Interesting! That brings me back to my lime wash questions. Weak acids (vinegar) are used to isolate casein from milk. The resulting casein is added to lime wash (water saturated with calcium hydroxide) becaues it forms calcium caseinate, which binds much better than calcium carbonate (lime + CO2).
So here's the recipe for "Elmer's" Glue. What ingredient do you think is doing the binding?
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1 quart skim milk
3/4 tablespoon baking soda
1 tablespoon white vinegar
10 ounces water
Place milk and vinegar in a double boiler. Cook on low heat and stir as curds form. Drain off liquid. Wash remaining mass with water until the vinegar smell is gone. Put into a clean bowl. Dissolve baking soda in water. Pour over curds and stir until a white paste forms. Seal in suitable containers.
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This tells me that you probably don't want too much glue in the mix or it will weaken it in the long run??? I can't imagine calcium caseinate being better than calcium carbonate for long-term stability. My guess is that's why it's mostly used for adding new concrete to old concrete, rather than as a fortifier. It sounds like the purpose is strictly to get the two to initially stick together, allowing other reactions to stabilize the bond.
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