Paint roller covers have three basic considerations, the nap and core material, length of the cover, and the length of the nap. All three qualities are important and the choice is determined by the square area of the project, the surface, and the chosen type of finish paint. A good painter must have knowledge of the proper painting tools for the job as well as knowing how to paint.
Roller Cover Nap and Core Material
Dispensing with the least complex consideration first, inexpensive roller cover cores are made of cardboard, which will breakdown in latex and oil paints, or poor quality plastic, which might soften in some solvent-based finishes. They might also shed fabric like mangy dogs. Do not buy inexpensive roller covers.
Roller cover naps come in a variety of materials. Common examples are synthetic blends, polyester knits, lambswool, mohair, and foam, and a range of specialty covers, such as nylon looped for applying textured paints. The nap material is an indicator, to a degree, of its use. The blends and knits are good general-purpose covers for painting ceilings and walls, with oil or latex. Lambswool is a good material for doing large areas with low sheen paints, and some solvent based, as it holds more paint than synthetic covers.
Mohair, foam, and shorter nap synthetics are the choice for applying oil based and higher sheen latex paints, such as semi-gloss and up, as well as clear coat applications. These nap materials are especially useful for painting trim surfaces, such as doors, shelving, kitchen cabinets, etc. Mohair is also a good choice for rolling oil paint on smooth wall surfaces. This class of covers applies a lower mil, thickness, of paint and leaves a closer to factory finish appearance than their synthetic cousins.
Proper Nap Length of Roller Covers
Nap length, similar to nap material, is a general indicator of its use. While mohair is a fixed length nap, the synthetic covers vary in nap length from 1/4" to 1 ¾". Foams come in different thicknesses, which determine the amount of paint held. Smoother surfaces require less paint to cover while rougher surfaces require more. The less viscous paints, such as oils and clears, require less nap, while thicker paints, such as flat, require more nap. That is a good general understanding of how nap length relates to paint coverage.
A nap length of ½" would create a mess painting doors with any type of material, though ideal for rolling ceilings and walls, even with oil for the experienced. A length of 3/16" would be ideal for doors, though difficult for anything more than rolling oil or high sheen latex on smooth, perfect plaster walls. On rough surfaces like stucco and textured walls, regardless of the material in use, long nap covers, ½" or more, are required to get coverage, with rough stucco requiring up to 1 ¾".
Choosing the Right Roller Cover Length
Obviously, the proper length corresponds to the square area of the paint project at hand, and applies more to quantity rather than quality. Cover lengths range from 3" to 18", roughly. Moreover, each length generally comes in the range of nap lengths. An 18"x1/2" cover will cover twice the area than a 9"x1/2" in the same time, which makes the larger more productive for floors and single ceilings that span multiple rooms. A combination of cover lengths is sometimes useful on the same project.
In painting powder rooms, kitchens, and some trim projects, a 7" length will prove less bulky and more manageable, while a 4" cover works nicely for finishing kitchen cabinets. Remember, that is a 4"x3/16" or mohair cover. Shorter length covers also serve nicely for applying paint prior to laying off with a brush. Be careful not to get too far ahead, as some paints begin tacking quickly. It is also possible to shorten a long cover, carefully, with a hacksaw, carefully.
Understanding Roller Covers
While not complex, there are certainly considerations for the DIY painter in choosing the right roller cover for an interior painting project. The range of options is large, but what may be available might be regional or limited to what the local paint store might carry. The goal of this discussion, combind with an earlier discussion on paint rolling technique, is to provide a general understanding and give the DIY enough education to sound knowledgeable when discussing needs with the paint store rep.
