<p>Organosilane (OS) treatment has shown promise for mitigating geotechnical hazards such as frost heave by inducing hydrophobicity. However, its effectiveness under field-relevant in situ conditions, especially the influence of treatment method, is insufficiently understood. Motivated by a field implementation at the MnROAD Research Facility, where a spray application was adopted, this work investigates three soils when subjected to a spray treatment under laboratory conditions. Hydrophobicity was characterized by contact angle (CA) at varying depths within the soil profile and breakthrough pressure (BP) tests. Results showed that spray application led to hydrophobicity being confined to a finite near surface zone. Drying after treatment enhanced the measured CA response. Spray treatment led to relatively low BP values with the soil having the highest fine content, indicating that its fine pore structure restricted OS penetration and development of a hydrophobic barrier. Comparison with treatment where soils were compacted with OS showed that the latter had higher BP values. In this case, the soil with the largest fine content had the highest BP, indicating that once OS was distributed more uniformly, the fine pore structure became effective at restricting water entry. These findings demonstrate that the performance of hydrophobic soils depends strongly on treatment method and cannot be solely assessed based on surface properties.</p>