Valve in block blew-leaking coolant

So my boyfriend rebuilt his 93\\\' civic hatchback, but when he put the engine back it wouldnt hold any coolant, and it was leaking by the water pump, so we replaced the water pump-still leaking. He says that there is a valve that is right on the inside of the water pump on the block that blew, he tried sealing it but nothing will work (used jb weld)-and hes freaking out pretty bad-worried that the car will blow if he trys to take it to a mechanic