Varnish is a clear protective final material used in woodworking. It is a mixture of a drying oil, resin and thinner. Most varnishes are glossy, but a varnish designed to produce semi-gloss, or satiny sheens use flatting agents. Varnish has little or no color. Apply over wood stains as the final steps to achieving glossy protection.
Varnishes harden directly as soon as the solvent has evaporated, or the varnish hardens after evaporation of the solvent through curing processes. Water based and acrylic varnishes dry when the water ingredient evaporates. Polyurethane varnishes, oil, and epoxy lacquers stay liquid after water evaporation. They do begin to cure by undergoing stages from liquid to syrupy, to tacky or sticky to “dry to the touch” and then to protective hard.
Always ensure that you are using the best polyurethane wood varnish that you can find. A high quality finish requires a high quality wood varnish so do not scrimp onf the quality.
How to Varnish Wood
Check the weather on the day you are planning to varnish wood. Heat and humidity slow down the drying process which gives time for dust and particles to settle on the wood.
The indoor temperature when you are varnishing should be between 70 and 85°F or 21.11 and 29.44°C. If the temperature is over 85°F the varnish will dry too quickly, and bubbles will form on the surface of the wood. Remove the old varnish. Apply a paint stripping solution and follow the manufacturer’s directions. Sand the wood to remove any gloss. Varnish will not adhere to old gloss or chips and defects.
Use a damp cloth to remove remaining dirt and debris and allow the wood to completely dry. Clean up your work area to prevent dust and dirt from adhering to your varnish.
Mix wood varnish with pure turpentine. Turpentine thins the varnish and helps to seal the wood. Apply a very thin mixture as the first coat. Use a foam brush and allow the first layer to dry overnight.With 280-grit sandpaper, sand the first coat. Wipe with a dry cloth to remove loose dust and particles.Next, apply the first regular coat of varnish with a foam brush. Brush varnish with or against the grain.
Allow the coat to dry. Gently buff with 320-grit sandpaper and lightly brush off the dust.Apply as many subsequent coats of varnish as you think is necessary. Do lightly sand between applications. On your last varnish, go with the grain and avoid sanding after the final coat. If you live in a humid area, look for varnishes that dry in humid conditions.Use washing soda to water when pre-treating the wood. Pretreating will help remove more dirt and debris.
Take the proper safety precautions when using any type of powerful paint strippers or wood varnishes. Stay away from heaters or any type of fire. Varnish is extremely flammable.
Do not use cold varnish. The varnish must be room temperature or warmer to flow easily. Place the varnish can in a bucket of hot water if you need to keep it liquid
Do not use steel wood to scuff the wood between varnish applications. Steel wood fibers can embed into the finish.