CMU - Concrete Masonry Units

CMU Masonry

• CMUs are made from a stiff concrete mix pressed into metal molds.
• Steam curing in autoclaves accelerates curing.

CMU Classifications

• Heavier weight blocks are less expensive to manufacture, more durable, less moisture absorbent, have higher compressive strength, and provide better acoustical isolation.
• Lighter weight blocks are less expensive to transport and lay, have lower thermal conductivity, and have higher fire-resistance ratings.
• Light weight and medium weight CMUs are the most common.
• Measurement considerations depend on the number of joint widths in the dimension, which may be one more, the same, or one less than the number of blocks.

Laying CMU

• Corner leads are laid first.
• String lines and levels are used to maintain straight, plumb, and level walls.
• Joints are tooled, and the block face is cleaned as work progresses.
• Vertical reinforcing is placed in grouted cells.
• Lightweight horizontal reinforcing is placed in mortar joints.
• Vertical steel reinforcing is used in a fully grouted concrete block wall.
• Webs are partially sawn to make space for reinforcing bars.
• Specially shaped webs accommodate both vertical and horizontal reinforcing bars without modification.
• Structural steel, steel reinforced concrete block, and precast bond beam block shapes accommodate horizontal reinforcing low in the block profile.

Spanning Openings

• Steel reinforced concrete blocks feature a bond beam shape that accommodates horizontal reinforcing low in the block profile for tension resistance.
• Metal angles supporting the exterior brick wythe require flashing on top to intercept water in the cavity.

Decorative/Architectural CMU

• Split Face: Two or more blocks are cast as a single unit and split with knife-like blades during curing.
• Ribbed: Long lines are etched in.
• Ground: The block surface is ground smooth after curing to create a polished surface, which vary in color of aggregate and cement.
• Glazed blocks are colored.
• Glass blocks are individual glass units.
• Terra cotta are traditional cast, ornamental clay masonry units.

Types of Masonry Walls

• Solid walls lack a cavity, which can allow water to soak through and cause mold.
• Multiwythe walls have a continuous air space or cavity between wythes, acting as an internal drainage plane.
• Metal ties, which are corrosion resistant and adjustable, bond wythes across the cavity.
• The minimum cavity depth is 2 inches to allow space for masons to keep the cavity clear of mortar droppings.
• Flashing: An impermeable membrane (aluminum, stainless steel, or rubber) that redirects water to the exterior.
• Weep holes: Allow water to drain out of the wall.
• Dampproofing: Applied to the inner wythe to resist water penetration and act as an air barrier.
• Insulation can be added to the cavity.
• Mortar deflection material is inserted into the cavity to catch mortar droppings and prevent obstruction of weep holes.
• Composite walls can also be constructed of all one unit type.
• Metal reinforcing is more prevalent, and header units are uncommon in modern walls.
• Rows are courses, and the mortar joint is a bed joint.

Loadbearing Masonry Walls

• Carry gravity loads from floors and roofs, thus needing reinforcement via rebar for greater strength.
• The inner wythe is usually loadbearing, and the outer wythe is nonstructural.

Unreinforced Masonry (URM)

• Less helpful for seismic loads.
• Connecting floors to walls increases structural rigidity.
• Braces can be added to resist lateral forces.
• Gravity loads support floors and roofs.

Spanning Systems for Masonry Bearing Wall Construction

• Ordinary Construction: Traditionally interior wood frame, relates to IBC Type 3 construction, and any noncombustible exterior wall.
• IBC Type 4 Heavy Timber Construction.
• Steel and concrete floors and roofs may require added reinforcing or enlarged piers due to the point loads from open web steel joists.

Detailing Masonry Walls

• Through-wall flashing is located above interruptions in the cavity to intercept water within the wall.
• The backs and ends of flashings are turned up to direct captured water.

Materials for Flashing

• Sheet metal: Durable; stainless steel is the most expensive, copper is easy to form.
• Synthetic rubber membranes are self-adhering.
• Composite flashings consist of thin sheet metal laminated with heavy paper/plastic.
• Joints in metal flashing can be made watertight.

Weeps

• Thermal insulation uses rigid plastic foam within an Exterior Insulation and Finish System (EIFS).

