Sandstone Subterranean Moisture Audit
1. Executive Summary & Sandstone Pathology
This building pathology audit was commissioned to evaluate subterranean damp ingress, surface efflorescence, and localized timber rot affecting the lower-ground cellar space of a historic Paddington terrace.
The perimeter walls are constructed of historic Sydney sandstone blocks bedded in soft lime mortars. Due to elevation raises in the rear courtyard, the external ground level sits 1.2m higher than the internal floor slab. Subterranean moisture is migrating laterally through the unprotected porous sandstone due to tanking failure and degraded external drainage channels. Fungal clusters (Cladosporium and Penicillium) were noted along structural floor timbers due to stagnant relative humidity.
2. Cellar Psychrometric Measurements (DampApp Pro™ Engine)
Atmospheric calculations indicate a localized moisture excess, showing a major vapor pressure discrepancy between the cellar air mass and upper floors.
| Atmospheric Parameter | Cellar Atmospheric State | Ground Floor Reference | Structural Safety Target |
|---|---|---|---|
| Dry-Bulb Temp | 17.8°C | 21.5°C | Target ≥ 18.0°C to offset dampness |
| Relative Humidity (RH) | 78.5% | 54.0% | Max 65% for structural safety |
| Vapor Pressure (VP) | 1.60 kPa | 1.38 kPa | Vapor pressure excess of +0.22 kPa |
| Vapor mixing ratio | 9.98 g/kg | 8.54 g/kg | Air mass dampness index |
| Fungal Germination Index | High Risk (0.83 aw) | Minimal (0.50 aw) | Fungal hazard threshold reached |
3. Localized Structural Defect Logging (AS 3660 / RICS Checklist)
The lower-ground masonry envelope has been scanned using non-destructive capacitance testing, establishing precise moisture bounds:
Porous sandstone blocks sitting below ground levels show high moisture saturation, with salt efflorescence destroying soft lime mortars. Active moisture ingress is bridging through plaster linings.
Structural Oregon floor joists adjacent to sandstone damp bridging show localized structural softening. Stagnant moisture and zero ventilation are initiating early wood decay.
4. Recommended Engineering Works
- Courtyard Excavation & Drainage Reinstatement: Excavate courtyard soils along the rear wall, clean sandstone surfaces, and install a subterranean agricultural drain backed by dimpled drainage membranes.
- Breathable Tanking Application: Apply a crystalline cementitious mineral tanking slurry to stone substrates internally to contain moisture migration while letting the soft lime masonry breathe.
- Positive Input Ventilation (PIV): Install a dry air input fan system to purge moisture excess from lower levels, reducing ambient RH below 60%.
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