Loam is a molding sand containing about 50 per cent sand grains and 50 per cent clay.
Loam molding was much used in the past for making large bronze castings and is still practiced in some shops, particularly in making huge manganese- bronze propellers.
In this method a substrate is made of bricks, wood and other material to the approximate contour of the casting. A very viscous slurry of water, clay and sand is daubed over the framework and worked to proper shape with sweeps. The mold is dried by forced hot air or torches.
No pattern is required, as sheet-steel sweeps are so shaped that they generate proper casting contour as the sweep arm is moved back and forth over a fixed spindle.
Such sweeps are used occasionally in making molds for large rolling-mill rolls where ordinary molding sand is used instead of a slurry.
The chief advantages of this process are savings in pattern cost and storage; pattern storage alone is an important and expensive item in most foundries.
Loam molding is slow and laborious, and special molders are required; all work must be done by hand as the process is very much an art.