what is the paste used for bricks
Hydrated lime is not a necessary mortar ingredient. You can make mortar with just Portland cement, sand and water. The mortar that I used to permanently attach the brick and stone to my patios did not contain any hydrated lime. But adding hydrated lime to the mortar mix can be beneficial. The plasticity or workability of the mix will improve. When hydrated lime is added to the mix, the sand and the cement do not separate.