Badly damaged sashes and handrails prove that the salt is the greatest cause of the rust of exposed iron. To combat this problem almost all such fittings were made of wood and aluminum was rarely used. Here only the effect of the salt on reinforced concrete structure will be discussed. Salt has damaged the concrete buildings in two principal ways. One is the use of sea sand as aggregate and sea water as concrete admixture. Though no record remains, the use of sea sand is the most probable explanation for the seashells visible in the reinforced concrete part of the oldest apartment building (No. 30, built in 1916). Although the record says that they used river sand for the other buildings and washed the iron bars with fresh water of distilled water which was precious to them, these iron bars must have been soaked with sea water while they were in the materials yard which was exposed to the wind from the sea. The process is as follows: salt laden air blown against the surface of an reinforced concrete structure penetrates into the gaps at junctions formed as a result of poor workmanship and into slight shrinkage cracks, so the reinforcing bars rust and expand, causing the cracks to enlarge and allowing the salt to penetrate further. “As sound concrete has a PH value of 12 to 13, a thin passive layer or protective crust is generally formed on the surface of the reinforcing bar and prevents the bar from rusting. But if the calcium hydroxide in the hardened cement comes into contact with the carbon dioxide in the air, the concrete becomes neutralised, the protective layer is not formed, and the reinforcing bars quickly rust. If concrete which has not been neutralised contains a lot of chloride, chlorine ions harm the protective layer and rusting of the bars occurs.” (“Nikkei Architecture” Feb 13. 1984)

In the early days, river sand was usually used as fine aggregate, but from the late Showa 30's, especially in Western Japan, the lack of river sand resulted in the use of sea sand. According to the report for the research committee into the problems caused by the use of sea sand (chairman: Koichi kisitani, Professor of the Univ. of Tokyo), in 1975, the percentage of use of sea sand is a little less than 30% on average over the whole of Japan, 81.1% in Chugoku District, 92.2% in Shikoku District, 74.5% in Kyushu district, and 86.6% in Okinawa district. The construction Ministry Regulations say that the ratio of salt contained in the aggregate should be less than 0.04%, but in practice this rule is not always observed and this has become a great problem in the architectural world. The kind of deterioration observable in an especially extreme form in building No. 30 is not simply a function of the aging of materials. The uniquely exposed conditions on this island accelerate the weathering process so that once cracks, caused by a variety of factors, appear, the reinforcing bars rust with great speed.