- Geological Classification
- Color and Veining
- Product Sampling
- Job Inspections
- Damp Proofing
The rock forming the earth’s crust falls into three generic groups: igneous, sedimentary and metamorphic.
Heat, pressure, and chemical reactions may change either igneous or sedimentary rock into metamorphic rock, meaning “changed in form.” Lime stones usually have been classed as igneous rocks derived from molten masses or magmas, but there is wide evidence that the origin of some lime stones may be attributed to regional metamorphism or preexisting rocks, rearrangement and recrystallization taking place without a liquid or molten stage.
Dimension Limestone is divided into three sub classifications that describe their densities in approximate ranges, as follows:
- Low Density – Limestone having a density ranging from 110 through 135 lb/ft 3rd (1760 through 2160 kg/m 3rd)
- Medium Density – Limestone having a density greater than 135 and not greater than 160 lb/ft 3rd (2160 through 2560 kg/m 3rd )
- High Density – Limestone having a density greater than 160 lb/ft 3rd (2560 kg/m 3rd)
Color and Veining
The color, veining, clouds, mottling, and shadings in limestone are caused by substances included in minor amounts during formation. Most of these dark materials are found between calcite crystals or the shell materials, and some shells and calcite crystals are darker then others. Iron oxides make the pinks, yellows, browns, and reds. Most grays, blue-grays, and blacks are of bituminous origin.
The term “texture,” as applied to limestone, means size, degree of uniformity, and arrangement of constituent minerals.
Limestone contains a number of distinguishable natural characteristics, including calcite streaks or spots, fossils or shell formations, pit holes, reedy formations, open texture streaks, honeycomb formations, iron spots, travertine like formations and grain formation changes. One or a combination of these characteristics will affect the texture.
Limestone surfaces may be finished in a number of ways. Typical finishes are:
- Polished – A glossy surface which brings out the full color and character of the limestone.
- Honed – A satin smooth surface with little or no gloss.
- Smooth – Smooth finish, with minimum of surface interruption.
- Plucked – A rough texture.
- Abrasive – A flat, non-reflective surface.
- Sawn – A comparatively rough surface; can be chat, shot, sand or diamond sawn.
- Other finishes such as machine-tooled or thermal are available.
Standard thickness for limestone are generally ¾ inch, 1-1/4 inch, 1-1/2 inches, 2 inches, 2-1/4 inches, 2-1/2 inches, 3 inches, 3-1/2 inches and 4 inches.
Cutting can be made to exact metric measurements through conversion of English values to metric equivalents. Note that as limestone is cut thinner its tensile strength is diminished.
Limestone is a product of nature of which many varieties are available, each possessing varying characteristics. Little can be done to alter the condition in which nature presents these varieties to us. Therefore, size may become a limiting factor to consider in the selection of a particular limestone.
Consultation for specific size information for a particular stone is recommended. A jointing scheme which permits the use of smaller sizes of limestone may greatly facilitate selection and delivery.
Because of the many varieties in types of limestone, it is recommended that the limestone quarries or fabricator be contacted regarding size and thickness tolerances.
Limestone is formed by nature; thus, there are variations in the tonal qualities of the stones. However, it is these natural variations that make limestone unique, valuable, and highly desirable. Because of these variations, selection of a limestone should never be made on the basis of one sample only. It is recommended that selection be based on viewing sufficient samples to show the complete range of color of desired stone.
Misunderstandings, misinterpretations, shoddy workmanship and deficient materials may all lead to impasses that seemingly cannot be resolved by reasonable discussion. Upon application to the MIA office, and completion of the proper forms, a qualified inspector(s) will be assigned to visit the job site, review plans, specifications and the approved samples, and record an opinion. A written report will be issued by the MIA office. Inspection fees vary with the size and value of the project.
Many limestone have absorption rates which will cause “bleeding” of setting or joint materials. If unsure, the limestone should be tested for tolerance of the setting material. If necessary, edges and back faces must be damp proofed with materials that will bond with the setting/jointing material, but not cause bleeding.