In applying asbestos paste to a boiler shell, hot-water pipes, steam pipes, etc., first rub some of the paste on the surfaces with the hand or with a piece of cloth or canvas, leaving it quite rough so as to form a key for that which follows. The first coat is rubbed on to ensure the whole having actual contact and holding securely to the boiler. When the paste is dry, with a trowel apply the remainder in about 1/2-in. layers, leaving the surfaces rough (except the final one), and letting each coat dry before applying the next. The surfaces treated should be quite hot whilst the paste is being applied with the trowel; the heat slightly opens the pores in the metal, and this prevents cracking or shelling afterwards.