Classic/Antique Car Repair: Using Phosphoric Acid on Metal

Question
Good morning,

I am getting ready to use some phosphoric acid and "Rust Bullet" on various metal panels on my 1967 Ford F100 Pickup.  The phosphoric acid is called "Prep and Etch."

Here is my question: Should I wash off the acid (with water) after 30 minutes or so?  Or should I leave the phosphoric on the metal overnite and then wipe it off with a damp rag?

Thank you for your help.

John

Answer
The manufacturer of these products recommends washing the product off after 15 or 20 minutes. I have tried it both ways and find that the makers directions do the better job. Then if you are going to paint over it use the directions for the paint and the primer as well. I have never used Rust Bullet and their web sire recommends calling them for application information. But my base rule of thumb is to follow the makers instructions to the letter.