Techniques > Briefs
> Repointing Mortar Joints
The Russack System for Brick & Mortar Description...include
drawing locating areas to be pointed
Portions of the building may have been repointed in
photo process of inspecting, samling
Visually Examining the Mortar and the Masonry Units
A simple in-situ comparison will help determine the hardness
and condition of the mortar and the masonry units. Begin by scraping
the mortar with a screwdriver, and gradually tapping harder with
a cold chisel and mason's hammer. Masonry units can be tested
in the same way beginning, even more gently, by scraping with
a fingernail. This relative analysis which is derived from the
10-point hardness scale used to describe minerals, provides a
good starting point for selection of an appropriate mortar. It
is described more fully in "The Russack System for Brick
& Mortar Description" referenced in Selected Reading
at the end of this Brief.
Mortar samples should be chosen carefully, and picked from a
variety of locations on the building to find unweathered mortar,
if possible. Portions of the building may have been repointed
in the past while other areas may be subject to conditions
causing unusual deterioration. There may be several colors of
mortar dating from different construction periods or sand used
from different sources during the initial construction. Any of
these situations can give false readings to the visual or physical
characteristics required for the new mortar. Variations should
be noted which may require developing more than one mix.
- Remove with a chisel and hammer three or four unweathered
samples of the mortar to be matched from several locations
on the building. (Set the largest sample aside this
will be used later for comparison with the repointing mortar).
Removing a full representation of samples will allow selection
of a "mean" or average mortar sample.
- Mash the remaining samples with a wooden mallet, or hammer
if necessary, until they are separated into their constituent
parts. There should be a good handful of the material.
- Examine the powdered portion the lime and/or cement
matrix of the mortar. Most particularly, note the color.
There is a tendency to think of historic mortars as having
white binders, but grey portland cement was available by the
last quarter of the 19th century, and traditional limes were
also sometimes grey. Thus, in some instances, the natural
color of the historic binder may be grey, rather than white.
The mortar may also have been tinted to create a colored mortar,
and this color should be identified at this point.
- Carefully blow away the powdery material (the lime
and/or cement matrix which bound the mortar together).
- With a low power (10 power) magnifying glass, examine
the remaining sand and other materials such as lumps of lime
- Note and record the wide range of color as well as the
varying sizes of the individual grains of sand, impurities,
or other materials.