I recently had need to remove some Saltillo tile along the outside edge of a
concrete slab. The tile had been there for 15 years and had been mortared
in place with standard, grey thinset. Much - but not all - of the thinset
observed after popping the tiles was sugar white. The white areas were not
discernably different from the grey in hardness or adhesion.
Any idea why the mortar turned white?
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