Testing & Benchmarking

Water Absorption

Measures how much water a fired ceramic body absorbs when fully saturated. For terracotta cladding this is a proxy for vitrification — too high means underfired or porous; too low means overcured. Terreal specifies 6–9%, matching Group AIIb in EN 14411.

Equipment

• Kitchen or lab scale accurate to 0.1 g
• Oven (110°C or higher)
• Pot, water, heat source for boiling

Procedure

1. Dry sample in oven at 110°C to constant weight (≥24 h). Record dry weight W_d.
2. Boil in water for 2 hours, fully submerged.
3. Cool in water for 4 hours.
4. Remove, wipe surface dry quickly, weigh immediately. Record saturated weight W_s.
5. Water absorption % = (W_s − W_d) / W_d × 100.

Can be done with a kitchen scale and a pot — no specialist equipment required for screening.

Modulus of Rupture (MOR)

Three-point bend test. The primary structural qualification for cladding panels. Brittle ceramic fracture under flexural load. EN 14411 requires ≥18 MPa minimum individual and ≥22 MPa mean for Group AIIb tiles. Terreal's spec of >15 MPa is a conservative minimum target.

Equipment

• Three-point bend fixture (two support rollers + one loading roller)
• Load cell or calibrated weight + lever arm for improvised rig
• For formal certification: accredited materials testing lab (Zwick, Instron, etc.)
• Digital calipers (measure sample dimensions)

Procedure

1. Measure sample width b and thickness d at the center (mm).
2. Set span length L (typically 10× thickness). Record L.
3. Apply load at center at a constant rate (1 mm/min) until fracture. Record force at break F (N).
4. MOR (MPa) = 3FL / 2bd²
5. Test ≥5 samples; report mean and minimum.

Porosity (Archimedes Method)

Measures open porosity — the fraction of the sample volume that is pore space connected to the surface. Key for understanding how much further sintering can reduce absorption. Complements water absorption data.

Equipment

• Analytical scale accurate to 0.001 g with suspension hook
• Beaker of distilled water, wire hanger rig
• Vacuum pump (optional, for better pore saturation)

Procedure

1. Dry sample at 110°C to constant weight. Record W_dry.
2. Boil in water 2 h (or vacuum saturate: 30 min at <10 mbar, then release to atmospheric). Cool in water.
3. Weigh sample suspended in water (wire hanger). Record W_sub.
4. Remove, wipe, weigh in air immediately. Record W_sat.
5. Open porosity % = (W_sat − W_dry) / (W_sat − W_sub) × 100.
6. Bulk density (g/cm³) = W_dry / (W_sat − W_sub).

Dimensional Shrinkage

Tracks shrinkage from green → dried → sintered. Uniformity matters more than absolute value — consistent shrinkage can be compensated in the mold design. Inconsistent shrinkage causes warping and dimensional variation between units.

Equipment

• Digital calipers (0.01 mm resolution)
• Reference marks scribed on green body before drying/firing

Procedure

1. Mark reference points on the green body after demolding. Measure length, width, and thickness. Record.
2. After drying to constant weight, re-measure same dimensions.
3. After sintering, re-measure.
4. Shrinkage % = (initial − final) / initial × 100 for each stage.
5. Track across multiple samples from the same batch to measure consistency.

Compressive Strength

Measures resistance to compressive load. For facade cladding, MOR (flexural) is the primary structural test; compressive strength is secondary. Useful as a process quality metric — compressive strength correlates with sintering density and binder burnout quality.

Equipment

• Compression testing machine (Instron or equivalent)
• Parallel-ground sample faces (±0.05 mm parallelism)

Procedure

1. Cut or grind sample to a regular geometry (cube or cylinder). Record dimensions.
2. Load at constant displacement rate (0.5 mm/min) until fracture. Record peak force F.
3. Compressive strength (MPa) = F / cross-sectional area.

