Ways to Seal an Exterior Wood Door

Surface Preparation

• A previously unfinished door must be sanded to remove any raised or rough areas. Initial sanding in the direction of the grain with 80-grit sandpaper should be followed with a final sanding using 100- to 120-grit sandpaper. This process not only will provide a smooth surface but also open the wood grain to better accept primer or stain. Vacuuming the sanded surface both with and against the grain will remove larger dust particles, and a final wipe with a tack cloth will complete the preparation process.

Marine Varnish

• Marine or spar varnishes contain a stain or colorant combined with a wood preservative that offers water and UV resistance protection. This product was developed to withstand the elements that a wooden boat might encounter and is therefore a more than adequate protectant for your exterior wood door. All six sides of a previously unfinished door should be covered with the product. End grain and bottom edge sections must be thoroughly coated for optimum results.

Primer and Paint

• For an exterior door, an oil/alkyd primer is preferred because it may then be covered with either an oil-based exterior paint or an exterior latex. A latex primer will only accept a latex topcoat. Some woods, such as cedar and redwood, contain a high percentage of tannins -- natural stains that tend to bleed through regular latex primers. An acrylic sealing primer with stain-blocking capability should be used if bleed-through is to be prevented with latex paint applications.

Maintenance

• For exterior doors that are south-facing and therefore subjected to long hours of exposure to the damaging UV rays of the sun, a reapplication of marine varnish should be performed every two to three years. Peeling, bubbling and fading paint or stain will signal the need for sanding and a new coat of paint or sealant. Your local paint or home improvement store is a good place to seek advice on new paint products and how they may be used in your particular application.