Ceramic Building Materials and Clay Manufacturing

Composition and Properties of Clay

The combination of clay and mullite is designed to resist temperatures up to 900 degrees. The composition includes alumina, silicas, iron oxide (red), white feldspar, and plastic clays. When processing, the addition of more water does not negatively impact quality; rather, the final quality depends on the raw materials and absorption rates (Apparent RPE area and temperature).

Additives and Processing

Oven fluxes are added to reduce the fusion temperature. Degreasers and burning additives are used to remove excess plasticity and ensure a uniform temperature throughout the mix. Additionally, plasticizing additives are utilized to refine the raw materials.

The Manufacturing Process

The production cycle involves several critical stages:

• Trituration and Homogenization: Breaking down and mixing materials.
• Weathering: To remove salts.
• Maturation: Soaking in water (H2O).
• Decay: To increase plasticity.
• Lamination: Preparing the layers for molding.

Molding Techniques

Molding of bricks can be done by hand (producing biscuits), which may result in uneven shapes, or through an extrusion press. Low plasticity clay is typically used for roofing tiles, while higher plasticity is required for drafts free of iron or oxide impurities. At 900 degrees, mullite decomposition occurs.

Firing and Vitrification

The firing (cocción) process begins at 700 degrees, with vitrification occurring at 1200 degrees. Products may undergo monococción (single-firing) or bicocción (double-firing) to achieve a vitrified finish.

Product Classification

Unranked or standard units include:

• RL-88 bricks (solid, single, or double perforated).
• Arabic flat tiles and vaults.
• Tubes, platelets, and stoneware tiles.

Quality Standards and Defects

Dimensional defects are categorized by visibility and impact:

• Class I: Visible at 0.5 meters; supports 7% and 1%.
• Class II: Surface flaws that affect aesthetic harmony.
• Class III: Not visible at 2 meters; includes tone defects without physicochemical changes in texture or water absorption.

Absorption Groups

Materials are classified by their water (H2O) absorption capacity:

• Group I: < 3%
• Group IIa: 3% – 6%
• Group IIb: 6% – 10%
• Group III: > 10%

Mechanical Resistance

Resistance to pressure and normal flexion is measured at 100 kg/cm² for standard use, 150 kg/cm² for posted use, and 200 kg/cm² for industrial use. Impact resistance is tested with a 1kg ball collision every 10 cm. Surface hardness and frost resistance (HELACO) must withstand 10 thermal shock cycles. Materials must resist changes in temperature, abrasion, adhesion, cracking, and detergents.

Specialized Brick Types

Thermoclay (often used in nasturtium/double-leaf walls) serves as a substitute for cheaper labor, utilizing porous polystyrene thin leaves. Bricks are classified as:

• Solid: Less than 10% perforation (30cm).
• Perforated (H): Holes drilled in the bed (tabla), header (testa), or edge (canto).
• Common (NV): Used for coating or non-facing work.
• Facing (V): Used for lining, requiring uniform dimensions in courses, headers, and stretchers (rope).

Hollow Bricks and Dimensions

Thick hollow bricks include the Rasilla (29x14x3, 24x11x2.5) and Hueco (24x11x4, 29x14x4.5). Double hollow bricks (5 to 6 holes) measure 29x14x9 or 24x11x8. Flatness on faces and maximum arrow deflection are strictly monitored. INCF stamping simplifies the reception of floor materials.

Ceramic Tiles and Finishes

Floor tiles with porosity < 3% are used as spares; porous adherent tiles are not always suitable for external use. According to molding methods, tiles are classified as Extruded (Type A) or Pressed (Type B):

• Low Absorption: < 5% (0.5% - 3% for Group I).
• Medium-High Absorption: Group IIa (3% - 6%), Group IIb (6% - 10%), and Group III (> 10%).

Suction and Surface Treatment

Suction (Espalter) should not be high on the face; it is measured by a 20-second drop test. Group III has high suction but should not leave a wet spot without suction. Finishes include enamel, engobe, unglazed (UGL), glazed (GL), clay, plaster, or workshop-polished sandstone.

Final Classifications

• Glazed Tile: E > 10%.
• Stoneware: E < 3% or 3% – 6%.
• Porcelain Stoneware (Gres Porcelánico): E < 0.5%.
• Other: Catalan tiles, rustic stoneware, and earthenware.