If you remove the head then of course you replace the head gasket. Where can you get sodium silicate to fix a blown head gasket? Know that adding sodium silicate to an engine is only a temporary fix for a blown head gasket and will not permantly fix the problem. The only permanent fix is to replace the head gasket. I would never add any head gasket fix material to any engine.
A thermostat gasket is a gasket for a thermostat, a head gasket is a head gasket. The top part of the engine needs to be disassembled to repair the head gasket. You can find information on your specific car in your local library. You may even be able to access this online if the library has the databases available.
A blown gasket can be repaired by replacing the gasket...if you are talking about the head gasket, then you have to remove the cylinder head from the engine block and replace the gasket that is inbetween them. Cracked heads generally have to be replaced because they are made of aluminum which cannot be repaired permanently once it is cracked.