There is disclosed a method of producing a pre-mixed porous polymeric composition comprising the steps of: encapsulating granules of rubber to isolate any contained curing agent or water; mixing a moisture curing quasi-prepolymer or prepolymer with the encapsulated granules, in a low moisture or moisture free environment; depositing the mixture, in a low moisture or moisture free environment, into containers which are impermeable to water vapour or which have a low water transmission rate; storing the mixture containing containers for later use; and when required, and without further mixing, applying the composition to a suitable sub-base and allowing the composition to polymerise by reaction with water.