Method of field testing of building lime
1986 Edition

The hydrochloric acid test, as per IS 1624 Clause 4.1, involves placing powdered lime into a 50 ml graduated cylinder and gently tapping until it settles to approximately 5 ml with a smooth surface. Then, dilute hydrochloric acid (1:1) is carefully added up to the 25 ml mark along a glass rod to avoid wall smearing. The mixture is stirred thoroughly with a glass rod, ensuring minimal inert residue remains. Additional acid is added dropwise while stirring until no bubbling (effervescence) is observed, signifying complete reaction. The sample is left undisturbed for 24 hours to check for gel formation, which indicates lime quality. This method helps in assessing impurities and the reactivity of the lime.

Field detection of impurities in lime, guided by IS 1624, begins with a visual check for color uniformity and lumpiness; pure building lime should be white without coarse lumps. Lumpy lime may suggest the presence of quicklime or unburnt limestone; quicklime is porous whereas unburnt limestone is dense. The hydrochloric acid test reveals impurities by observing the intensity of effervescence—excessive bubbling indicates a high presence of calcium carbonate impurities. Additionally, immersing lime balls in water helps classify quality based on disintegration: rapid disintegration points to lower classes (C or D), minor expansion with surface cracks indicates intermediate classes (B or E), and no disintegration signifies high-quality lime (Class A). These simple tests provide quick impurity insights prior to detailed laboratory analysis.

The plasticity test on blotting paper, described in IS 1624 Clause 7.2, offers a quick qualitative measure of lime's workability and fineness. Lime exhibiting good plasticity will spread smoothly over blotting paper without gritty particles, indicating it is well-hydrated, finely ground, and reactive—qualities desirable for masonry and plastering applications. Conversely, poor plasticity, characterized by a gritty or uneven spread, suggests the presence of unreacted quicklime, coarse particles, or impurities, which can adversely affect workability and bonding. Although this test is less precise than laboratory analyses, it serves as an effective field check to ensure the lime's suitability.

IS 1624 recommends assessing lime mortar workability on-site primarily through the mason's practical judgment. The mason throws a handful of freshly mixed mortar onto the intended working surface with the same force used for rough-casting. The evaluation focuses on the extent of the area covered by the mortar and the amount adhering to the surface; good workability is indicated if the spread area is at least twice the size of the handful and most of the mortar sticks to the substrate. Additionally, comparing the mortar's plasticity against a known standard by checking for smoothness and absence of grit helps confirm quality. This method is fast, based on tactile and visual feedback, and suitable for field conditions.

Poor-quality lime can be detected visually by several signs as per IS 1624. The color should ideally be white for Class C and D limes used in whitewashing; any yellowish or grey shades may indicate contamination or substandard quality. The presence of lumps suggests either quicklime or unburnt limestone; quicklime is porous whereas unburnt limestone is dense. The hydrated lime should be free from coarse, gritty particles exceeding 2.5 mm in size. In the hydrochloric acid test, rapid disintegration or formation of cracks and expansion points to lower-grade lime (Classes C or D), while excessive effervescence during acid application indicates unburnt or improperly processed lime. Recognizing these characteristics helps prevent use of unsuitable lime prior to comprehensive laboratory testing.