Tag: Lime Mortars

Tests for Strength of Lime Mortars

Tests for Strength of Lime Mortars

Two bricks are joined flat in a cross fashion one over the other with 12 mm mortar joint. Bricks are thoroughly soaked in water before joining and cured for 7 days after they are jointed. Load required to separate them at joint gives the adhesive strength of mortar which should not be less than 1.4 kg/sq. cm for I lime to 2 sand mortar. For testing tensile strength, briquettes are made (as for cement test), and cured for 24 days by immersion in water. A good hydraulic lime should have an ultimate tensile strength of at least 7 kg/sq. cm and a fat lime 2.8 kg/sq. cm, with 1 : 3 lime : sand mortar. The compressive strength should be 4 to 5 times its tensile strength. Mortar consisting of 1 part good quality kankar lime and 1 part sand should develop a compressive strength of over 50 kg/sq. cm after 3 months and twice that after two years. A pure surkhi mortar gives a breaking strength of about 5.6 to 6.3 kg/sq. cm if left in dry air, and 21 to 25 kg/sq. cm if left immersed under water.

Compressive strength of 1:4 cement-sand mortar after 3 months is over 210 kg/sq. cm. Simple method of testing the strength and suitability of a particular limestone or kankar is to burn the limestone, produce lime, mix it with the required proportion of sand and test the mortar as described above.

Lime Mortars

Lime Mortars

Lime mortars require grinding to slake the unslaked particles and to make an intimate mixture of the materials. Lime/surkhi mortars are ground in two operations, first only the lime and surkhi are ground together and then sand is added and again ground. For big jobs grinding is done in a bullock-driven mortar mill (or machine). In a mortar-mill the diameter of the track should not be less than 8 m. No piece larger than 6 mm should be introduced in a mortar mill. For small jobs grinding can be done by ponding the ingredients in a small pit and mixing. Small quantities of mortar can be mixed by repeatedly turning over the materials with a shovel, and afterwards with a trowel, so as to mix them very thoroughly.