IS 2115:1980 is the Indian Standard (BIS) for flat-roof finish: mud phuska. This code specifies the standard practices for laying mud phuska flat-roof finishes, a traditional and cost-effective technique used primarily in hot-arid regions of India for thermal insulation and waterproofing. It details the required soil properties, surface preparation including bitumen application, preparation of the soil-straw mix, laying procedures, and final paving with burnt clay brick tiles.
Code of practice for flat-roof finish: mud phuska
| Parameter | IS Value | International | Source |
|---|---|---|---|
| Roof Slope / Gradient for Drainage | 1 in 40 to 1 in 60 | Designed fall of 1:40 to achieve a finished fall of 1:80 | BS 6229:2018 |
| Insulation Material | Puddled clay mixed with wheat straw (bhusa) | Soil-aggregate mixtures with defined clay/silt/sand ratios, potentially with straw fibre. | HB 195-2002 |
| Average Insulation Thickness | 10 cm (compacted) | Varies by climate and required U-value; typically 120mm - 200mm for PIR/EPS foam. | BS 6229:2018 |
| Compaction Method | Manual ramming with wooden 'thapies' | Pneumatic or manual rammers used to compact material in controlled layers (lifts) of 100-150mm. | HB 195-2002 (for rammed earth) |
| Drying/Curing Time | Allowed to dry for 2 to 3 days before applying top finish. | Drying is critical and can take weeks to months depending on thickness and weather, monitored by moisture content. | HB 195-2002 |
| Protective Top Finish | Brick tiles laid over 12mm mortar, over a slurry of cement/cow dung (gobri). | Ballast, paving slabs, green roof media, or an exposed traffic-resistant membrane surface. | BS 6229:2018 |
| Dry Bulk Density | Approx. 1600-1800 kg/m³ | Approx. 1700-2200 kg/m³ (for structural rammed earth) | HB 195-2002 |