A matrix of wood or iron is covered with successive layers of papers, pasted together so as to form pasteboard.
When mixed the concrete is carried at once to the position required, and if the matrix is quick-setting Portland cement this operation must not be delayed.
If the matrix, however, is originally crystalline it does not seem probable that perlitic structure can develop in it.
Above the diagram are given the names of the different classes of cast iron to which different stages in the change from graphite to cementite correspond, and above these the names of kinds of steel or cast iron to which at the corresponding stages the constitution of the matrix corresponds, while below the diagram are given the properties of the cast iron as a whole corresponding to these stages, and still lower the purposes for which these stages fit the cast iron, first because of its strength and shock-resisting power, and second because of its hardness.
Whatever matrix is used, it is almost invariably "diluted" with sand, the grains of which become coated with the finer particles of the matrix.