The Cement Problem

From John Messina's book about Alamos architecture, which I highly recommend:

"In recent times, Portland cement has been added to the plaster mix in order to make it harder and less likely to wear away. This combination, however, produces a hard and impervious coating that prevents any of the inevitable moisture that has entered the wall from escaping. Water will thus be retained, and the wall will gradually erode from the inside. Unfortunately, many contemporary masons and plasterers working in Alamos have resorted to cement plasters. Thos entities and authorities charges with preservation oversight urgently need to educate the local trades and owners regarding this problem."