Abstract: The invention relates to a process for applying a liquid UV-curable primer sealant to natural stone tiles and related articles followed immediately by the exposure to a requisite amount of low intensity UVA-type UV radiation to partially cure the primer sealant. The partial curing, or pre-setting, of the primer sealant enables control of the ultimate depth of penetration of the primer sealer into the natural stone tiles and natural stone articles of which many examples are quite porous. Because the low level UV irradiation is instantaneous after the primer sealant application the level of primer sealant penetration into the natural stone surface is regulated. The pre-curing of the primer sealant is conducted to intentionally solidify or immobilize the sealant that has actually penetrated into the natural stone surface. The uppermost layers of the primer sealant are left in a semi-liquid or uncured state to allow for wetting and intermingling by the top sealant once it is applied.