VENEER (CAVITY WALL) MASONRY
A masonry veneer wall consists of masonry units, usually clay-based bricks (Locally referred to as R.O.K’s), installed on one or both sides of a structurally independent wall usually constructed of wood or masonry. In this context the brick masonry is primarily decorative, not structural. The brick veneer is generally connected to the structural wall by brick ties (metal ties that are attached to the structural wall, as well as the mortar joints of the brick veneer). There is typically an air gap between the brick veneer and the structural wall. As clay-based brick are usually not completely waterproof, the structural wall will often have a water-resistant surface (usually tar paper or bitumen) and weep holes can be left at the base of the brick veneer to drain moisture that accumulates inside the air gap. Concrete blocks, real and cultured stones, and veneer adobe are sometimes used in a very similar veneer fashion.
Most insulated buildings that utilize concrete block, brick, adobe, stone, veneers or some combination thereof feature interior insulation in the form of fiberglass batts between wooden wall studs or in the form of rigid insulation boards covered with plaster or drywall. In most climates this insulation is much more effective on the exterior of the wall, allowing the building interior to take advantage of the aforementioned thermal mass of the masonry. This technique does, however, require some sort of weather-resistant exterior surface over the insulation and, consequently, is generally more expensive.
DRY SET MASONRY
The strength of a masonry wall is not entirely dependent on the bond between the building material and the mortar; the friction between the interlocking blocks of masonry is often strong enough to provide a great deal of strength on its own. The blocks sometimes have grooves or other surface features added to enhance this interlocking, and some dry set masonry structures forgo mortar altogether.
Solid masonry, without steel reinforcement, tends to have very limited applications in modern wall construction. Such walls can, however, be quite economical and suitable in some applications; solid unreinforced masonry walls tend to be low and thick as a consequence of their lack of tensile strength.
Solid brickwork/masonry is made of two or more layers of bricks with the units running horizontally (called ‘stretcher’ bricks) bound together with bricks running transverse to the wall (called ‘header’ bricks). Each row of bricks is known as a course. The pattern of headers and stretchers employed gives rise to different bonds such as the common bond (with every sixth course composed of headers), the English bond, and the Flemish bond (with alternating stretcher and header bricks present on every course). Bonds can differ in strength and in insulating ability. Vertically staggered bonds tend to be somewhat stronger and less prone to major cracking than a non-staggered bond.
Uniformity and rusticity
The wide selection of brick styles and types generally available in industrialized nations allow much variety in the appearance of the final product. In buildings built during the 1950s-1970s, a high degree of uniformity of brick and accuracy in masonry was typical. In the period since then this style was thought to be too sterile, so attempts were made to emulate older, rougher work. Some brick surfaces (Face-brick) are made to look particularly rustic by including burnt bricks, which have a darker color or an irregular shape. Others may use antique salvage bricks, or new bricks may be artificially aged by applying various surface treatments, such as tumbling. The attempts at rusticity of the late 20th century have been carried forward by masons specializing in a free, artistic style, where the courses are intentionally not straight, instead weaving to form more organic impressions.
A serpentine wall (A.k.a a crinkle-crankle wall) is a brick wall that follows a serpentine path, rather than a straight line. This type of wall is more resistant to toppling than a straight wall; so much so that it may be made of a single thickness of unreinforced brick and so despite its longer length may be more economical than a straight wall.
CONCRETE BRICK & BLOCK MASONRY
Brick and block of cinder concrete (cinder blocks or breezeblocks), ordinary concrete (concrete blocks), or hollow tile are generically known as Concrete Masonry Units (CMUs). They usually are much larger than ordinary bricks and so are much faster to lay for a wall of a given size. Furthermore, cinder and concrete blocks typically have much lower water absorption rates than brick. They often are used as the structural core for veneered brick masonry, or are used alone for the walls of factories, garages and other industrial-style buildings where such appearance is acceptable or desirable. Such blocks often receive a stucco surface for decoration. Surface-bonding cement, which contains synthetic fibers for reinforcement, is sometimes used in this application and can impart extra strength to a block wall. Surface-bonding cement is often pre-coloured and can be stained or painted thus resulting in a finished stucco-like surface.
The primary structural advantage of concrete blocks in comparison to smaller clay-based bricks is that a CMU wall can be reinforced by filling the block voids with concrete with or without steel rebar. Generally, certain voids are designated for filling and reinforcement, particularly at corners, wall-ends, and openings while other voids are left empty. This increases wall strength and stability more economically than filling and reinforcing all voids. Typically, structures made of CMUs will have the top course of blocks in the walls filled with concrete and tied together with steel reinforcement to form a bond beam. Bond beams are often a requirement of modern building codes and controls. Another type of steel reinforcement, referred to as ladder-reinforcement, can also be embedded in horizontal mortar joints of concrete block walls. The introduction of steel reinforcement generally results in a CMU wall having much greater lateral and tensile strength than unreinforced walls.
