Varnishing wooden window frames can be a simple way to give your windows a fresh sheen, whether the wood is natural and untreated, or pre-stained. However straightforward the process, follow precautions and recommendations about weather, general preparation and methods of application. They are central to enjoying a beautiful finished product.
Plan Around the Weather
Make sure you do your project on a day with good weather, since your windows will be open while drying. Temperatures should be between 18.3 and 21.1 degrees C, and humidity should be regular to low. Choose a day with little to no wind, so that dust does not get caught on your wet surfaces.
Choose Windows Wisely
Your windows should be natural wood or pre-stained. If your windows are painted, stripping or sanding the surface of window frames down to the natural wood will compromise the integrity of the shape. The wood was likely painted in the first place because it was not high enough quality to leave exposed.
Even new brushes need to be cleaned. Prepare three different buckets of white spirit and clean your brush for about 15 minutes by changing buckets each time the spirits become cloudy. Pre-treat the window frames with white spirit, too. After the wood has dried, use an air compressor to remove any last bits of debris that may be hanging onto the surface from sanding.
Prepare Now, Do Less Later
Sanding and priming are two necessary steps in the varnishing process. Sand the wood with the proper grain paper, as determined by the softness of the wood. Once you're ready to prime, apply two coats of primer. Sand the wood with 100 grain paper after the first coat, and apply a second coat of primer that has been diluted by 30 per cent with thinner. After the second coat of primer, use 320 grain paper for the remainder of the project.
Don't Underestimate Gravity
If you are varnishing your windows while they hang in the wall (versus laying the frames atop a workman's bench), be especially careful to apply thin coats so they can dry evenly, with no drips. Do not thin your varnish in an attempt to make it lighter. This is a common varnishing faux pas.
Don't "Fix" It
Resist the temptation to "fix" your mistakes. Any varnished surface will inevitably attract some loose particle of dust or an accidental nick of the fingernail. Trying to remove a caught particle as you work will likely make it more noticeable. Its visibility will decrease after subsequent coats and sanding.
Go Against the Grain
For all coats of varnish except for the last, apply the varnish against the grain of the wood. This will allow the varnish to penetrate the grain the more thoroughly, while sanding in between coats will promote smoothness. Apply the last coat in the direction of the grain.