Expansion and Contraction

• Masonry expands, and joints are added to avoid cracking from constraint.
• Joints are sealed at the surface.
• Some joint designs restrict out-of-plane movement between adjacent wall sections.
• Vertical expansion joints prevent cracking near windows.
• Joint sealant color is matched to brick, with sand cast into the sealant surface to imitate texture.
• Brick also expands with moisture.
• Soft joints for brick have internal flashing that does not project out, however the joint is not wide enough to accommodate expansion in the veneer.

Efflorescence

• White salt deposits on the surface of masonry occur when moisture carries dissolved salts to the surface as it evaporates.
• Efflorescence decreases over time but must be cleaned off.
• Deterioration of joints occur as they age.
• Repointing is a process to fix this deterioration.

Moisture Resistance

• Cavity wall construction and water-repellant coatings, which must be breathable to allow moisture to escape, aids resistance.
• Mortar and concrete for CMUs can be mixed with additives that increase their resistance to water intrusion.
• Protect mortar from freezing in cold weather, and similarly hot.

Brick Masonry

• Brick is one of the oldest and most durable building materials.
• Mortar cushions masonry units, provides uniform bearing, and seals joints between units to minimize air and water flow.
• Mortar is made from cement, sand, and water, and is important for a wall's appearance.

Portland Cement Lime Mortar

• Ingredients include portland cement, aggregate (sand), hydrated lime, and water.
• Hydrated lime allows for less water to be used to create more strength.
• Sand provides the basic structure to hardened mortar (one cubic foot of sand per cubic foot of mortar).
• Properties are defined by minimum strength, graded as MSNO (most to least strength).

Brick Raw Materials and Forming

• Made from natural clay, which is ground, screened, and mixed with water.
• Molded: Soft mud and dry mud processes.
• Extruded: Stiff mud process.

Brick Firing

• Formed bricks undergo drying and kiln-firing.
• Baked until dry, this process causes chemical transformation and takes 10-40 hours.
• Fly ash brick is made from fly ash (industrial waste product), sand, and water, plus formed by molded process

Brick Sizes and Shapes

• Brick is classified by size in inches, with modular size being standard and other sizes like engineer modular, closure modular, roman, and meridian being available.
• Specialty shapes are used to form arches, water tables, and other features.

Brick Solid vs Cored

• Solid: Less common now and frogged to reduce weight and prevent shifting on a wet mortar bed.
• Cored: Lighter in weight due to holes in the middle.

Brick Nomenclature

• Course: Row of bricks.
• Bed joint: Horizontal joint between courses.
• Head joint: Vertical joint between bricks in the same course.
• Wythe: One vertical stack of bricks.
• Collar joint: Vertical joint between wythes.

Brick Dimensioning and Laying

• Modular bricks mean wall dimensions should conform to the brick module to minimize cutting.
• Corner leads are constructed ahead of the rest of the wall.
• Levels and string lines are used to keep the wall straight and true.

Tooling

• Tooling creates joints between bricks and water is a concern, as it weakens mortar.
• Joint types include weathered, raked, stripped, struck, concave, vee, and flush.

Curtain Wall

• Shelf angles are installed on the structural frame.
• Soft joints (horizontal expansion) are maintained below shelf angles.
• Back up wall
• Cladding is laid up from a starting course at each shelf angle, with wire brick ties attached every six courses using two screws through the sheathing.
• Also includes waterproofing, brick ties, and scaffolding.

Brick Openings

• Use lintels (steel angle, stone, precast concrete, reinforced).
• Bricks can form arches, or corbelling.

Arch Types

• Segmental
• Tudor
• Roman
• Jack
• Elliptical
• Gothic

Brick Positions

• Rowlock: Brick laid on its face, end visible.
• Stretcher: Brick laid flat, face visible.
• Header: Brick laid flat, end visible.
• Soldier: Brick laid on end, face visible.
• Sailor: Like soldier but with broad side visible.

Brick Stacking

• Stretcher is a brick laid on its face, parallel to the wall, with its dimension horizontal.
• Header is a brick laid so as to bind two wythes together.

Brick Bonds

• Running bond: Alternating half steps, all runners.
• Common bond: Five or six rows of running bond, then a row of headers.
• English bond.
• Flemish bond has alternating runners and headers.
• Reinforced Brick Masonry (RBM) involves adding steel reinforcing to the masonry wall to increase its strength, especially in bending and shear.