Coating system

A system adapted for the application of a moisture-proof barrier to a substrate comprising:

• a first formulation containing between about 12 and about 32% by weight of a hydroxyl terminated butadiene polymer, between about 2 and about 14% by weight of a polyether triol having a hydroxyl number of between about 300 and about 500, between about 0.08 and about 0.8% by weight of an organo-mercury catalyst, between about 2 and about 10% by weight carbon black, between about 2 and about 24% by weight of a low oil absorbency silica, between about 0.1% and about 1% by weight of fumed silica as a suspending agent for the low oil absorbency silica, between about 0.08 and about 2% by weight of a molecular sieve dessicant, up to about 8% by weight of an organic solvent selected from the group consisting of aromatic solvents, ketones, esters and glycol ethers, and lecithin in an amount sufficient to provide a formulation viscosity of not greater than about 20,000 cps at 27.degree. C. and at which a reactive mixture prepared from said first formulation and a second formulation containing isocyanate groups can be readily sprayed onto a substrate;
• and
• a second formulation containing a urethane prepolymer derived from a polypropylene glycol ether polyol and toluene diisocyanate, containing between about 13 and 17% by weight free isocyanate groups;
• the two formulations of said system being adapted for mixing to provide a reactive mixture for application to said substrate;
• said system comprising defined relative proportions of said formulations so as to provide a molar ratio of at least about 1.1 isocyanate groups per hydroxyl group in said reactive mixture, said first and second formulations being adapted for mixing to form said reactive mixture at the site of the substrate to be coated.