Ok you have sandpapered all the rust off, filled it with body filler and painted it and you are pleased with the rust removal repair. A couple of weeks later you walk out and notice a bubble on the paintwork in exactly the same place you did your repair and you have to start the rust removal repair all over again. How can this happen?
Well here is the main reason:
Preparation. This is the most important part of the rust removal process. If you don’t get this right then the rest of the repair will be a disaster. First you need to mask of the area that you do not want to be touched. This is tedious but if you want your repair to look professional then it is a must. Use masking tape and brown paper. Next grind or sandpaper the rust until you are back to shiny metal. Now this is where a lot of rust removal repairs go wrong. You need to be thorough.
Even if a black dot of rust left it will spread again like a cancer and you will eventually be back to where you were before. If you do find a black dot of rust you do not want to keep sanding this down as it you will wear the metal down to a point that it is so thin that it will be susceptible to rust again and defeats the whole purpose of the original rust removal.
One way I use to get rid of them is to drill a hole right through the centre of that pesky dot until it has disappeared. One or two tiny holes made by an 1/8th part drill will not cause any weakness to the panel and you can cover them with filler after a good brush with rust treatment, Any larger holes should be fixed with glass fibre and even larger holes will have to have a patch welded in. So if you sand the panel down and still get black patch say bigger than the size of your thumbnail stop there and seek professional advice, unless you have access to the correct body work equipment and know how to do the larger repair.
Assuming it is not a big job the next common mistake is using body filler. Even some professionals will fill the repair and and leave it overnight uncovered. In the morning they return to the job and spray it with primer then the top coat. Little do the know that body filler is porous and attracts moisture. It will go unseen and lie dormant until one fine day when the moisture will rise to the surface and raise its ugly head. You won’t see it until a bubble appears on your paintwork.
In order to prevent this happening, you must spray the body filler as soon as you can with a protective coat even of top coat and you can sand it off in the morning. I have even taken a welding torch over the top of my repair to heat the filler and eliminate any moisture. Do not take the chance that it is bone dry or you will live to regret it.
This is a very brief summary of how to remove rust and make a good long lasting rust repair. It is not a difficult repair and these tips could save you a ton of money in repair bills. If you want to know how to repair dents and other motoring money saving tips please visit my Auto Repair site.