places. The softening point oi this brick is 

 approximately 2,905° F. and its maximum 

 expansion is one-sixteenth inch per foot at a 

 temperature of approximately 2,200°. Con- 

 crete will seldom withstand a temperature in 

 excess of 1,000° F. and the normal temperature 

 in the average camp stove or fireplace ranges 

 from 800° to approximately 1,500°. The co- 

 efficient of expansion of fire-clay brick is about 

 one-third or one-fourth of the coefficient of 

 expansion of iron. In decimal figures, this co- 

 efficient is 0.000005 for each degree centi- 

 grade. 



Fire-clay brick is usually laid on its natural 

 bed, but sometimes it is laid on side. In laying 

 iire-clay brick in camp stoves and fireplaces 

 which are exposed to the weather, the fire-clay 

 mortar should be a mixture of fire clay with ap- 

 proximately 20 to 25 percent of portland cement 

 by bulk. This mortar is "buttered" lightly with a 

 trowel on the surfaces of the brick and should 

 make a joint approximately one-sixteenth inch 

 in thickness. If the ftre clay is spread too thick- 

 ly, it virill destroy the strength of the fire-clay 

 brick hning. This joint should be just as thin 

 as it is practicable to make it. 



The reason for keeping fire-clay mortar very 

 thin on the surface of the bricks is because the 

 lire clay used in the joint between the bricks is 

 not as resistant to heat as is the fire-clay brick 

 itself. The joint would, therefore, have a tend- 

 ency to shrink and cause damage if the joint 

 were even as thick as one-fourth of an inch. 

 This thin joint is sometimes procured by dipping 

 the fire-clay brick in hre clay of a rich, creamy 

 consistency and pushing the brick into place by 

 rubbing the top brick back and forth on the 

 lower brick. 



Many instances are observed in which ap- 

 parent defective construction has not produced 

 satisfactory results in the construction of the 

 fire-clay brick lining. 



For the best results, fire clay used to create 

 a bond between fire-clay brick should be sub- 

 jected to a temperature exceeding 1,600'^' to 

 1,800° F. in order to cause the chemical reac- 

 tion required to make the joint permanent. It 

 is doubtful if the heat produced through the 

 normal use of any firebox is sufficient to cause 

 the permanent chemical change necessary to 

 produce the desired result. 



The best results are procured in the construc- 



tion of fireboxes for outdoor camp stoves and 

 fireplaces when, to the fire clay, there is added 

 by volume approximately 20 to 25 percent of 

 Portland cement or similar cement. The addi- 

 tion of this cement produces a "cold set", 

 which the subsequent heat further fixes, with 

 the result that this fire clay and cement joint 

 creates a solid and permanent bond. 



It is desirable, in any event, whether or not 

 cement is added to the fire clay, to subject the 

 lining of the fireplace to an intense fire for at 

 least 4 or 5 hours. If fire clay is used without 

 the addition of cement, this fire should be suffi- 

 ciently intense and continued sufficiently long 

 so that the inside surface of the brick shows 

 evidences of starting to glow. Unless this pro- 

 cedure is adopted the joint will be damaged by 

 rain and by freezing. 



There are on the market air-setting, high- 

 temperature cements which vnll create an 

 excellent bond under a cold set. It is doubtful 

 if high-temperature cements will be as perma- 

 nent as the bond produced by a mixture of fire 

 clay and portland cement or its equivalent, as 

 above suggested. 



The average mortar will not usually with- 

 stand any considerable amount of heat because 

 of the content of lime which fluxes under heat 

 and because of the content of sand which does 

 not have refractory qualities to the extent re- 

 quired in these joints. 



In filling the space between the back of the 

 fire-clay brick lining and the face of the stone 

 masonry shell or covering, the fire clay, prop- 

 erly moistened, should be mixed with pulverized 

 calsined fire clay in the proportions of one part 

 fire clay to two or three parts of the calsined 

 fire clay. It is not recommended that this space 

 be filled with pure fire clay for the reason that 

 the natural fire clay will shrink to a consider- 

 able extent when subjected to intense heat. 

 The fire clay should be mixed as above indi- 

 cated with calsined clay because the calsined 

 clay has been subjected to a considerable heat 

 and will therefore not be subject to any con- 

 siderable amount of shrinking. 



The space between the fire-clay brick lining 

 and the stone masonry backing must be com- 

 pletely grouted and thoroughly sealed at the 

 top to prevent any water from entering. In some 

 camp stoves where intense heat is developed, 

 an air space between the fire-clay brick lining 



14 



