Comparative Screening of Oyster-Shell Lime and Silica Fume Formulations Containing Boiled Tung Oil for Potential Stone Heritage Crack Repair

Lime-based materials intended for stone crack repair in humid environments must balance liquid-water uptake, workability, mechanical performance, and moisture release. This study screens oyster-shell lime–silica fume–sodium silicate formulations containing 0%, 5%, 10%, and 15% boiled tung oil by mineral-binder mass. Mixing water varied concurrently, giving added-water-to-mineral-binder ratios of 0.500, 0.525, 0.550, and 0.575; the comparisons therefore do not isolate the effect of tung oil. Fresh, water-related, mechanical, and short-term cyclic responses were compared. Between the 0% and 15% formulations, reported 90-day water absorption decreased from 45.60% to 21.41%, initial contact angle increased from 54.32° to 94.38°, and capillary absorption coefficient decreased from 0.46 to 0.25 kg m−2 min−1/2. Flow spread decreased from 22.31 to 16.12 cm and setting was delayed. Strengths at 28 and 90 days decreased across the formulation sequence, whereas 7-day responses were nonmonotonic. Among the formulations tested under cyclic exposure, 5% (Si-T5) and 10% (Si-T10) showed different balances of residual strength and water uptake; both developed pronounced cracking by 30 freeze–thaw cycles. Specimen-level variability was unavailable, so numerical differences are descriptive and no statistical superiority or optimum is established. The study identifies formulation-dependent trade-offs without establishing an independent oil effect or field suitability.