The walls are first plastered with lime and hair mortar, having, for the best class of work, some cement added to improve it. After this has set, a second coat of mortar, mixed so as to be fat, is spread as evenly as possible over the last coat, and while this is quite soft the stones to be used are dashed forcibly against the work, to which they adhere. Care should be taken to see that the sand and stones or pebbles used are free from dirt, and if any clay is found mixed with the sand it will require washing. The stones should be screened so that they will be of about the same size. Sometimes a coat of lime-white and sometimes ochre is used for colouring the roughcast.