I just purchased a primed steel exterior door. I painted it with an exterior latex paint. The paint is peeling in the corners and around the trim. I did not sand it prior to painting because it was already primed. What do I do now? Should I have sanded the already primed door before painting? Now that it is painted and peelings, should I sand the whole door and then repaint?

It should have been degreased, very lightly sanded, cleaned again, then a quality ext. acrilic latex paint.
What color did you paint it?
Is it in direct sun?
Is there a full view storm door in front of it?

I wouldn't paint a metal door with anything other than an oil based paint.

The reason why is that latex paints are permeable to air and humidity, and that allows condensation to form on the metal despite it being coated with a latex primer and a latex paint. The result is that you can have rust forming on the door UNDER the latex paint.

Oil based paints are much less permeable to both air and humidity, and so they protect the metal better so that it doesn't rust.

Here, download and read this PDF:

http://www.paintquality.com/me...ducation/module6.pdf

Still, if the door came pre-primed from the factory, then one would presume it's ready for paint; whatever kind of paint the purchaser of the door choses to use on it. So, I have no explanation as to why your latex paint is peeling.

I disagree with sanding the factory primer, tho. The whole point behind sanding is to increase the surface area for the paint to stick to. Primer is rough so that it ALREADY has a large surface area for the paint to stick to. Sanding the primer is not going to increase the surface area, so from that perspective, I see no benefit whatsoever in doing it.

That is, this:
/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\
is rougher than this:
vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
but they both have the same surface area, and so a paint would stick equally well to both. Sanding the primer will make it rougher, but won't help the paint adhere any better.

What I would do is buy a roll of 2 inch wide regular masking tape and stick strips of that masking tape down on the latex paint near the peeling areas. Pull that masking tape of, thereby removing any latex paint that isn't sticking well. Pull off any latex paint that isn't putting up a fight to stay on.

Then clean the areas where the paint peeled off or pulled off with mineral spirits. Try to buy a bottle that says "Mineral Spirits", not one that says "Paint Thinner". Even though the two will normally be one and the same, as soon a manufacturer calls it "Paint Thinner" (instead of Mineral Spirits), he gets the artistic freedom to put whatever he wants in it that might help thin paint, including turpentine. Mineral Spirits will evaporate completely without leaving a residue, but you can't say that about "Paint Thinner" with certainty cuz of what might have been added to the mineral spirits it started out as.

Then, before you paint again, check the surfaces you're about to paint with your masking tape. If it pulls off easier than it should, then there's still something interfering with the adhesion of the tape, and whatever stuff that is will almost certainly interfere with the adhesion of the paint.

If the masking tape sticks OK, then I'd repaint the whole door with an oil based paint if oil based paints are still available for sale where you live. Otherwise, give it a second coat of any top quality latex.

This message has been edited. Last edited by: Nestor,

Next time you in Lowes or Home Depot take the time to read the lable on the steel doors.
All of them will say to paint with 100 % Acrilic latex within 24 hours of installing.
Not sure why, but that's what the manufactures all say.
Or look it up on line on there web sites under care.

A very light sanding is what we did with our factory primed, metal clad, wood core, doors and they have held up well for years, using exterior latex enamel.

Since the paint failure is around the edges and next to trim, I am wondering if just from packaging and handling finger oils or adhesive contaminates may have gotten on these areas prior to the painting? (since this is where they would be lifted and handled?) This is often another help with light sanding, it tends to remove this type of contaminate prior to painting.

For what it's worth, I repainted my exterior metal door a couple of years ago. The advice you've already received from Nestor, JoeCaption, and Conrad regarding cleaning up the door is important to complete prior to painting.
I primed and then used two coats of Sherwin Williams, High Gloss, Superpaint (100% Acrylic). It seems to be holding up well. I'm not sure if it matters, but my paint was white.

Good luck.