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Bond strength and water leakage were determined for Types M, S, and N mortars joined to six different brick types. The air content, water retention, and flow rate were varied for each mortar-brick combination. It was found that air content, water retention, and compressive strength were inadequate indices of bond strength and water leakage. Yet these are the only properties specified in ASTM Specification for Mortar for Unit Masonry (C 270-84). A plea is made to add a bond strength requirement to present property requirements. The initial rate of absorption (IRA) of brick was found to be significant in predicting water leakage. Low IRA brick provided the highest probability of zero leakage.

The raw material is the major factor in limiting the speed of firing when using tunnel kilns of small cross section, such as the Prouty-type slab kiln. Raw materials vary greatly in the time required for water smoking, oxidation, and rapid shrinkage periods. The selection of materials that require small amounts of time can effect large reductions in firing time. Large.reductions in firing time can be accomplished for slowfiring materials through control of the grog particle size distribution or through the addition of other clays or shales to the material. Some reductions in firing time can be obtained through the elimination of hygroscopic water prior to firing and through apportioning the available firing time according to the needs of the raw material. Such scheduling permitted the firing of certain full-size brick in 81/4 hours.

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