Kitchen cabinets are one of the most abused surfaces in your home. Your cupboards face daily assault from greasy hands, steamy pots, sticky jelly jars and many other indignities. A quality paint job protects and beautifies a cabinet's wood -- or particleboard -- box and doors, but you can extend the life of your cabinets' finish by topping off the paint with a tough sealant coat. A sealant is particularly valuable if your cabinets boast a faux finish or other decorative coating. Water-based polyurethane varnishes provide enhanced water resistance, chemical resistance and scratch resistance without emitting fumes that might adversely affect the flavor of foods.

Step 1 Inspect for Lead

Check the old coating for the presence of lead using an EPA-recognized lead test kit if your cabinets were installed and painted before 1978. These kits are available at paint stores, hardware stores and home center outlets. If testing confirms the presence of lead, contact your community's health department or a certified lead abatement professional before disturbing the cabinet's existing finish.

Step 2 Prepare the Cabinet

Empty the cabinets completely. Remove the handles or knobs from the cabinet doors, using a screwdriver. Put the handles and the fasteners aside for re-attachment later, unless you're updating to newer handles or knobs.

Step 3 Mix Up a Degreasing Compound

Slip on a cotton face mask for dust protection, then mix 2 ounces of powdered trisodium phosphate into a gallon of warm tap water. Dilution rates may vary by manufacturer; read the package's instructions for specific guidelines. The TSP cleans and degreases the paint surface.

Step 4 Clean the Cabinets

Spread dropcloths over the countertops and flooring to protect surfaces from accidental drips or spills; be sure to cover surfaces completely. Wipe down all cabinet surfaces using a sponge impregnated with the TSP or TSP-substitute. Follow up by thoroughly rinsing off the TSP with a water-soaked sponge or cotton rag. Allow the cabinets to dry completely.

Step 5 Apply a Clear Primer/Sealer

Apply a thin coat of clear dewaxed shellac to all cabinet surfaces using a natural fiber paintbrush or a disposable foam applicator. Let the shellac dry for an hour; then gently sand away any surface irregularities using 220-grit sandpaper. Wipe off any sanding residue with a dry, lint-free cotton rag or a tack cloth. Apply a second coat of the dewaxed shellac; then sand and wipe clean after one hour as before.

Step 6 Brush on the Sealer Coat

Use a high-grade synthetic fiber brush to apply the smoothest possible polyurethane-finish coat. Start by applying a single thin coat, and let it dry for two hours before gently sanding and polishing away any bubbles in the coating. Thoroughly wipe off all sanding residue before applying a second thin coat. After allowing a couple hours for drying, sand any surface irregularities smooth before adding a third coat.

Step 7 Re-attach the Handles

Wait at least 24 hours for the finish to cure before attaching the handles or knobs and restocking your cabinets. Read the product label and technical data sheet to confirm the manufacturer's recommendations.