Table 6. Matrix of mortar moisture loss tests

Table 6. Matrix of mortar moisture loss tests.

Unit

Mortar

Air

Test

Unit

temperature

Unit

Mortar

type†

no.*

type

* Several of the initially planned tests were not performed (2, 5, 25, 26, 27).

† Unit properties are listed in Table 4.

The tests plotted in Figure 6 were all cured in

placed back into the bags and returned to the cool-

sealed bags in the cooling chamber, as were all

ing chamber.

tests conducted at 5C (41F) air temperatures. It is

Appendix A summarizes the results of the mor-

reasonable to assume that throughout the test the

tar moisture loss tests. Figures 6 through 10

mortar was losing moisture not only to the units in

present the significant findings from the tests.

which it was in direct contact, but also to the air

Effect of unit moisture. The effect of masonry unit

within the bag. The wetter the unit, the quicker the

moisture content on mortar moisture loss was

buildup of relative humidity within the bag,

measured using six different combinations of mor-

which reduced subsequent moisture loss from the

tar and unit temperature. In all six cases, mortar in

mortar to the humid air. Condensation within the

contact with the dry units exhibited a much

plastic bags during the tests supports this conten-

greater rate of moisture loss than with either the

tion. The effect of bagging the prisms can be seen

normal or the wet units. In addition, in all six cas-

in Figure 7. Due to handling, the bag surrounding

es, as expected, the wet units resulted in the lowest

one prism developed a hole that permitted mois-

rate of mortar moisture loss. While the moisture

ture within the bag to escape. The effect of the

loss of the mortar in contact with normal units was

vented bag resulted in a significant reduction in

always greater than that in contact with wet units

mortar moisture content in comparison with the

and lower than that in contact with dry units, the

mortar in the other prism. At the conclusion of the

relationships between them were not always con-

24-hr test, both prisms were removed from their

sistent. In two of the six cases, the mortar moisture

bags and returned to the cooling chamber. The rate

loss was approximately equal to the average of

of moisture loss from the mortar in the unvented

that with the dry and wet units, as exemplified in

prism then increased significantly, but the rate of

Figure 6a. In the other four cases, there was essen-

moisture loss from the mortar in the vented prism

tially no difference in mortar moisture loss be-

was virtually unaffected. Within several hours, the

tween the normal and the wet units, as shown in

moisture contents of both prisms stabilized at an

Figure 6b.

8