Masonry Magazine April 1977 Page. 12
MATERIAL SELECTION
Physical Properties. Several arguments are often advanced in favor of salvaged brick. Among these are:
1. Because brick are extremely durable, they can be salvaged and used again.
2. If the brick were satisfactory at the time they were first used, they are satisfactory now.
Both arguments are fallacious.
When brick are initially placed in contact with mortar, they absorb some water and some particles of cementitious materials. The initial rate of absorption (suction) is an important factor which greatly affects the bond between mortar and brick. Brick with extremely high or extremely low suctions do not develop good bond.
With salvaged brick, more factors influence bond. Pores in brick are filled with particles of lime, dirt, and other deleterious matter. Many bedding surfaces of salvaged brick will not be thoroughly clean, but will instead be covered with mortar. The bond between new mortar and old mortar is not very strong. If the original mortar bond was weak, the new bond will be adversely affected. That the bond to salvaged brick is considerably less than to similar new brick has been demonstrated many times by comparative tests (see Experimental Tests).
Most authorities agree that water penetration through masonry results from incompletely filled joints and incompletely bonded joints. That is, water penetrates through flaws in joints rather than directly through materials. Thus, masonry of salvaged brick, with its inferior mortar bond, is likely to be more susceptible to water penetration and weaker under lateral loading than similar masonry of new units. Its ultimate compressive strength will also be lower if salmon brick are present.
The durability of masonry depends upon the quality of materials and mortar bond. Generally, salmon brick are not durable when exposed to weathering. Yet, with the thinner masonry walls of today, brick are used primarily as a facing material. Thus, many salmon brick are eventually placed in exposed faces of salvaged-brick masonry. Even where solid brick walls are used, many salmons are likely to be exposed to weathering, because it is impossible to accurately sort and grade salvaged brick. With soft, highly absorptive salmon brick exposed to the weather, and with poor mortar bond permitting excessive water penetration, it is quite likely that masonry of salvaged brick will spall, flake, pit, and crack due to freezing in the presence of excessive moisture.
For a discussion of bond strength between mortar and new clay masonry units, see Technical Notes, No. 8, "Mortars for Clay Masonry."
A chimney of salvaged brick which has spalled considerably within a relatively short time after construction (Knoxville, Tennessee).
One common characteristic of most manufactured building materials is a reasonable degree of uniformity within a particular grade or within a given manufactured lot. Salvaged brick lack this distinction. Hard-burned and soft-burned brick, hopelessly mixed during wrecking operations, effectively create a material stockpile of two widely differing grades (see Fig. 1). A sample of the material will contain specimens of each grade. If tested for absorption or compressive strength, the sample will show widely diversified characteristics. The average absorption or strength will not approximate the true values for either grade, but will lie somewhere between. In effect, it is difficult to determine whether salvaged brick meet contemporary material specifications or building code requirements.
A close-up of a wall indicating the excessive spalling that is likely to occur where salvaged brick are exposed to weathering.
Esthetics. Salvaged brick may satisfy the desire for a rugged, colorful masonry surface. Architects often desire the extreme range of colors from dark red to the whites and grays of units still partially covered with mortar. But most frequently the