The cost to paint an average size room (10X12) ranges from $380-$790, not including ceilings, trim or cost of the paint. DIY, this can cost between $200-$300. When estimating the cost, painters will start with how much paint will be required to complete the job. To know this, they first need to know the size of the area to be covered. The easiest way to calculate the size of the paintable area is to add together the length of the wall and multiply it by the width of the room from floor to ceiling. The resulting amount is the room's square footage. This total is a starting point, as it is not all paintable surface. The painters won't paint the windows and doors, for example, and they must account for ceiling trim and baseboards as well. The next step is to subtract the area of the doors and windows -- along with the square footage of the trim and baseboards -- to get an average. Then, use the same calculation (length x width) on the windows, doors, trim and baseboards, and subtract all of those numbers. The result of this equation is the square footage of the room's walls. This is your surface area number. (Painters will typically add a little square footage back in to this amount to account for extra paint, which may be required.)
Freshly painted walls often look blotchy. The color is uniform, but the sheen isn’t consistent. This usually occurs over the holes and cracks you patched with a filler or drywall compound. The porous fillers absorb the paint, dulling the surface (a problem called “flashing”). When light hits these dull spots, they stick out like a sore thumb. The smooth patch also stands out in contrast to the slightly bumpy texture of the rest of the wall. A quick coat of primer is all it takes to eliminate flashing and texture differences.
Most pros don't bother cleaning brushes and rollers if they are going to use them the next day on the same job. "Latex paint dries slowly in cold temperatures," says Maceyunas. For two-day jobs, he wraps the rollers and brushes in plastic grocery bags and sticks them in the refrigerator. "Just allow the roller to return to room temperature before reusing it," he says. Roller covers are almost impossible to clean thoroughly. Most pros buy new covers for each job.

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