Procedure for Weathering Course in RCC Roof

A weathering course is a protective layer applied on RCC roofs to prevent water seepage, thermal stresses, and enhance the durability of the structure. It is particularly important in areas with high rainfall and temperature variations.

1. Purpose of Weathering Course

• Prevent water leakage into the roof slab.
• Protect the RCC slab from thermal expansion and contraction.
• Improve insulation against heat.
• Increase the lifespan of the roof.

2. Materials Required

1. Brick Jelly or Clay Brick Aggregate:
   • Crushed brick aggregates (sizes 20–40 mm).
   • Lightweight and thermally resistant.
2. Lime Mortar:
   • Mixture of slaked lime and fine sand (ratio: 1:2 or 1:3).
   • Acts as a binding material and insulator.
3. Waterproofing Compound (optional):
   • Additives to enhance water resistance.
4. Tiles or Finishing Layer:
   • Terracotta tiles, weatherproof clay tiles, or ceramic tiles.
5. Bitumen or Waterproof Membrane (optional):
   • For extra waterproofing in severe conditions.

3. Procedure for Laying Weathering Course

Step 1: Surface Preparation

1. Clean the RCC Slab:
   • Remove dust, loose particles, oil, or grease from the roof slab.
   • Wash the surface with water.
2. Repair Damages:
   • Fill cracks or holes in the RCC slab using a cementitious repair mortar.
3. Provide Slope:
   • Ensure the roof slab has a minimum slope of 1:100 to facilitate drainage.
   • Apply a screed layer if needed to achieve the slope.

1. Mix Lime Mortar:
   • Prepare a lime mortar with lime and sand in a ratio of 1:3.
   • Add a small quantity of water to achieve a workable consistency.
2. Spread Brick Jelly:
   • Spread brick aggregates or brick jelly evenly over the roof slab.
   • Compact the layer using wooden rammers.
3. Embed in Lime Mortar:
   • Pour the lime mortar onto the brick jelly layer.
   • Fill all voids between aggregates by tamping the mixture.
4. Level and Compact:
   • Level the surface and compact it well using a wooden float.

Step 2: Laying the Brick Jelly Layer

Step 3: Curing

1. Water Curing:
   • Start curing the weathering course after 24 hours.
   • Keep the surface moist by sprinkling water for at least 7–14 days.

Step 4: Finishing

1. Optional Waterproofing Layer:
   • Apply a bitumen coating or waterproofing membrane for additional protection.
2. Lay Tiles:
   • Place weatherproof tiles or terracotta tiles on the compacted layer.
   • Fix tiles with a cement mortar (1:3) for stability.
   • Fill joints with waterproof grout.
3. Final Slope Check:
   • Ensure the tile layer also maintains the drainage slope towards rainwater outlets.

4. Design Considerations

1. Thickness:
   • Brick jelly layer: 75–100 mm.
   • Tile or finishing layer: 20–30 mm.
2. Slope:
   • Provide a slope of 1:100 or 1:50 towards the water drainage points.
3. Drainage Points:
   • Ensure rainwater pipes are positioned at the lowest points on the roof.

5. Maintenance Tips

1. Regular Cleaning:
   • Keep the roof free from debris and stagnant water.
2. Inspect for Cracks:
   • Repair cracks or damage in the weathering course promptly.
3. Recoat Waterproofing:
   • Reapply waterproof coatings every 5–7 years for added durability.

6. Advantages of Weathering Course

• Provides thermal insulation to reduce heat ingress.
• Prevents structural deterioration caused by water seepage.
• Reduces roof maintenance costs.

7. Standards and Codes

• IS 456:2000 – General RCC design guidelines.
• NBC (National Building Code of India) – Roofing and drainage specifications.

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