I had my outdoor metal grating painted two weeks ago with alkyd paint and it is still tacky. It is very humid here in Costa Rica and it rained a few days. Does paint sometimes take a very long time to dry? Does it ever not dry, just stay tacky forever?
Alkyd paints can take several days to dry to the touch during humid weather, but two weeks is an excessive amount of time. There is a possible cause; some manufactures still add Linseed oil to their oil based paints or have very slow drying paint to begin with. These paints can seem to take forever to dry. This might be the case for your metal grating. Another cause can be contaminates on the painted metal surfaces.
You have a couple of options to remedy this situation.
1) Do nothing and wait to see if the paint dries to the touch then hardens. After a couple of weeks the paint should have dried, perhaps all it needs is a few more days.
2) Repaint your metal grating. This time add some "hot" thinner to the paint to help with drying and curing. "Hot" thinner is any solvent that evaporates faster than regular mineral spirits. This can be Xylene or Lacquer thinner. Use small amounts in the paint and test this mixture on a piece of cardboard or wood. Wait until the next day and see if the paint is still tacky. Add more if necessary. Don't use denatured alcohol or acetone.
3) You can also try another brand of paint. It's possible what you are using isn't the best for your area.