If sanding is your least-favorite step, then it's certainly possible to paint furniture without sanding. But to do so with favorite results, you should clean the wood's surface AND use a high-quality primer and/or paint. You can also use liquid paint remover to scrape off the old paint.
If the wood's previously been used and painted, again sand it down, initially with a light-grade grit, bearing in mind that the purpose of sanding is to provide a solid base for the new paint so it's not necessary to remove all previous paint but the finish must be clean and with no loose or flaking areas.
Luckily, you don't need to remove all the finish from the surface. Just roughing up the surface with fine grit sandpaper is enough to get the paint to stick to polyurethane. With a little elbow grease, you'll be ready to paint in no time!
Start by lightly sanding the entire surface with 100-150 grit sandpaper. You don't need to spend a lot of time on this, just quickly sand the piece. This will help roughen the surface just a bit so the primer and paint have something to stick to. Next, apply a coat of a good primer.
You probably don't need a primer. If the current wall is smooth, clean and covered with the same type of paint (both are oil-based for example), you can head straight for the paint. You need to fill holes, spackle and sand*, maybe even cut a new piece of drywall in to the existing wall.
You may need an undercoat for wood, but there is no need to apply any primer, as the surface is already painted. If it is not practical to sand down to remove the sheen, an “adhesion” primer like Zinsser B-I-N will help your paint bond to the surface. It has the additional benefit of blocking stains and odours.
But before you can repaint the deck or stain your fence, you need to learn how to remove paint from wood: In most cases, it's not the best idea to simply paint over an old coat of paint, particularly if it's peeling or chipping.
Begin surface prep for painting by removing any loose, peeling paint with a paint scraper and sandpaper. Sand all edges to smooth the surface and help the new paint adhere. Scrub all surfaces with a mild detergent and a sponge or rag to remove all dirt, grease, oil, etc. Rinse surface well and allow to dry.
Sanding a surface removes the top glossy layer, allowing the substance to receive the primer. Without sanding the surface in advance, the new coat of paint won't stick to the previous layer. In addition to stripping the outer layer of gloss, you can also use sandpaper to correct imperfections and remove stains.
You cannot paint directly over the top of peeling or blistered paint. Instead, you'll need to remove flaking paint with a palette knife or similar tool. Then, sand down the area to achieve a smooth finish. Apply a suitable primer before you paint.
Some people will say as long as the paint is fully cured you should be okay. However, if you know you are painting over oil-based paint then I would use a primer so that you don't end up with chipping and peeling paint.
If the existing paint is in good condition, with small spots, stains, and damage, and there is not much difference between the type and color of the new and old paint, you can repaint the walls without removing the whole paint.
As a general rule, it is possible to paint over already painted wood without sanding it first if the surface is not damaged or the previous paint job is not peeling or chipping off. Simply prepare the surface by applying a high adhesion primer. Once the primer has fully dried apply the paint.
With fresh drywall, the substrate actually absorbs a coating really well, like a sponge. However, because it absorbs so well, without a primer coat, you'll experience uneven coverage, especially along drywall seams. This means you'll need to apply more paint to finally get an even coat.
When painting over oil based paint it's very important to sand the surfaces and prime with an oil based or shellac primer. These types of specialty primers are what will assure a good bond. Quality paint primers are designed to stabilize the surface, harden and bond the surface.
Painting over dirty walls, excess moisture, improper prep, and using latex paint on top of oil paint can all affect the paint's adhesion and cause it to eventually begin flaking off. To solve the problem, you'll need to remove the peeling areas and start over with fresh coats of primer and paint.
Chemical paint removers deliver the best results, remove varnishes and paints faster than sanding, and tend to be the least harsh. Care needs to be taken when using chemical strippers, however, as these present their own care and safety issues.
Often used as a nail polish remover, hydrogen peroxide is also equally adept at removing paint. We recommend using gloves and keeping the room well vented if you are indoors. Using hydrogen peroxide is simple. Dap a cloth, scrubber or steel wool with hydrogen peroxide and cover the surface with the liquid.
Natural Options to Remove Paint From Wood
It's easy to heat a vinegar water solution and dab the warm liquid on the surface. Let it sit for 15 minutes before scraping. Retry if it doesn't work the first time. A heat gun is another excellent option, also softening the paint.
The problem could be with the paint you are using. It could be defective, old, or a low quality paint that doesn't cover well. Another option is to try priming an inconspicuous spot, let it dry, then paint over it to see if that helps. If so, go back and prime all the walls with a stain blocking primer.
Painting over flaky patches or paint chips can be easily rectified, larger areas must have all the peeling paint removed before attempting to repaint. This can prove problematic as some of the paint will refuse to scrape off and the use of a Heat Gun must be used to soften the stubborn paint to allow for removal.