Phin says it is easy to find a recipe for a fireproof cement, but it is very difficult to find a cement that will stand a red heat. It is well to bear in mind the fact that no cement containing organic matter (such as glue, flour, oil, etc.) can maintain any adhesive power at a red heat, since all such substances are decomposed at that temperature. Cements containing oil, etc, may do to fill cracks, but not to hold two surfaces together. No cement can be depended upon for this purpose to any great extent. For some purposes, the Glass cements Nos. 1 and 2 answer very well. (1) Often a lute is required to join the covers to crucibles, or for similar purposes, so as to keep them air-tight when hot. A very valuable composition of the kind is made of glass of borax (fused borax), brickdust and clay, finely powdered together and mixed with a little water when used. No very great nicety is required in the proportions, but about 1/10 of borax is quite sufficient to bring the earths to that state of semi-vitrification which is desired.
Litharge may be used instead of the borax, but the latter is by far the better, as it promotes that thin spreading fusion which is most efficient. (2) A cement which is said to be useful for stopping cracks in iron vessels which are intended to be strongly heated, is made of 6 parts of clay, 1 of iron filings, and linseed oil enough for mixture. The oil will, of course, be speedily destroyed, but will leave enough carbonaceous residue to unite the remainder into a firm mass. Phin would prefer, however, to depend on the Iron cement Nos. 2, 3, and 4. (3) The following cement is said to be very hard, and to present complete resistance alike to a red heat and boiling water: - To 4 or 5 parts of clay, thoroughly dried and pulverized, add 2 of fine iron filings free from oxide, 1 of peroxide of manganese, 1/2 of common salt, and 1/2 of borax; mingle thoroughly; render as fine as possible; then reduce to a thick paste with the necessary quantity of water, mixing well. It must be used immediately. After application it should be exposed to warmth, gradually increasing almost to a white heat. (4) A fireproof cement is being introduced made from a material found in the Eifel Mountains. It is alleged by eminent professional men to be the only material known to science which possesses besides its plastic qualities the virtue of being fireproof.
Moistened with water, this cement forms an elastic mass, which can be exposed when dry to great heat without shrinking or showing any cracks. Such a cement should be peculiarly adapted for repairing defective fireplaces, cracks in retorts, etc, as mortar for fireproof buildings, and for the interior plastering of furnaces. The mode of its preparation is as follows: the cement is to be well mixed in a dry state, a small quantity of water is added and mixed well together. As a mortar it can be used in the ordinary way. In lining furnaces, however, care must be taken to press the cement well into the walls, so as to leave a smooth, even surface, as when dried by the air the cement easily crumbles and will not harden till ignited. Moreover it must not be treated roughly until it has been well burnt. Cracks in furnaces, retorts, etc, should be well cleansed and scraped, and if possible roughed before applying the cement. The parts to be mended should be damped beforehand. " An analysis by Dr. Bischof, of Wiesbaden, gives the following results: The cement is a pale grey, gritty substance, consisting of a good deal of fine dust, with angular and round particles of quartz. When mixed with water it is very sticky, compact, and easily moulded.
In 100 parts of the material dried at 248° F. (120° C.) there were:
Silica, chemically combined
Silica, mechanically mixed
Loss of heat....
As will be seen, the quantity of fusible matter, such as iron, etc, is very small indeed, if any. Under the fire treatment the cement showed the following results: After being heated to silver smelting heat, or about 1832° F. (1000° C), the cement turned to a grey colour, speckled with a few black spots, the fracture being earthy and porous. - (Scient. Amer)
(5) 20 ports fine river sand, 2 litharge, 1 quicklime, sufficient linseed oil to form a thin paste. Acquires a stony hardness. (6) 2 parts good clay, 8 sharp washed sand, 1 horse-dung; mixed thoroughly, and tempered like mortar. (7) Linseed or almond meal, mixed to a paste with milk, lime-water, or starch-paste; resists a temperature of 500° F. (260° C). (8) Clay is puddled with water, and to it is added the greatest possible quantity of sand, which has been passed through a hair sieve; the whole is worked up in the hands, and applied in coats more or less thick on vessels needing protection from the direct action of the fire. (9) 1 part of sifted manganese peroxide, 1 pulverized zinc white, sufficient commercial soluble glass to form a thin paste. To be used immediately. Becomes very hard, and presents a complete resistance to red heat and boiling water. (10) As a coating for glass vessels, to protect them from injury during exposure to fire, pipe-clay and horse-dung are made into a paste with water.
This composition is applied by spreading it on paper; it is used by pipe-makers, and will stand the extreme heat of their furnaces for 24 hours without damage. (11) Shredded tow, or plumbago, is substituted for the horse-dung.