IS 11433 (Part 1) : 2000Specification for one part gun-grade polysulphide-based joints sealants, Part 1: General requirements

IS 11433 Part 1:2000 is the specification for one-part, gun-grade polysulphide-based joint sealants — the elastomeric sealant used in expansion joints, control joints and movement joints in buildings, runways, water-retaining structures and bridge decks. "One-part" means factory-mixed, cures by moisture from the air; "gun-grade" means a non-sag paste applied with a sealant gun (as opposed to pourable Part 2 grade).

It sits inside the joint-sealing stack alongside the substrate codes:

• IS 11433 Part 2 — *pourable-grade* (two-part) polysulphide for horizontal joints (floors, decks, water tanks)
• IS 12118 (Parts 1 & 2) — two-part polysulphide sealants (gun-grade and pourable)
• IS 456 — RCC, including expansion-joint requirements
• IS 3414 — design and installation of joints in buildings
• IS 1834 — hot-applied bitumen joint sealing (the older, lower-spec alternative)

Composition. A one-part polysulphide elastomer in a 'gun-grade' (paste) consistency — extruded from a cartridge, cures on exposure to atmospheric moisture. Typical hardness Shore A 25-40 after cure.

Movement accommodation. The sealant must accommodate ±25% movement of the original joint width without cohesive or adhesive failure. This is the headline performance number — it tells the designer the joint width required for the calculated expansion-contraction range.

Joint geometry rule. For movement-accommodating sealants, the joint depth-to-width ratio must be controlled — typically depth = width / 2 (or 6 mm minimum, whichever is greater). A bond-breaker tape or backer rod at the bottom of the joint prevents three-sided adhesion (which kills movement capacity).

Substrate adhesion. Tested on concrete, mortar, glass, anodised aluminium and natural stone — the sealant must bond after appropriate priming. Adhesion failure on damp concrete or oily formwork is the #1 site issue.

Recovery. After 24-hour compression at 60% then release, the sealant must recover to ≥ 80% of original dimensions. Loss of recovery = loss of movement capacity = leaking joint.

Service life. Type-tested for a minimum 5-7 year exterior service life in Indian climate (sustained UV + monsoon cycling).

Project: A reinforced-concrete roof slab, 25 m long, with one full-depth expansion joint at the mid-span. Sealing this joint above-deck against monsoon ingress.

Step 1 — calculate movement. Concrete thermal coefficient α ≈ 10 × 10⁻⁶ /°C. Roof temperature swing in central India ≈ 40 °C (peak summer day vs cold winter night for an exposed slab). Slab length tributary to the joint = 25 m → 12.5 m on each side from mid-joint. Free movement = 25 × 40 × 10⁻⁶ × 1000 = 10 mm range (each side contributes 5 mm).

Step 2 — pick the joint width. Sealant must accommodate ±25% of joint width. For a 10 mm movement range (±5 mm), minimum joint width = 5 / 0.25 = 20 mm. Use a 25 mm joint to give a comfortable margin against installation tolerance.

Step 3 — joint depth. Depth = width / 2 = ~12 mm (or set by backer rod). Insert a closed-cell polyethylene backer rod (slightly oversize so it grips the joint walls) at 12 mm below the slab top surface.

Step 4 — surface prep. Joint walls must be clean, sound, dry. Grind off laitance, blow out dust. Apply the manufacturer's specified primer (typically epoxy for concrete) — let it tack-dry per data sheet.

Step 5 — gun the sealant. Cut the cartridge nozzle to the joint width, gun in a continuous bead, tool the surface flush (concave, never proud). Allow the full skin-over time (~24-48 h in monsoon, 6-12 h in dry season) before exposure to water.

Step 6 — secondary protection. For a roof expansion joint, add a PVC or metal expansion-joint cover strip over the sealed joint to take pedestrian/maintenance traffic and to shield the sealant from direct UV. The sealant is the waterproof line; the cover strip is the wear line.

1. No backer rod. Without a backer rod, the sealant bonds to three faces (both walls + the slab below). Movement now tears the sealant instead of stretching it. Result: split joint by the second monsoon. Always use a bond-breaker.

2. Wrong joint width. A 10 mm joint with 12 mm calculated movement cannot work — period. The math comes first; the sealant doesn't fix an under-sized joint.

3. No primer on concrete. IS 11433 Part 1 names the substrate primers in the manufacturer's data sheet. Skipping primer on concrete halves adhesion. Detected only when the joint starts leaking 18 months later.

4. Applying in monsoon. One-part polysulphide cures via atmospheric moisture, but standing water in the joint or condensation during cure causes blistering and surface bubbling. Cover the joint until cure is complete.

5. Using bituminous filler in lieu of polysulphide. IS 1834 bitumen filler is cheaper but has zero movement-accommodation capacity. Specifying it in a heat-cycled exposed joint is design-grade negligence — switch to IS 11433.

6. No protection over the bead. A roof or footpath expansion joint without a metal/PVC cover strip wears the sealant out in 18-24 months under foot traffic and UV. Cover strip is mandatory in trafficked areas.

• IS 11433 Part 2 — pourable-grade (two-part) polysulphide for horizontal floor/deck joints
• IS 12118 Parts 1 & 2 — two-part polysulphide sealants (gun-grade and pourable — slightly different cure chemistry, longer pot life)
• IS 3414 — code of practice for design and installation of joints in buildings (the design parent)
• IS 456 — RCC code, including expansion-joint spacing rules
• IS 1834 — hot-applied bitumen joint sealing compounds (the older, non-movement-accommodating alternative)
• IS 9963 — joint sealing for concrete pavements
• IS 13384 — silicone sealants for building construction (alternative for high-UV applications)

Polysulphide sealants under IS 11433 are the workhorse joint sealant for Indian construction — buildings, swimming pools, water tanks, runway slabs, retaining-wall vertical joints. They tolerate the monsoon-to-summer climate cycle, bond well to primed concrete and metal, and accept the ±25% movement that most building joints actually see.

The field-failure pattern is consistent and instructive: 3 out of 4 failed polysulphide joints fail for the same reason — no backer rod, three-sided adhesion, sealant torn by the first temperature swing. Spec the backer rod, draw the backer rod on the detail, and check the backer rod on site. Costs Rs. 30 per meter; saves a re-doing the entire joint at handover.

For water-immersed joints (tanks, swimming pools, water-retaining structures), the manufacturer's data sheet matters more than the IS spec — confirm the specific product is certified for prolonged water immersion (some are skin-applied only). For high-UV exposure (south-facing parapets, runway joints in arid regions), consider silicone (IS 13384) instead — it weathers better than polysulphide.

The written BOQ line should always specify: "polysulphide sealant to IS 11433 Part 1, applied over closed-cell PE backer rod, on primed substrate, finished concave, with metal/PVC cover strip in trafficked locations." That one line catches all five common site mistakes.