Rubber felt, felt-paper, or Clark's patent felt, is used for a variety of purposes, such as covering damp walls, protecting silk and other wares from dampness during water-transit, covering telegraph-wire, roofing, etc. Although rubber is now entirely used, guttapercha, alone, or mixed with resins and other matters, has been employed. A pair of ordinary mixing-rolls, running at equal speeds, receive over each a cotton fleece, which is delivered from the carding-machines stationed on opposite sides, so that the 2 fleeces enter together between the rolls, and passing down through an opening in the floor, are led away, or rolled up. A soft dough is carefully laid between the rolls, and as the fleeces pass through, the rubber is squeezed into them. The fabric is vulcanised by incorporating sulphur with the rubber mixtures, and curing in the same way as ordinary spread fabrics. If made with good rubber and naphtha, it should not feel clammy nor soft, but should be dry and tough. Paper can be similarly treated; and, for damp walls, etc, would in many cases be as useful as cotton, while much cheaper. A few years ago, coppered cloth made from this felt was recommended for roofing purposes; it was abandoned principally because the rubber decayed, thus leaving nothing to support the metal.
By vulcanising, the rubber could be preserved, but it is not certain that the sulphur, by acting on the copper, might not be a source of fresh trouble. Iodine or bromine incorporated with the rubber would not be liable to this action on the copper. It should form a very useful protection for iron plates on ships, and might be used for a variety of purposes, as it could be cemented on, and, if the cement contained sulphur, or other curative agent, it could be vulcanised by holding a heated body against it.
White provides rubber surfaced fabrics with a permanent brilliant colouring, and slowly cures the rubber or guttapercha, whereby the surface of the fabric remains soft, flexible, coherent, tenacious, and has a peculiar leathery feeling. A filling compound, consisting of a mixture of 20 per cent. sulphur, 50 per cent. zinc oxide, and 30 per cent. suitable colouring material is mixed with the dissolved rubber to cure it and give it body and colour; the surface of the fabrics is coated with this composition. It is essential in preparing this filling that the ingredients be thoroughly dried before mixing, and mixed dry.