Overview
Sloped and industrial roofs present a different waterproofing challenge from flat terraces. GI sheet roofs expand and contract by several centimetres over a 30°C daily temperature swing — standard coatings crack and delaminate within one season because they cannot accommodate this movement. Asbestos cement (AC) sheet roofs deteriorate chemically with age, developing porosity and edge crumbling that no paint can seal permanently.
Prisci Constructions uses elastomeric polyurethane coatings, aluminium-faced bituminous coatings, and butyl rubber seam tapes specifically formulated for metal and AC sheet substrates. These systems elongate with the roof under thermal movement and seal lap joints and fastener holes without requiring sheet replacement — making them cost-effective for large industrial footprints.
We have waterproofed industrial roofs for HPCL, Air India maintenance hangars, and MES military structures — roofs that must remain operational and meet strict safety requirements throughout the treatment period.
Common Problems We Solve
- Dripping at lap joints and purlin connections in GI sheet roofs during monsoon — staining and rusting below
- Porous and crumbling AC sheet allowing rainfall to percolate through the sheet material itself
- Rust streaks and perforation at fastener holes in aged metal sheet roofing
- Ridge cap leakage — the longitudinal joint at the highest point collecting and channelling water inside
- Water entry at wall-to-roof junction (apron flashing failure) causing wall and column staining
- Seasonal leakage from skylight or translucent sheet panels installed without adequate lap sealing
Root Causes
- Thermal expansion stress at laps causing sealant to stretch and crack, creating open gaps during rain
- Fastener holes enlarging from vibration and repeated thermal cycling, losing their waterproof neoprene washers
- Galvanic corrosion where dissimilar metals contact (steel purlins + GI sheets) accelerating sheet perforation
- AC sheet carbonation and chemical breakdown in Hyderabad's alkaline rainwater creating micro-porosity
- Inadequate lap dimension or improperly bedded laps at original installation not sealed with mastic
- UV degradation of original bituminous or silicone sealants at joints over 8–10 years of exposure
Our Approach
A roof walk-over is conducted with a checklist for every lap, ridge, fastener point, flashing, and penetration. Leak locations from inside the building are correlated with roof features above. Areas of corrosion, perforation, and seal failure are photographed and measured.
We specify whether the roof requires targeted seam-and-fastener treatment or a full-coverage elastomeric coating. Corroded sheets requiring replacement are identified separately. Material quantities, access scaffolding requirements, and work sequences for occupied facilities are planned.
Seams are cleaned, primed, and sealed with self-adhesive butyl tape before the liquid coating is applied. Airless spray or roller application proceeds systematically from ridge to eave. Post-application hose test is conducted at all previously identified leak points to confirm seal.
Materials Used
Metal and AC sheet roofs require materials with high elasticity (>200% elongation) and excellent adhesion to non-porous substrates — standard cementitious products are unsuitable; we specify only elastomeric polymer systems tested for cyclic thermal movement.
Our Process
Roof Condition Survey
All roof surfaces, laps, fasteners, ridges, and flashings are inspected and mapped. Interior leak stain locations from inside the building are noted and GPS-correlated with roof features to prioritise sealing sequence.
Loose Fastener & Perforated Sheet Replacement
Failed or missing fasteners are replaced with new neoprene-washered self-drilling screws. Sheets with extensive corrosion perforation (beyond sealable area) are replaced before coating — applying coating over heavily corroded metal only postpones the problem.
Surface Cleaning & Rust Treatment
Roof surface is high-pressure washed to remove dirt, algae, and loose rust. Remaining rust is treated with a rust converter (phosphoric acid-based) and allowed to cure. AC sheet surfaces are cleaned and any friable areas consolidated with penetrating primer.
Seam Sealing with Butyl Tape
All longitudinal and transverse lap joints, ridge caps, and apron flashings are sealed with 75mm-wide self-adhesive butyl rubber tape pressed firmly into all gaps. This addresses the primary infiltration routes before the surface coating is applied.
Primer Application
Rust-inhibiting metal primer is applied across the entire roof surface. This improves elastomeric coating adhesion and provides additional corrosion protection for the metal substrate. Adequate drying time is observed before the next coat.
Elastomeric Coating Application
Two or three coats of elastomeric waterproofing coating (BASF MasterSeal 6100 or equivalent) are applied by airless spray or long-pile roller, achieving the specified DFT of 800–1200 microns. Reflective aluminium or white pigment provides UV protection and heat reduction.
Hose Test & Inspection
On completion, a hose test simulating rainfall is conducted at all previously identified leak points, lap joints, and ridge areas. Any re-emergence of leakage is immediately traced and remedied. A written sign-off report is issued before the project is closed.
Frequently Asked Questions
Related Projects
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