A method of limiting or reducing liquid and/or gas inflow through a porous matrix, comprising delivering to said porous matrix a coagulable polymer emulsion or colloid for contacting with at least one selected additive which interacts with said polymer emulsion or colloid to form a sealing barrier to reduce liquid and/or gas inflow through the porous matrix wherein said coagulable polymer emulsion or colloid contains at least one selected additive including one or a combination of radiation stabilisers to confer radiation resistance; and wherein said sealing barrier is formed by contacting said polymer emulsion or colloid with a further selected additive to cause coagulation of said polymer emulsion or colloid to form said sealing barrier. The sealing composition, which has low toxicity, preferably contains carbon black as radiation stabiliser conferring radiation resistance for the sealing barrier in the range 1 to 100 MRad.
