hello all, im currently in the process of making a rather large head for a costume. i used a wire based home made frame, then putting peper mache over that

one question, when we made the paste we used the typical flour water salt, but we just used cold water, didnt read about boiling it till after.
what effect will this have?

secondly, we want this to be very sturdy and solid. do we just keep layering, or is there something like a spray hardener to help this along.