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Seeing the various additives used for special application mortars over the past 1900 years, makes me appreciate the modern era's ability to synthesize.
Table 8: The effect of natural organic additives on lime-based mortars (4; 9; 5; 35)
Type of additive Natural compound
Increasing strength - Sugar, molasses, fats, fruit juices, rye dough, rice starch, gluten,
curdled milk, egg white, vegetable gums, casein, cheese, blood