Recommendations for cement mortar lining for cast iron mild steel and ductile-iron pipes and fittings for transportation of water
1986 Edition

Per the guidelines in Clause 7.1 and Table 2, the minimum cement mortar lining thicknesses are defined as follows: For cast or ductile iron pipes, diameters between 100 to 250 mm require a 3 mm average thickness with a minimum of 1.5 mm at any point; 300 to 900 mm need 5 mm average and 2.5 mm minimum; above 900 mm require 6 mm average and 3 mm minimum. For steel pipes, 100 to 300 mm diameter must have 5 mm average and 3 mm minimum; 350 to 900 mm need 8 mm average and 6 mm minimum; 1000 to 1500 mm require 10 mm average and 8 mm minimum; and over 1500 mm require 15 mm average and 12 mm minimum. The lining thickness at pipe ends may be reduced if the chamfer length is less than 50 mm. Mortar is typically mixed in a 1:2 cement to sand ratio by volume and must meet a compressive strength of at least 30 N/mm² after 28 days. Application is done by centrifugal casting to ensure uniform thickness and compaction, resulting in a durable and corrosion-resistant lining.

The standard mandates the use of well-graded sand ranging from fine to coarse, composed of inert granular particles that are hard, strong, durable, and free from coatings. This sand must be free from harmful organic impurities that could discolor or weaken the mortar. Grading tests are to be conducted following IS 460 (Part 1) -1985 standards and must conform to the limits specified in the standard's Table 1. Typically, sand passing various sieve sizes in specific percentages ensures proper grading. The mortar mix should maintain a cement to sand volume ratio of at least 1:2, and the resulting mortar must achieve a compressive strength of 30 N/mm² or greater after 28 days to guarantee a dense and resilient lining free from voids and segregation during application.

Before lining, the internal surfaces of pipes and fittings must be thoroughly cleaned to remove all dirt, oil, grease, and other contaminants. Any loose scale, rust, or metal projections exceeding the intended lining thickness must be eliminated to ensure proper adhesion. The surface should be sound, smooth, and free from defects such as inclusions, blisters, or voids that could compromise the quality of the mortar lining. This preparation ensures the mortar forms a dense, homogeneous, and defect-free lining that adheres properly, enhancing the durability and hydraulic efficiency of the pipe system.

The standard recommends moist curing methods to ensure proper hydration and strength development of the mortar lining. After the mortar has set, continuous wet curing should be maintained for a minimum of seven days by either sprinkling water over the lining (e.g., using a sprinkler hose at the pipe invert) or by covering the lining with moist sacking, canvas, or hessian kept constantly damp. For pipes exposed above ground, protection from direct sunlight using moist coverings is necessary to prevent thermal damage. Alternatively, membrane curing using approved compounds may be applied immediately after setting, subject to Engineer-in-Charge approval. Proper curing prevents shrinkage cracks, ensures a hard and durable lining, and achieves the required compressive strength of 30 N/mm² after 28 days.

Yes, the standard sets permissible limits for cracks and unbonded regions in the cement lining to maintain structural integrity. Unbonded areas are acceptable if their circumferential dimension does not exceed the nominal pipe diameter, and their longitudinal length is not greater than either the nominal diameter or 300 mm, whichever is larger. Longitudinal shrinkage cracks are allowed if their length is less than the greater of the nominal diameter or 225 mm. Circumferential cracks of any length and surface crazing are permitted. Any defects exceeding these limits must be repaired according to the specified repair procedures before the pipe is dispatched. Additionally, pipes should not be shipped until at least 21 days after lining to ensure proper curing.