Mortars
Used to bond the units together into a complete assembly. Provides assembly with shear strength, particularly parallel to wall. Permits some movement between units. Seals irregularities of assembly. See Masonry Council for supplemental information.
- Basic ingredients
- Cements: contribute to mortar's durability and high early strength. There are three types permitted by UBC:
- Portland Cement
- most commonly used.
- limited to types I, II, or III.
- Masonry Cement
- a proprietary blend of portland cement and plasticizers, ingredients not known.
- not prohibited in seismic zones 2, 3, and 4.
- Mortar Cement
- also proprietary.
- portland cement based materials.
- higher quality than masonry cements.
- may be used in all seismic zones.
- Portland Cement
- Cements: contribute to mortar's durability and high early strength. There are three types permitted by UBC:
- Hydrated lime: contributes to mortar's workability, water retentivity, and elasticity.
- Mortar sand: acts as a filler and contributes to strength.
- Water:
- used to create a plastic, workable mortar.
- is required to hydrate the cement.
- must be clean.
- avoid water with soluble salts such as potassium and sodium sulfates, which can contribute to efflorescence.
- efflorescence = unsightly deposit of salts on the surface of the assembly.
- Admixtures:
- use with caution: can effect bond between units and mortar, can contribute to efflorescence and steel corrosion.
- accelerators and retarders: effecting the set and stiffness of the mortar.
- Color:
- mineral oxides.
- The proportions of mortar ingredients must conform to UBC ' 97 Table 21-A, unless conforming to UBC ' 97 2103.3.2
- Originally 5 types:
M A S O N W O R K ß ß ß ß ß Strongest Weakest
- UBC no longer recognizes K.
- Mortar type and use:
Type Use M high compressive loads, severe frost action, high lateral loads, structures below or against grade. S structures requiring high bond strength and subjected to compressive and lateral loads. N general use above grade. O non-load bearing walls and partitions not subjected to weathering.
- Selection guide:
Location Building Element Recommended Exterior, above grade Load-bearing wall N Non-load bearing wall O Parapet wall N Exterior, at or below grade Foundation wall, retaining wall, manholes S Interior Load-bearing N Non load-bearing O
- Good water rententivity: prevents rapid loss of mixing water to absorptive units and air.
- Prevent water bleed out.
- Prevent stiffening of mortar prior to laying units.
- Retain enough water for hydration of cement Þ proper bonding of units.
- Bond: most critical property of mortar effecting long term strength of assembly and serviceability.
- Water tightness.
- Resist tensile stresses (shrinkage).
- Masonry assembly strength in shear and bending is a function of bond strength.
- Workmanhip is critical in bonding.
- Mortar compressive strength
- A Q.C. measure.
- A minimum strength is required for assembly strength and durability.
- But it has little influence on overall assembly compression strength.
- Workability is more important than compression strength.
- Better workability Þ more deformable Þ better able to accomodate differential movements.
- Workability: as wet as possible, yet stiff enough to support the blocks.
- Slump does not provide a good measure of this.
- Mason's judgement still the best.
- Tempering: adding water to restore a stiff mortar to a better consistency - should not retemper if mortar has begun to set and has hardened enough to become harsh. Use within 2 1/2 hours.
- Standard joint thickness = 3/8"
- Classes:
- Cut - cut flush with wall with trowel.
- Troweled - excess mortar is cut and finished with trowel.
- Tooled - special tool to compress and shape mortar.
- Some joints provide poor weather resistance: avoid weather, squeezed, raked and struck (see page 67 in Schneider and Dickey).
- Basic terms:
