Stone and Masonry Types
Natural Stone Application – Introduction
Natural stone: obtained from rocks that constitute the earth’s crust.
Rock and stone are essentially the same materials, except that after the rock has been quarried, it is called stone.
Dimension stone: stone fabricated to required dimensions, texture, surface finish, and so on, and meets the requirements for durability, strong water absorption and the like.
The term includes stone cladding panels, veneer stone, counter- and table tops, wall copings, stair treads and risers. It specifically excludes broken or crushed stone.
Stone is a natural material, so its characteristics (properties and appearance) are inconsistent.
Types of Natural Building Stones
Granite
Takes an extremely good polish, commonly used in the exterior cladding of significant buildings.
Can contain 25% to 40% quartz and 3% to 10% mica; the remainder (50% or more) is feldspar.
Quartz is the strongest and more durable of the three minerals. It is more difficult to process (sawing, profiling, grinding).
It is not used where high strength or abrasion resistance is necessary, such as floors and stair treads.
Quartzite is a stone that is almost 100% quartz. It is commonly used as an aggregate to produce ultra-high-strength concretes.
Igneous rock strongest and densest.
Limestone consisting primarily of the carbonates of calcium and magnesium, with small amounts of clay, sand, and organic material such as seashells and other fossils.
generally nongranular, with a relatively uniform surface appearance, softer than both marble and granite hence easier to quarry, saw and
shape Color: white to gray.
Calcium carbonate reacts with acids. Most foods contain acids therefore, limestone is not used for kitchens or tabletops.
Several historic buildings with limestone facades have performed quite well in the absence of reactive atmosphere. Used commonly for concrete aggregate, sedimentary rock,
Marble
Geologically different from limestone because it is metamorphic rock.
Chemically similar to limestone but In fact marble is limestone, which under centuries of high pressure and heat in the earth’s crust changed from a sedimentary rock to metamorphic rock.
Because of pressure and heat, marble is stronger and denser than the original limestone takes a good polish.
Color: white to black, pink, and so on. Vulnerable to acid attack.
Travertine
sedimentary rock obtained from the sediments of limestone dissolved in spring-water.
Springwater (particularly hot springs) running over limestone deposits dissolved the limestone, which subsequently sedimented (deposited) in a nearby location.
Is a porous stone and slabs are pitted with voids.
They are softer.
They do not take the polish.
Denser varieties are referred as travertine marble.
used is building exteriors as masonry walls.
When used as a flooring material, the surface can collect dirt which requires greater maintenance.
Production of Finished Stone
Produced by stone fabricators from quarries in the form of large blocks.
Blocks are of irregular sizes (see figure 1).
Blocks are converted into slabs and other cross-sectional
profiles in stone fabrication plants.
The conversion is done by sawing the blocks-a process similar to sawing lumber, except that water is used continuously during the sawing process to keep the saw blades cool.
Natural building blocks of irregular sizes.
Sawing process of natural building blocks.
The saw uses a blade that can move in horizonlar and vertical direction.
Complex ornamental work requires hand tools
Ornamental works with natural building stones.
Finishes on Stone Slabs & Panels
The surface of stone slabs and panels can be finished in several ways.
This finish also effects the durability of stone.
The following are some of the commonly used finishes on stone slabs and panels.
Sawn finish:
If stone is not finished after sawing, it is called sawn
finish.
Saw marks are visible.
Honed finish:
When a sawn finish is ground smooth with an
abrasive material, a honed finish is obtained.
It requires repeated honing (grinding) with increasingly finer abrasives.
Water is used continiously during the process to control dust.
Polishing of surfaces.
Polished finish:
Polish finish is also honed but with a matt appearence.
It is obtained by grinding the stone surface beyond the honed finish with finer abrasives and finally buffing it with felt until the surface develops a sheen.
It brings out the colour of stone to its fullest extend by reflecting like a mirror.
Flame-cut finish:
Also known as “thermal finish”.
It is a rough finish obtained by torching the stone surface with a natural gas or oxyacetylene torch.
Before torching, the stone is wetted.
The heat from the torch expands the absorbed water into stream, which breaks loose surface particles in the stone, leaving behind a rough surface.
Ideal for floors subject to frequent wetting.
Bush hammered finish:
It is also a rough finish and is obtained by
hammering off the surface of stone with picks.
Split-face (cleft) finish:
Stone is split through one of its faces.
Sandblasted finish:
This process yields a rough surface.
Stone Selection
The selection of stone for a particular use is a function of several factors.
◦ Budget
◦ Aesthetics (color, pattern and surface appearence) are the two most
important factors to be considered for stone used in building interiors.
For exterior use, the history of performance of a stone in the local environment (durability) is obviously another important factor.
Generally the following properties are important:
Density
Water absorption
Compressive strength
Flexural strength (modulus of rupture)
Abrasion resistance
<h3>Common applications of selected stones.</h3>
Application
Exterior wall cladding Interior wall cladding Interior flooring
Stair treads and risers Kitchen counter top Bathroom counter top Wall copings and balusters Roofing
Commonly used stones
Granite, marble, limestone Granite, marble, limestone Granite, marble, slate Granite
Granite
Granite, marble
Granite, marble, limestone Slate
Bond Patterns in Stone Masonry Walls
In contemporary buildings, natural stone is generally used as thin slabs.
For exterior or interior wall cladding, slabs vary in thickness from 20
mm to 50 mm.
For flooring, slab thickness can be as low as 9.5 mm.
The thinner the stone, the smaller the size of slab in which it is available.
Stones used in exterior-wall veneers are generally 75 mm to 100 mm thick.Those used in load bearing stone walls are thicker.
In some cases, stones are so large and thick that they can not be laid by hand but require mechanical hoists.
Stone veneer and load-bearing stone walls are referred to as stone masonry to distinguish them from thin stone cladding.These walls are laid with mortar, stone by stone, in the same way as bricks.
Bond Patterns in Stone Masonry
Walls
Because natural stone is not available in uniform sizes as are bricks, the bond patterns in stone masonry walls are different from those used in bricks.
Two basic patterns used in stone masonry walls are
1. Rubble masonry
2. Ashlar masonry
Rubble masonry:
Made from stones whose sides are irregular (not at right angles to each other).
Rubble masonry is further subdivided as “random rubble” and “coursed rubble”.
Random rubble:The mortar joints are irregular.
A random rubble wall may consist either of stones obtained from the
quarries or rounded riverbed boulders.
Coursed rubble:The bed joints line up after every few pieces of stone
Therefore, the mason has to select the stones in the field (or shape them
using a pointed hammer) so that they fit in the available spaces.
Random rubble (irregular joints) and coursed rubble (regular joints) masonry walls.
Ashlar masonry:
The sides of the stones are dressed square (at right angles to each other).The front and back faces of the stone may, however, be dressed or undressed.
Like rubble masonry, ashlar masonry is also divided into 2:
1. random ashlar
2. coursed ashlar
