When I run my finger across the mortar joints in a wall in a recently completed project a lot of sand falls to the ground. Does this mean the mortar is oversanded?
The mortar may or may not be oversanded. The sandy joints are more likely caused by cleaning the wall with a concentrated acid solution without first saturating the wall with water. The sandy surface results when cement paste brought to the surface during tooling is removed by the acid. This condition is commonly called acid burn. Along with a sandy surface, the mortar is darkened by a reaction between the acid and iron compounds found in most portland cement. Acid burn can be more than an aesthetic problem. Not soaking walls with water before cleaning them with concentrated acid solutions can introduce large quantities of chloride ions into the mortar. High concentrations of chloride ions accelerate the corrosion of embedded steel. I recommend having an analysis performed to determine both the mortar composition and if chlorides are present. If high chloride contents are found, perform more tests to find how deep the chloride has penetrated. If, at the depth of the embedded steel, the concentrations of chloride are greater than 0.2% by weight of the cement, corrosion may occur in the future.