Bamboo isn't as porous as wood, but penetrating oils still soak in, and if you have a newish piece of bamboo furniture, it may have a coat of tung or linseed oil. That's not an obstacle to painting the piece, but you want to clean it thoroughly first, because penetrating oils tend to pick up dirt. Even though you may lose a little in overspray, applying paint by spraying is a sure-fire way to get even coverage in all the nooks and crannies.
Preparing the Bamboo
The quality of every painting project is a function of how much effort you put into preparation, and in the case of unfinished bamboo, you'll expend most of that effort in cleaning. Scraping and sanding are necessary only if the piece has a film finish of varnish or paint. If you have to remove an old finish, consider power washing as an option.
Scrape and scrub off any peeling or flaking paint or varnish, using a putty knife and a wire brush. A rotary tool fitted with a detail brush provides an effective tool for getting material out of hard-to-reach joints quickly and with minimal collateral damage.
Mix a solution consisting of 1/2 cup of trisodium phosphate per gallon of water. TSP is a strong detergent that removes surface dirt and grime as well as residual oil that interferes with paint adhesion. It will also strip some of the paint and varnish -- if there is any.
Put on goggles and rubber gloves and wash the piece thoroughly with a the TSP solution, using a sponge. Rinse well with clear water when you're done, then let the piece dry.
Priming and Painting
Bamboo furniture frequently incorporates rattan -- which is a woven grass -- and wicker, which can be virtually any material, including paper, grass or leaves; the word "wicker" refers to a technique rather than a material. You can paint both rattan and wicker in the same way that you paint bamboo, but both give you another good another reason to spray the paint rather than brush it. If you prefer brushing, however, there's nothing preventing you from doing that.
Bring the piece outside, and set it up in a sheltered area where it won't be affected by wind or humidity. A garage or covered work space is ideal. Put newspaper on the ground and set the piece upside-down on the paper.
Spray the underside, including the legs, with oil-based wood primer, using an aerosol can or an air gun with a compressor. An oil-based primer -- preferably one that contains shellac -- has better adhesion and stain blocking ability than latex primers and will ensure an even topcoat that stays put.
Let the primer dry, which shouldn't take more than an hour, then turn the piece right-side-up and spray all the rest of it. Let the primer dry overnight.
Invert the piece again and spray the underside with an oil- or water-based enamel. Latex enamel is easier to clean up, and you won't have to worry about breathing fumes, but you'll get longer wear from an oil-based product. Let the paint dry -- which might take anywhere from two to eight hours, depending on the type of paint you use.
Turn the piece right-side-up once more and spray the any part of it that isn't already painted. Let the paint dry, then spray a second coat, if necessary.