % of cement weight), costs about 80-150 DH per litre as an admixture — and it never replaces a membrane under water pressure. Framing note: DAM sells neither admixtures nor waterproofed cement; this guide gives the benchmarks.

Two complementary mechanisms

Mass water-repellent acts on hardened concrete along two paths. The capillary one: silicate-based compounds react with the lime released by cement hydration to form insoluble gels that plug the capillaries — water loses its path upward. The hydrophobic one: tensioactive molecules (fatty acids, stearates, resins) coat the pore walls and repel water by surface tension — it beads on contact. The result: concrete becomes nearly impermeable to liquid water yet stays permeable to vapour — it keeps breathing and drying.

Dosage and use

• 1 to 2 litres per m³ of concrete or mortar, or 0.5 to 1 % of cement weight — follow the product data sheet.
• Add at batching, into the mixing water — never on the surface after the fact.
• Effectiveness depends on the mix: cement dosage ≥ 350 kg/m³, W/C ≤ 0.5, careful compaction — the admixture refines a well-designed concrete; it does not rescue a poor one.
• Mixing homogeneity is crucial: unevenly dispersed repellent leaves untreated zones.

Site admixture or factory-waterproofed cement?

The logic is simple: for a basement slab or tanking render, the admixture in standard cement does the job; for a heavily stressed structure, factory waterproofing secures homogeneity.

The limits you must know

Mass water-repellent treats capillarity: ground moisture, damp walls, facade absorption. It does not treat active cracks (water goes through the crack, repellent or not), poorly treated construction joints, or water under pressure — full pools, ponding roof terraces and tank rafts call for waterproofing systems installed per the rules. Selling mass water-repellent as membrane-in-a-bottle is the most commonly disproved promise on site; do not make it.

Our trade: standard CPJ 45 and CPJ 55 that carry your structures — delivered to Dakhla sites. For admixtures and systems, rely on the specialised manufacturers' data sheets.