Bamboo has a natural silica layer that protects it from moisture damage. Unfortunately, this layer may disintegrate due to wear and processing. A solvent or polyurethane sealant can protect bamboo for years; however, when amateurs attempt to apply sealants to bamboo, flaking tends to result. Before you apply any type of sealant to bamboo, strip down the remaining silica, or adhesion problems will prove inevitable. Choose the right type of sealant based on whether the bamboo is bare or stained.
Equip a power sander with 60-grit sandpaper. Remove the natural outer silica coating, using the power sander. Sand in the direction of the wood grain until the bamboo appears dull.
Exchange the 60-grit sandpaper with 100-grit. Sand the bamboo until it feels smooth.
Wipe the bamboo surface with tack cloths; this is critical as sawdust will interfere with the application process.
Add a stained finish now if you want to. Apply gel stain to the bamboo, using a china brush; wipe the wet gel from the surface, using rags. Let the stained finish dry for three hours. Wash the brush, using fresh white spirit. Skip this step if you do not desire a stained finish
Apply a solvent-based wood sealer to the bamboo, using the china brush. Wood sealers tend to sag on vertical bamboo surfaces. If you notice this, smooth the sagging areas with the brush. Let the sealer dry for two hours. Apply another coat.
Use varnish on bamboo wood furniture.
You may also use a polyurethane wood sealer on bamboo. However, you cannot apply polyurethane over bamboo finished with oil-based stain.