do you need to ground this paint to have an effect? what happens if you don't ground it?

This paint needs to be grounded for safety reasons due to the surface electrical conductivity. Also, grounding the paint will reduce the low-frequency electrical fields. If you painted a wall that covers electrical components and did not ground the paint, if you drilled into the wall and contacted a wire you could be harmed. Hope this helps. Regards, EMR Shielding Solutions Inc.

Can this be shipped to California?

Hello, Good afternoon. Thank you for reaching out to us. This can be shipped to California. Please let us know if you have further questions.

Would this be good in electrical cavities of Musical instruments?

Hello, I have confirmed with the manufacturer that this type of application is acceptable. Thank you.

Thank you very much. Do I need any of the optional add-ons?

You can use the EB2 Conductive Tape to increase the conductivity across the paint and use either GW Interior Grounding Kit or GE Exterior Grounding Kit to ground the paint.