Paint stores carry phosphoric acid which is main ingredient in Naval Jelly which is diluted 3 to 5 times to keep the off gassed acid vapors tolerable.
Phosphoric will work much faster than Naval Jelly. DO NOT get it in your eyes. Wear chemical safe goggles.
If you use phosphoric you will want to be in open air and with a fan. If in garage you will not only need but WANT a respirator with acid gas cartridge.
Dan Bentler
