You can stain the existing wood on your stairs, as long as you adequately prepare it prior to application. If the existing wood is bare, staining should be relatively fast and easy; if it is varnished, tedious prep work is required. Learn the proper strategies to promote an attractive, uniform finish, or disappointing to catastrophic results are likely.
If your stairs are composed of bare, unfinished wood, no sanding is required; simply dust the wood prior to application. Wash exterior stairs using a hose or pressure washer. If your stairs are coated with varnish or wood sealer, extensive sanding is necessary. Varnish and other types of wood sealer prevent stain absorption. You must eliminate this finish, or the stain will puddle and drip. Sand the stairs until they appear dull.
Once the stairs are free from varnish and wood sealer, they'll accept a stained finish. Unfortunately, different types of wood accept stain better than others. If your stairs are made of softwood, such as cedar or pine, any stain will suffice. If they are composed of hardwood, such as walnut or oak, they require a slow-absorbing gel stain that will promote a uniform finish.
The right tools will not only make staining easier -- they will prevent unnecessary drips and splatters. Choose a broad, 3-to-4-inch china-bristled paintbrush to stain your steps. A 2-inch china brush and/or mini-roller will provide the best results when staining thin rails and balusters.
Proper sanding methods are critical; don't sand against the wood grain, or catastrophic damage to the wood may occur. In addition, while liquid stains work well with softwood stairs, they tend to dry unevenly on stairs made from hardwood. If you are unsure what type of wood your stairs are made of, choose a thick, slow-absorbing gel stain to be safe. Gel stains work well with both soft and hard woods.