Does packing a cavity of a painfull tooth hurt?

I have a cavity that in honesty I should have had fixed a while ago but now I have cracked the tooth a little and my gum is inflamed. I have a dentist appointment on Tue but the pain is almost too much to take. A family friend (who has had his fair share of tooth problems) suggested I pack the cavity with salt and kill the nerve. The thing is, when it comes to teeth, I have such an unbelievably low threshold for pain, he say's it wont hurt but I can't think how it couldn't plus I think he is just trying to get me to do it. Has anyone any experience with this that can tell me honestly if it will hurt?