IS 2645 : 1975Integral Cement Waterproofing Compounds - Specification

IS 2645 specifies integral cement waterproofing compounds — admixtures added at the mixing stage to reduce concrete permeability. They come as powder or liquid and act by either pore-blocking (hydrophilic crystalline) or pore-lining (hydrophobic stearate/silicate).

Use IS 2645-compliant compounds when: - Water-retaining structures (tanks, sumps, swimming pools) — supplements IS 3370 Part 2 - Basement rafts, retaining walls below water table - Roof slabs (waterproofing concrete in addition to membrane systems) - Mass concrete pours where bleed-channel reduction is desired - Marine and coastal exposure (IS 456 Clause 8.2 Severe and above)

IS 2645 is one tool, not a complete waterproofing strategy. Even with a compliant integral compound, you still need: proper cover (IS 456 Clause 26.4.1), low w/c (≤ 0.50 for water-retaining), construction-joint detailing (waterstops), and often a surface-applied membrane on the wet face.

IS 2645 acceptance is by comparison with a control mix (same cement, aggregate, w/c) — admixed concrete must outperform the control on permeability while not degrading strength.

Permeability (key test): - Test method: water impermeability per IS 3085 (depth of water penetration under sustained pressure) - Acceptance: ≤ 25 mm penetration depth at 7 days for treated; treated must show < 50 % of the control's penetration depth at 28 days

Compressive strength of treated concrete vs control: - 7-day: ≥ control − 5 % - 28-day: ≥ control (no strength penalty) - 90-day: ≥ control + 5 % (most pore-blocking compounds gain over time)

Setting time deviation (Vicat): - Initial: −90 to +120 minutes vs control - Final: similar window

Workability impact: - Slump deviation vs control at same w/c: ±10 %

Chemical limits: - Chloride content: ≤ 0.2 % (so total Cl⁻ in concrete stays below IS 456 Clause 8.2.5.2 caps) - pH: 9-12 typically (verify supplier datasheet) - Free alkalinity: declared on datasheet

Dosage range: typically 0.5-2 % by mass of cement; supplier-specific. The dosage that meets the permeability target is established by trial mix, not assumed.

• IS 456:2000 — RCC design, durability provisions in Clause 8.
• IS 3370 Parts 1-4 — water-retaining structures (the core design code that drives integral waterproofing).
• IS 9103:1999 — admixtures specification (IS 2645 sits alongside this for compatibility).
• IS 3085:1965 — water permeability test method (referenced by IS 2645 acceptance).
• IS 10262:2019 — mix design (IS 2645 compounds enter as a Type II admixture in trial mix).
• IS 13530 — quality of water for water-retaining concrete.
• IS 4990 — plywood for shuttering of water-retaining structures (smooth finish reduces capillary entry points).
• IS 2645:2003 — the 2003 revision is the current authority for new contracts (the 1975 version is largely retained but tighter dosage and chloride limits).

1. Treating integral waterproofing as a substitute for membrane. It isn't. Below the water table, in roof slabs, and on tank wet faces, you still need a surface membrane (bituminous, EPDM, polyurea) for a defence-in-depth strategy. IS 2645 reduces capillary water transport in the *body* of the concrete; cracks bypass it entirely. 2. Ignoring crack control. A waterproofed concrete with shrinkage cracks leaks just like ordinary concrete. The first defence is mix design (low w/c, low cement content, fly-ash blend), then IS 456 Clause 35.3.2 crack-width limits, *then* IS 2645. 3. Site-overdosing 'for safety'. Above the manufacturer's range, integral waterproofing compounds delay setting, reduce strength, and can cause efflorescence. Stick to trial-mix dose. 4. Field mixing of solid powder integral compound at the mixer. Uneven distribution. Premix with cement at the batch silo or use the liquid form metered through the admixture system. 5. Using IS 2645 compound and a shrinkage-reducing admixture without compatibility test. Some chemistries clash and produce gross workability anomalies. Always trial-mix before site supply. 6. Specifying 'IS 2645 waterproofing' without the dose-and-target permeability. The contract should read e.g., `Integral cement waterproofing compound conforming to IS 2645:2003, dosed per supplier recommendation but not less than 1 % by mass of cement, achieving ≤ 20 mm water penetration depth at 28 days per IS 3085.` That ties the supplier and the contractor to a measurable outcome. 7. Forgetting the construction joints. Integral waterproofing does nothing for cold joints. Pair with PVC waterstops at every horizontal and vertical joint in water-retaining structures.

Layered defence for a typical underground RCC tank:

1. Mix design — w/c ≤ 0.45, OPC + 25-30 % fly ash (or PPC), cement content 350-380 kg/m³, IS 456 Severe / Very Severe exposure compliance. 2. Integral waterproofing — IS 2645 compound at 1-1.5 % cement mass; adds the body-permeability barrier. 3. Crack control — distributed steel per IS 456 Clause 26.5 and IS 3370 Part 2; crack-width limit 0.2 mm (severe exposure), 0.1 mm (very severe / liquid-retaining). 4. Construction joint detailing — PVC waterstops in horizontal and vertical joints, surface preparation (laitance removal, joint roughening) before subsequent pour. 5. Surface membrane — bituminous primer + 2 coats SBS-modified bitumen membrane on the wet face (water side); polyurethane on the dry face for protection during backfill. 6. Curing — 28-day water curing of the concrete itself (the most under-done step that eliminates the value of all the upstream investments).

IS 2645 is a piece of the puzzle. Audit the full strategy, not just the admixture spec.