04-MASONRY Flashcards
content of MORTAR
basic constituents of modern masonry mortar:
PORTLAND CEMENT
LIME
SAND
WATER
BLEEDING in masonry
when water leaves the mortar and is deposited in a thin layer between the masonry unit and the mortar – when this happens it is said to FLOAT.
PROPERTIES OF HARDENED MORTAR
BOND STRENGTH DURABILITY COMPRESSIVE STRENGTH VOLUME CHANGE WATER TIGHTNESS RATE OF HARDENING MORTAR COLOR
SPALLING
when a masonry unit pop off a wall – often from the repeated cycles of freezing and thawing
EFFLORESCENCE
SUBFLORESCENCE / CRYPTOFLORESENCE
EFFLORESCENCE: water entering mortar then dissolving salts in mortar causing them to leach out onto surface of adj masonry - upon drying they crystallize and look unsightly but causes little harm
SUB/CRYPTOFLORESENCE: when the crystallization happen in a wall- considerable damage may result with a buildup of crystallization inside the wall and may cause spalling.
4 TYPES OF MORTAR MIXTURES
SAND-LIME (old rarely used)
PORTLAND CEMENT
PORTLAND CEMENT-LIME (ASTM C270)
MASONRY CEMENT (ASTM C70)
SAND-LIME
oldest mortar that use a mixture of lime, sand and water – hardens at a slow, variable rate, low compressive strength, and poor durability – many old bldgs have had this mortar dissolve away
advantage - high workability and high water retention, more flexible than portland cements
**seldom used except in rennovation work
PORTLAND CEMENT MORTARS
portland cements, sand and water
hardens quickly at a consistent rate and has high compressive strength, good durability when subjected to the freeze-thaw cycle
low workability and water retention are low
often used with architectural terra cotta (ceramic veneer) - not permitted in engineered unit masonry walls
PORTLAND CEMENT-LIME MORTARS
portland cement, lime, sand, and water
combines adv of portland cement and lime, produces most predictable mortars and grouts
the portland cement contributes to to high durability, high early strength, consistent rate of hardening and high compressive strength.
Lime adds workability, water retention, and plasticity
MASONRY CEMENT MORTARS
masonry cement, sand, and water
proprietary mixtures that combine various types of cement, natural cement, lime, diff slags
advantage: readily available, convenient to mix and good workability
ASTM C91 does not limit ingredients so performance is relatively unpredictable when compared to portland cement-lime mortars which adhere to ASTM C270 which dictates admixtures
**not recommended for reinforced masonry or in masonry subject to lateral forces/heavy loads
ASTM C270
recognized standard for mortar for unit masonry work and stone
lists required standards controlling the ingredients for mortar
ASTM C476
list controlling standards for grout ingredients for use in engineered masonry
MORTAR TYPES
M: high strength mortar greater durability than the others – 2500 psi (17.2 MPa)
S: medium-high strength recommended where bond and lateral strengths are more important than compression, max flexural strength – 1800 psi (12.4 MPa)
N: general purpose, medium-high strength for general use in exposed masonry abv grade where high compressive and lateral strengths are not required – 750 psi (5.2 MPa)
O: low-strength for general interior use 350 psi (2.4 MPa)
TUCKPOINTING
the refilling of an existing joint from which some of the mortar has been removed
should have same ingredients and mixture as original mortar
SOFT VS DRY PRESS PROCESS
SOFT MUD PROCESS: the oldest in which relatively moist clay (20-30 percent) is pressed into simple rect molds wither by hand or with molding machines, creates smooth dense surface known as water-struck if mold dusted with sand its sand-struck.
DRY-PRESS PROCESS: used for clays that shrink excessively during drying. Mixed minimally with water (10 percent) pressed into steel molds by a machine working at high pressure.
STIFF MUD PROCESS: most widely used today. Clay containing 12-15 percent water is passed thru a vacuum to remove pockets of air then extruded thru a rect die – bricks highly uniform in dim and shape – if variation desired here, bricks can be ‘TUMBLED’.
