I find that while a nice finish can be acheived on aluminum siding, or any metal surface , using quality rollers and good, leveling paint, there is really no comparison to a spray finish on metal. We have painted aprroximately 60 homes with aluminum siding to date, all using airless spray equipment, fine finish tips, extensive masking techniques and SW Super Paint (which is not too thick, like Duration) . We actually learned from the pros, ALCOA, who insturcted us in detail how to re-paint siding that had faded while under warranty. We did much of their warranty work. We were forbidden to us a brush or roller on aluminum siding re-finishing work. Spray only!
I equate it to taking your car to an auto body shop for repainting and the owner states that all the cars they refinish in their shop are re-painted using brushes and rollers, not spraying. How would you react to that statement?
There is just no comparison in the quality of a fine spray applied finish on metal when compared to even the best work with a brush and roller.
Most painters who brush and roll metal siding do so because they have not elevated and mastered their airless spray painting techniques, equipment and masking to a higher level, or they fear spraying for some reason.
If you run your hand over the finish and look closely, you can clearly see and appreciate the difference in quality between a roller applied finish and a spray applied finish. Granted, from the road they look about the same. The real advantage of a fine sprayed finish on metal shows up in years to come. The finer, smoother, tighter sprayed finish sheds water and atmospheric dirt and soot while the roller applied finish will tend to retain this fine gray soot in the texture of the finish. This leads to an uneven grayish cast in the paint that permantly discolors the finish.
There are those times when all the masking and spraying are just not justified or the risk of overspray is just too great, such as a case like this. In that case, we use 6" Wiz rollers (the gold foam series) with a thinner bodied acrylic, such as SW Super Paint, with a little EB added to loosen it up and help it level out as well as adhere to the aluminum siding. We work in the shade to slow down the drying time. The results are pretty good and the customer is usually very pleased, however, we can see and feel the difference between our roller application and the impeccably slick finish of fine spray application. We always opt for spraying any metal suface if possible, even metal entry doors, shutters, metal roofs, gutters and leaders and aluminum trim.