CMUs can be manufactured to provide a variety of surface appearances. They can be colored during manufacturing or stained or painted after installation. They can be split as part of the manufacturing process, giving the blocks a rough face replicating the appearance of natural stone, such as brownstone. CMUs may also be scored, ribbed, sandblasted, polished, striated (raked or brushed), include decorative aggregates, be allowed to slump in a controlled fashion during curing, or include several of these techniques in their manufacture to provide a decorative appearance.
Glass brick, also known as glass block, is an architectural element made from glass. Glass bricks provide visual obscuration while admitting light. The glass block was originally developed in the early 1900s to provide natural light in manufacturing plants. Glass bricks are produced for both wall and floor applications. Glass blocks for use in floors are normally manufactured as a single solid piece, or as a hollow glass block with thicker side walls than the standard wall blocks. These blocks are normally cast into a reinforced concrete grid-work or set into a metal frame, allowing multiple units to be combined to span over openings in basements and roofs. Glass wall blocks should not be used in flooring applications. Hollow glass wall blocks are manufactured as two separate hemispheres and, whilst the glass is still molten, the two hemispheres are pressed together and annealed. The resulting glass blocks will have a partial vacuum at the hollow center.
SPECIALIST GLASS BLOCKS ARE PRODUCED FOR VARIOUS APPLICATIONS INCLUDING:
Bullet and vandal resistance: these blocks are generally solid glass or have very thick side walls similar to pavement blocks.
Fire resistance: fire resistance of varying degrees can be achieved by several methods. Standard production hollow wall block will offer little fire resistance; however, resistance is improved by utilizing specially produced hollow blocks with thicker sidewalls, or the inclusion of a special layer of fire resisting material between the two hemispheres of the block during manufacture. Some manufacturers of glass blocks have developed a method of bonding two glass blocks together with adhesive, producing blocks of up to 160 mm (6½”) thick with enhanced fire resistance. It is important that the block manufacturer’s recommendations are followed with regards to the installation of fire resisting glass block walls, as without special construction techniques, the wall will not achieve the desired fire resistance.
A recent innovation in the manufacture of glass blocks is the inclusion of argon gas within the hollow center of glass wall blocks. This advancement in production technique has resulted in a glass block which is able to offer significantly improved thermal insulation properties.
The International Standard for glass block is ISO TC 160/SG1. The Standards allow for variation in sizes and production irregularity. Blocks fall within three classifications; Class1, Class 2 and Class 3 with Class 1 being the highest and best rating with a maximum permissible deviation from designed size and rectangularity of 1 mm. Some hollow glass wall blocks are available in coloured variants. These coloured variants fall into two categories; those that are manufactured with coloured glass which are UV stable and can be used in the same locations as standard clear glass blocks. The other method by which coloured glass blocks are achieved is to inject a coloured material, dye or transparent paint into the hollow center of the blocks to form a permanent coating. This method of producing coloured blocks enables vibrant colours to be achieved which are not possible with coloured glass. The downside of this production method is that the coloured coating may not be UV stable and can fade in bright sunshine over time and therefore, may not be suitable for all locations.
Glass wall blocks are fixed together to form complete walls by several methods – the most common method of construction is to bed the blocks together in a Portland cement-based mortar with reinforcing rods of steel placed within the mortar as recommended by the project architect or block manufacturer.
Other methods of construction include several proprietary systems whereby the mortar is replaced by timber or PVC extrusions.
- Stone blocks used in masonry can be dressed or rough.
- Stone masonry utilizing dressed stones is known as ashlar masonry, whereas masonry using irregularly shaped stones is known as rubble masonry. Both rubble and ashlar masonry can be laid in coursed rows of even height through the careful selection or cutting of stones, but a great deal of stone masonry is un-coursed.
- Slip-form stonemasonry produces a hybrid wall of reinforced concrete with a rubble stone face.
- Natural stone veneers over CMU, cast-in-place, or tilt-up concrete walls are widely used to give the appearance of stone masonry.
- Sometimes river rock of smooth oval-shaped stones is used as a veneer. This type of material is not favored for solid masonry as it requires a great amount of mortar and can lack intrinsic structural strength.
- Manufactured-stone, or cultured stone, veneers are popular alternatives to natural stones.
- Attractive natural stone has become more expensive in many areas and in some areas is practically unavailable.
- Manufactured-stone veneers are typically made from concrete.
- Natural stones from quarries around the world are sampled and recreated using molds, aggregate, and colorfast pigments.
- To the casual observer there may be no visual difference between veneers of natural and manufactured stone.