3.3.1.1
Mortar Analysis
Existing original historic mortar shall be analyzed before repointing in
order to provide a match with the new repointing mortar. Historic mortars
are usually softer than newer mortars, often using lime as a binder rather
than cement. Lime for repointing mortar shall conform to ASTM C 207, Type
S, unless otherwise specified. Full laboratory analysis of the existing
mortar shall conform to ASTM C 1324. Field analysis of the existing mortar
shall be as specified below.
3.3.1.2
Taking and Preparation of Samples
Samples of unweathered original historic mortar shall be taken and analyzed
in order to match the new mortar to be used for repointing. Samples of
each different type of mortar in the structure shall be taken and analyzed.
Three or four samples of each type of mortar to be matched shall be
removed with a hand chisel from several locations on the building. The
largest sample shall be set aside for comparison with the repointing
mortar. The remaining samples shall be broken apart with a wooden mallet,
powdering them into their constituent parts.
3.3.1.3
Binder Analysis
A part of the sample shall be stirred into diluted hydrochloric acid. If a
vigorous chemical reaction (bubbling) occurs and most of the binder
disappears, leaving clean aggregate, the binder was lime. A portland
cement binder will result in a murky liquid and will dissolve very slowly
over several days.
3.3.1.4
Aggregate Analysis
Aggregate of the mortar sample shall be separated from the binder. This
shall be accomplished by taking the crushed mortar sample and either gently
blowing away the fine binder material, placing the crushed sample in a
centrifuge, or chemically separating the aggregate from the binder. The
separated aggregate shall be rinsed clean with water and dried. The
aggregate shall be examined with a magnifying glass, and the component
materials shall be recorded as to range of materials, sizes, colors, as
well as the presence of other materials.
3.3.2
Mechanical Repair
Original historic masonry materials shall be repaired or replaced only if
surfaces are extensively deteriorated (surface missing to a depth of 100 mm
4 inches or more) or are threatening the safety of the structure or
individuals. Deteriorated surfaces shall be removed and repaired or
replaced only upon approval. Repairs and replacements shall match the
materials, colors, and finish of the existing historic masonry as closely
as possible.
3.3.2.1
Areas To Be Removed
Unsound, weak, or damaged masonry and mortar shall be removed in areas as
indicated. Loose particles, laitance, spalling, cracked, or debonded
masonry and mortar and foreign materials shall be removed with hand tools
unless otherwise noted. Surfaces prepared for repair shall be cleaned free
of dust, dirt, masonry chips, oil or other contaminants, rinsed with water,
and dried before repair work is begun. Surfaces of the structure, and
surfaces adjacent to the work area shall be protected from damage which may
SECTION 04900
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