INFOPRO

Marble classification

This is a classification based on how solid the rock is, not its market value. The goal is to establish where a given type of marble can be used as a building material. It isn’t a hardness scale like the Mohs scale, but rather shows how, and by what methods, a marble needs to be processed before it can be used in a project.

Under this classification, there are 4 groups:

• Group A: marble with a compact structure, free of cracks and voids. Rocks in this category can be used both indoors and outdoors and don’t need reinforcing or filling. They behave uniformly during processing.

• Group B: similar to Group A, but with minor geological imperfections. They contain voids or cracks that, to be used properly, must be filled with polyester resins, epoxy fillers, and shellac. Standards require the resin to be applied without changing the marble’s color. Three procedures are defined:

• waxing – applying wax (different from polishing wax), for minor surface imperfections.

• bonding – applies to broken tiles, which are fitted back together and then secured with dowels, adhesive, or epoxy filler.

• filling – mainly uses synthetic resins.

• Group C: covers most of the more colorful rock types; these show structural flaws, holes, and separation lines. The appropriate technique is reinforcing the back of tiles, filling voids, and replacing defective tiles. With some exceptions, these marble categories are not recommended for outdoor use.

• Group D: the smallest group, containing varieties similar to Group C, but with more pronounced flaws requiring labor-intensive processing.

Some of PIATRAONLINE’s marble types are classified as follows:

• Thassos – Group A, needs no processing before use

• Tinos Green – Group B, minor processing if needed

• Emperador (Light and Dark), Crema Marfil, Forest Green, Nero Marquina – Group C, resin or back mesh applied where needed

All these procedures are carried out at the manufacturer, to ensure the tiles can be properly used in projects.

Classifying countertops by how well they can be cleaned of bacteria

Tests carried out on countertops made from different materials have shown that they respond differently to cleaning with commercial or household detergents.

Countertops made of granite, stainless steel, wood, concrete, ceramic, and plastic laminate were selected. Various contaminants (e.g. E. coli bacteria) were spread on the surface so it showed a moderate level of bacterial contamination.

When cleaned with a homemade detergent at a 10% concentration (one part 5%-strength food vinegar to nine parts water), the granite countertop, cleaned by scrubbing the surface, showed the greatest reduction in contamination and bacteria. Stainless steel followed (with a reduction rate 9 times lower), then concrete (15 times lower), then ceramic, wood, and plastic laminate.

These tests show that granite countertops don’t retain bacteria, and as such, represent the best material choice for work surfaces.

Thermal conductivity of natural stone-clad underfloor heating systems

Thermal conductivity measures the rate of heat transfer between two areas at different temperatures. This matters in various applications, such as underfloor heating for outdoor terraces or the boundary zone between a fireplace (stove) and a flammable exterior material. In such applications, conductivity, denoted k, must be calculated; it measures the amount of heat transferred through a section of material of a given thickness for each degree of temperature difference between the two environments. The higher the conductivity value, the more easily the material lets heat transfer through. If the value is low, the material doesn’t let heat transfer easily and heating happens slowly. For outdoor terraces, this can mean slow, sluggish surface de-icing, and for an indoor system, it can mean the room heats up slowly.

According to tests, the whole range of natural stone has good conductivity (with the best transfer rates for granite, marble, and sandstone), which makes it well suited for cladding over underfloor heating systems.

That said, for the boundary between hot zones and areas with fire risk, natural stone cladding is less recommended (limestone is a better fit).

Transporting slabs

For transport, slabs are placed vertically in wood or metal racks shaped like the letter “A.” Loading, unloading, road transport, and handling of slabs are all done with them in a vertical position, using specific gripping and transport systems.

Rack design doesn’t account for slab weight or for weight redistribution when one slab shifts or is removed. The result can be quite bad, since the slab can break or chip. That’s why securing slabs is necessary, and handling large tiles requires extra care.

When using other types of racks, individual compartments for slabs are recommended.

Each rack must be secured to the transport truck.

Both racks and their securing and anchoring systems should be checked periodically.