How to quick fix a crack cylinder head for a car?

I've got a 3 cyl turbo daihatsu 1988 mdl had water problem and the mechanics changed the head gasket,but radiator still bubbling of air. So I was told it might have a hairline crack on the head.Is there a treatment for this? I was told there's a chemical treatment for this. If it is true can you tell me what to put in the radiator? thanks.