Charak Samhita
तन्वालिप्तं न कुर्वीत संशुष्को ह्यापुटायते । न चौषधिरसो व्याधिं प्राप्नोत्यपि च शुष्यति ॥१०६॥
Thin lepa should not be applied because while drying develops cracks and medicinal property of lepa does not penetrates properly in the affected part as it dries up quickly.
english translation
tanvAliptaM na kurvIta saMzuSko hyApuTAyate । na cauSadhiraso vyAdhiM prApnotyapi ca zuSyati ॥106॥
hk transliteration by Sanscript