An orderly process is crucial in home remodeling. When you get the process right, things work smoothly. Your work remains clean and undamaged. When you get the process wrong, your current work messes up your previous work. This is the reasoning behind the question of whether to first refinish your floors or paint interior walls. It's a close call and both sides have merit. Much of it depends on shifting factors, too, some of which may be particular to your own project.
Refinishing Floors Before Painting Walls
If you simply have no floor coverings yet, just a subfloor, then you will greatly benefit by painting the walls and ceiling first. You can paint with pure freedom, even using a paint sprayer, and you can spill wherever you want. In this case, the decision is practically made for you already.
Consider the matter of appearance. Which surface's appearance is more permanent: floor or walls? Wall color can be changed over the course of a weekend. By Monday, your formerly pink walls will be blue. But it's more difficult to re-stain a floor to change its color.
In addition, the lack of baseboards and other floor trim means you can paint all the way down without any masking. In new-construction homes where no flooring has been laid yet, this is the way it works: walls are put up first, then the floor covering comes later.
When you run a floor sander around a room, there is the possibility of scuffing up your newly painted walls. Even though you will have removed the baseboards, enough activity happens that you might scrape, gouge, or scuff your perfectly painted walls.
Paint drips are a major concern. If you drip on a fully finished, sealed floor, as long as you get to the drip within a few seconds, it's almost like the drip never happened. If the latex paint dries, pry off the drop with a fingernail. Even so, pigment can stain the finished floor's surface.
Finally there is dust. Sanding floors creates a huge amount of dust. This dust settles not only on horizontal surfaces but clings to vertical surfaces such as walls. Flatter sheen paints seem to have the unique ability to attract dust. Even worse, the flatter the paint sheen, the more difficult it is to clean. Truly flat paint (paint at the extreme end of the sheen scale) can be so difficult to clean of dust that it is almost easier to entirely paint the walls again.
Painting Walls Before Refinishing Floors
One reason why homeowners may want to paint the walls first is that they fear dripping or smearing paint on their newly finished floor. Floors are expensive, but walls are not. It can be difficult to clean paint off of a floor. Walls are not fun to patch up, but they are still easier to fix than flooring.
If you paint walls first, some homeowners may think that it is possible to paint with relative abandon, then sand out your paint drips. Paint that has dripped and hardened on a sealed surface will come off floor sanding. But it only makes your job more difficult, plus it gums up the sandpaper. If the floor happens to be raw wood, paint can seep into the wood and stain it almost beyond repair. You would have to sand deeply into that raw wood to remove the paint pigment. So, even if you choose to paint the walls first, it's best to protect your flooring from paint drips.
Making the Choice
The final decision, of course, depends on your own situation, as well as your own likes and dislikes.
Floor finishing is semi-permanent. Stained flooring retains its color for a long time, and it's difficult to sand it all out. The floor will have a certain look, whether glossy or semi-glossy, or a certain hue, and the look of the walls should follow from there.
Paint drips are a valid concern, whether you have previously finished the floor or not. The best way to make sure that your flooring stays clean is to not get paint on it in the first place. Be sure to purchase a canvas dropcloth. A good dropcloth is a great investment in your house because you can use it repeatedly. Plastic dropcloths must be thrown away, plus they are slippery.