24. ANNUAL REPORT 
from the outside—both present the same appearance, that of a mixture of 
plaster of a slightly pinkish color with crystallized selenite or gypsum. 
They do not appear to contain any sand. The mortar is easily reduced to 
fragments, but possesses a moderate degree of tenacity.” While the 
chemical analyses given by Mr. Wallace of both mortars do not parallel 
the usual Portland cement analyses, they do show that the ancient people 
knew how to manufacture the materials for a very durable mortar. An- 
other specimen, Mr. Wallace says, “was taken from the Pnyx, in Athens, 
the platform from which Demosthenes and Pericles delivered many of their 
orations. It has been long exposed to the action of the weather, is very 
hard, and of grayish white color.” 
While these specimens show the antiquity of mortar and how durable 
even a poor mortar may be, it is only within the last century and particu- 
larly the last decade that the high development of cement manufacture 
has brought into use mortars that are nearly perfect and almost indestruct- 
ible. 
THE ADVANTAGES OF CEMENT MORTAR OVER LIME MORTAR. 
The uniform bearing and equality of support in the bed of each block 
of stone aids in securing strong and durable masonry. Lime mortar has 
furnished a masonry construction which has endured for centuries under 
trying conditions, yet for modern requirements in large warehouses, sky- 
scraping office buildings and massive chimneys and bridge piers, a mortar 
which will more nearly equal in strength that of the building material 
used, is needed. Lime mortar simply furnishes a bed for the stone or 
brick, a bed which has but a fractional part of the crushing strength which 
stone or well made brick possess. With good cement mortar, however, 
a bed or joint 1s provided which continues to harden until frequently it 
will sustain greater strains without rupture than the body of the masonry 
itself can withstand. 
With lime mortar there are several weak characteristics, namely, lack 
of tensile or cohesive strength, lack of crushing strength, porosity, in- 
ability to harden under water, and the necessity for contact with air, that 
the mortar may receive sufficient carbonic acid to thoroughly set. 
Baker in his “Masonry Construction” gives the tensile strength of lime 
mortar of the proportions of 1 lime paste to 3 sand, at one year old, as 50 
pounds per square inch. ‘The present American Portland cements in mor- 
tars of the same proportions and age will run from 350 to 450 pounds per 
square inch. 
The crushing strength of mortars are about 8 to Io times their tensile 
strength and the same relative difference still exists between lime and 
Portland cement mortars, making the compression strength of Portland 
cement mortar from 3,500 to 4,500 pounds per square inch. 
The average tensile strength of 12 American Portland cements in 
mortars of I cement and 3 sand, one month old, tested at one laboratory, 
