I have a metal back door. It is in good shape except a spot where the dogs continually push it open - it has a rust spot, I guess from their wet noses. At any rate, I have tried a sander on it (the metal is all bumpy) and paint, but the rusty bumps keep coming up through the paint. My question is this - is there some sort of sander for metal that might get that spot off? I am trying to sell my house and would prefer not to replace the door. Thank you for any ideas.

 

I suspect your problem is with the paint and not the door or rust. Latex paint/primer will not hold back rust. Oil base is better [or any solvent based coating] You need to sand down the rust and coat it with a solvent based primer - preferably a rust inhibitive primer. With 1-2 coats of a solvent based primer you should be able to top coat with latex and not have any problems.

 

If you're hand-sanding you'll be at it a really long time. The easiest way to sand doors like this (assuming the rust is not on a contoured/decorative accent) is to get a random orbital sander. Don't get the 1/4 sheet palm models, go for the models that use the round, hook-and-loop sanding discs. I picked up a Skil sander from wally-world for around $40, and it's still going strong.

Use 50 to 80 grit paper, (I'd start with 80 or even 100 grit until you become familiar with how much material it removes and how fast.) You'll probably go through several sanding discs, so the larger packs (i.e. 15 discs) are usually worth the extra money.

If you're no stranger to power tools and have a knack for quickly developing the skills and finesse needed... and, like me, your eyes are always drawn to the biggest/most aggressive models, you could get a 4-1/2" angle grinder. A low-end DeWalt can be had for about $50. Get a sanding-disc attachment and some sanding discs designed for the high RPMs of a grinder.

The grinder will make quick work of any "bumps" and deeply rusted metal, but it'll sand a hole in your door if you're not careful.

I use both the sander and the grinder, but you should probably stick to the sander; it's more user-friendly, much safer, and it's ready to go out of the box, no need to buy separate attachments (less $).

Also, don't forget an appropriate dust mask/respirator and safety glasses!

Sorry for such a wordy post, hope it helps.

~Jeffrey

P.S. After you take care of the rust, follow Marksr's advice about the paint. If you don't, all of the above won't do you much good.