Nerizumi

What nerizumi means

Nerizumi is masonry in which stones or concrete blocks are laid with mortar or concrete filling the joints and the backing behind them, so that the whole wall acts as a single mass. It is also called neri-ishizumi, mortared stone walling. The opposite method, in which stones are stabilised only by their fit and by a backing of rubble without any binding material, is Karazumi, dry walling.

Nerizumi is common in civil works that resist flowing water or earth pressure. Water cannot easily pass through the joints and individual stones cannot shift, which suits erosion-control dams, river revetments and tall retaining walls. Because the wall also keeps water from draining through, weep holes are usually built into the body of a dam or wall.

The difference between nerizumi and karazumi concerns how stones are joined, which is independent of the pattern in which they are laid. Tanizumi sets stones diagonally, and Nunozumi lays them in level courses; either pattern can be mortared or dry. A record describing a dam as a tanizumi gravity nerizumi dam can therefore be read in three parts: the stones form a diagonal pattern, they are bound with mortar, and the dam resists water by its own weight.

Reading the records and the structure

Records for erosion-control dams often include the word in the type. The stone dams on the Shohoji River in Tottori Prefecture, from the first Tanukisawa dam through the Minamisawa series, are all described as tanizumi gravity nerizumi dams, with notes on the different slopes of their upstream and downstream faces and the shape of their weep holes. Dam No. 13 on the Mannai River in Niigata is likewise recorded as a gravity nerizumi dam. Slopes given as two or three bu express the horizontal offset per unit of height and describe the cross-section of the dam.

On site, look at the joints. If they are filled with mortar and show as thin lines on the face, the wall is nerizumi. If the stones interlock directly with only small stones packed into the gaps, it is dry walling. Dry walls have sometimes been mortared in later repairs, or pointed only on the surface, so appearance alone cannot settle the original method.