Varnished wood looks appealing, warm and welcoming. Varnishing wood is a straightforward process and, as with all DIY projects, the secret to achieving a durable, professional-looking finish is in the preparation. You may wish to allow the natural colour of the wood to show, in which case choose a clear varnish. If you'd like a deeper colour, select a coloured finish, such as oak or mahogany. Hardware stores usually have samples on display.
Select a varnish suitable for your needs. In most cases, a water-based varnish will be fine. Use an oil-based polyurethane varnish for items that need a hard-wearing finish, such as outdoor furniture. If you prefer a shiny finish, choose gloss, otherwise select satin or matt. Water-based varnish is thinned with water; oil-based with white spirit.
Spread newspapers on the floor where you will be working on the item (unless you are varnishing the floor). Provide good ventilation. Assess the condition of the item. If it has old paint or is damaged, remove the finish and make any necessary repairs. Remove old nails and fill holes with appropriate wood filler.
Don a face mask and gloves. Sand the item thoroughly, starting with coarse sandpaper and progressing to a fine grade. If varnishing a floor, consider using an electric sander. Remove dust with rags and white spirit between sandings. Ensure all dust is removed before varnishing. Lingering particles will spoil the finish.
Mix 3 parts varnish with 1 part thinner in a container. The first application is the sealing coat. Apply the thinned varnish to the item or floor, using long strokes and following the grain to avoid runs. Clean brushes thoroughly.
Allow to dry thoroughly. Water-based varnishes dry within hours, but oil-based varnishes may have to be left overnight.
Sand lightly with fine-grade sandpaper. Wipe with clean rags dampened with thinner to remove dust. Apply second coat of varnish, undiluted. Allow to dry. This will be sufficient for some items; however, apply another coat or two for heavily used articles. Sand between coats with fine sandpaper and remove dust before applying varnish. Let the item stand for 72 hours before touching or using it. Varnish will harden off over a period of days.
Don't shake the tin of varnish or stir vigorously. Doing so will cause air bubbles to form, which will spoil the finish. Follow the manufacturer's instructions for application, drying times and brush cleaning. Dispose of varnish and used solvents according to local waste-management guidelines.