The mortar used for this purpose consists of ground fireclay which is mixed to grout of a consistency to suit the ideas of the furnaceman or the boss bricklayer, and usually kept hot during the mixing and to a considerable extent even during laying, by a steam coil in the bottom of the clay box.

This grout or mortar is generally mixed quite thin, poured onto the brickwork with a large dipper and flushed into the joints of the brickwork, both from below by sliding the brick being laid up against the one just laid, so as to fill the joint as nearly as possible with fireclay, and then from above by filling in the space and working the fireclay down between the two bricks with a trowel if any opening sufficient for that purpose exists, which in general it should not do.

Many of the difficulties with linings have been attributed by some furnacemen to bad bricklaying and particularly to wide joints. Some go so far as to insist that all unevenness must be removed from the bricks by chipping each individual brick where any appreciable amount of warpage exists, producing what is known as a case-knife job. This means that every joint shall be laid so close that it is impossible to get the point of a table knife into it.

Thick joints are undoubtedly very bad, but I have never seen any results produced by such extreme precautions which seem to me to justify the very greatly increased expense in laying the lining by this method. Careless work should on no account be tolerated, and if joints are found which are not thoroughly flushed the brickwork should be torn down and rebuilt properly. But as long as the firebricks themselves are made of clay suitably burnt, it has never been evident to me why the clay in the joints should not be burnt practically into the same structure as the brick itself, and in fact the brickwork which is torn out during the relining periods from the lower portion of the furnace where the heats have been high, comes out in blocks the line of whose breakage frequently pays little or no attention to the original joints in the brickwork, proving to my mind that when properly laid, the fireclay joint becomes, by the action of the furnace itself, almost as good as the brickwork.

This statement is, of course, predicated on the assumption that fireclay of the same quality as the brick will be used. If inferior clay be substituted it may act as flux for the brick themselves and absolutely destroy the lining.

The practice of making the fireclay thin may, in my judgment, easily be overdone, for the reason that if the clay is very thin, when the bricks are settled to place with a mallet, if there is the least particle of warpage, the brick gives enough to throw the thin clay out of the joint and when it springs back to shape again this joint is practically open. When the fireclay is made so thick, on the other hand, that it will just about pour from the dipper, it is too plastic to permit « this action and while the bricks may be driven up to a solid bearing with one another, the slight joint which remains after they are in contact is fairly filled with fireclay.