Mortar joints in brick masonry wear
out. After 80 to 100 years, natural
weathering erodes the mortar, especially
soft lime mortar found in historic
masonry. Stress from structural
movement cracks the joints, letting in
water, and eventually freeze-thaw
cycles break down the mortar. You
cannot reverse the aging
process—only renew the outer layer
by repointing.
A repointing job should last for
another 100 years, but some jobs last
only a year or two. Why? Often, the
mortar is too strong. When it comes
to early brick masonry, stronger is not
necessarily better.
Cement vs. Lime
Repointing jobs on historic buildings
often fail because there are fundamental
differences between modern
and historic masonry.
Setting time. When a wall is laid
up with today's cement