Frost Resistance

Required for any exterior cladding in climates with freeze-thaw cycles. Tests whether water trapped in pores expands on freezing without cracking the ceramic body. Formally requires a programmable climate chamber; a simplified version can be done with a domestic freezer.

Equipment

• Programmable climate chamber (formal) or domestic freezer + water bath (screening)
• Visual inspection + scale for weight loss measurement

Procedure (simplified screening)

1. Saturate sample in water for 24 h. Record wet weight.
2. Freeze at −15°C for 6 h (sample still wet).
3. Thaw in water at room temperature for 6 h.
4. Repeat for 50 cycles minimum.
5. Inspect after every 10 cycles for visible cracking, spalling, or surface flaking.
6. Record weight loss after final cycle (fail if >1% mass loss or visible damage).

Formal test per EN ISO 10545-12 requires −5°C → +5°C cycling with controlled ramp rates.

Acid Rain Resistance

Tests resistance to acid-driven surface degradation over decades of outdoor exposure. Natural acid rain is pH 4–5. Accelerated testing uses pH 1–2 H₂SO₄/HNO₃ (2:1 molar ratio, matching acid rain chemistry) for 24–96 h to simulate years of exposure.

Equipment

• Dilute H₂SO₄ and HNO₃ (or citric acid for a safer proxy)
• pH meter or pH strips
• Scale (0.01 g), container, tongs (acid-safe gloves required)

Procedure (accelerated, lab-safe version)

1. Dry sample to constant weight. Record W_initial.
2. Prepare pH 1–2 solution: dilute H₂SO₄/HNO₃ 2:1 molar, or 5% citric acid (pH ≈ 2) as a safer proxy.
3. Submerge sample fully. Soak for 24–96 h at room temperature.
4. Remove, rinse in deionized water, dry at 110°C to constant weight. Record W_final.
5. Mass loss % = (W_initial − W_final) / W_initial × 100.
6. Inspect surface visually for etching, pitting, or glaze loss.

5% citric acid (kitchen-safe) at pH ≈ 2 is a practical substitute for H₂SO₄/HNO₃ for initial screening. Full protocol requires fume hood and acid-safe PPE.

Thermal Shock Resistance

Tests resistance to rapid temperature changes — relevant for dark-glazed or south-facing facades where solar heating can cause significant thermal gradients during rain events.

Equipment

• Oven capable of 145°C
• Container of room-temperature water (15–25°C)
• Tongs, gloves

Procedure

1. Heat sample in oven at 145°C for 30 minutes.
2. Remove and immediately immerse in water at 15–25°C.
3. Remove from water and dry. Inspect for cracks using ink penetrant (apply ink, wipe, cracks retain ink).
4. Repeat for 10 cycles.
5. Pass: no cracking or delamination visible after all 10 cycles.

UV Resistance

Tests resistance to UV-driven surface degradation — relevant for outdoor facade cladding exposed to years of solar UV. Formal standards use xenon arc (ISO 4892-3) or fluorescent UV lamps (ASTM G154); a domestic UV nail curing lamp (~36W, 365nm) is a practical substitute for initial screening.

Equipment

• UV lamp — 365nm or broad-spectrum (e.g. blacklight or UV nail curing lamp, ~36W)
• Timer, scale (0.1 g), digital calipers
• Camera for surface photography
• Reference colour record (RAL chart or written description)

Procedure

1. Dry sample to constant weight. Photograph surface and record colour (RAL or visual note).
2. Expose sample to UV lamp at ~15–30cm distance for 100–200h. Flip halfway for even exposure.
3. After exposure: photograph, record any visible discolouration, chalking, or surface changes.
4. Weigh — record any mass loss.
5. Optionally: perform MOR test on exposed vs unexposed samples to measure strength retention.
6. Pass: no visible surface degradation; mass loss <0.5%; MOR retention >90% of unexposed value.

A domestic UV nail curing lamp (~36W, 365nm) is a practical substitute for formal weathering chambers for initial screening. ISO 4892-3 specifies xenon arc lamp; ASTM G154 uses fluorescent UV.