If you wish to varnish a wood door, there are certain steps you can take to make sure that the varnish lasts a long, long time, without checking and peeling.
The first consideration is whether the door is new, or one that has already been varnished.
Here are the steps to varnish a wood door that has never been varnished before.
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Not Varnished Or Coated Before
Determine if the door is new wood and has not been hung and exposed to the elements or allowed to weather in any way.
Even though this is a website about interior painting tips, a front door can be both interior and exterior, with one side exposed only to household ambient temperatures and light, and the other side to possible weather and bright sun, in other words, outside elements.
Also, ensure that the wood in the door hasn’t a “mill finish”.
To check for both, spritz or sprinkle a little water over the entire surface to be varnished. Watch to see if any of the water beads up.
If the water beads anywhere, that surface needs to be sanded to break the surface seal and to allow a drop of water to quickly penetrate into the wood.
If water can’t penetrate, it’s not likely that any varnish can either, so surface sealing must be removed or you will not get a finish that will last.
Door Exposed To Elements
If you intend to varnish a wood door that is exposed to the elements, the need for multiple coats of varnish is critical.
Even if the door is not exposed to other than the sun, through a clear glass or screen storm door, for example, that is an exposed door in my lexicon (heat and UV) and multiple coats are needed.
Whether you use an alkyd based or varnish, or you use one of the acrylic-based varnishes (waterborne), if you want a finish with long life, you must thin the first coat of varnish.
If it is an alkyd or polyurethane, you will not thin it with water. Follow the instructions on the can to determine the ideal thinner.
If it is an acrylic varnish, thin with water (always check the directions anyway, to be sure).
You Must Thin First Coat
Thin the first coat by 20%. That’s one cup of thinner to 4 cups of varnish.
Thinning the varnish will allow it to penetrate the wood fibres farther, creating a nice, clean, well-anchored base coat for the rest of the topcoats to bite into.
It may be necessary to lightly sand the first coat if fibres rise. For that matter, the pros will often lightly sand between every coat, to ensure that the last coat of varnish is as smooth as possible. A very light grit, about #150 or so, is recommended for this light sanding.
Shaken Or Stirred
You must either shake or stir varnish before you apply it.
If you shake, yes, there will be bubbles in the varnish that may take overnight to dissipate. Bear that in mind if you have the paint store doing it for you.
It’s not a bad idea to have them “spin” it if you aren’t using it the same day, despite what they may tell you.
If you don’t stir or shake varnish, the result may be an uneven sheen on the varnished wooden door when it cures.
Apply the varnish with a brush, roller or spray. Allows the first, thinned coat, plenty of time to dry before applying additional coats.
Now, the thing about varnish is, if you don’t put on four, or five coats of varnish, then your surface will degrade very quickly.
Even with these multi-coats, the nature of varnish is that it must be renewed with a fresh coat every year or two. You need to upgrade the coat of varnish before it starts to discolor or crack.
If you wait that long before adding another coat, you will need to strip back to bare wood and start again.
The more coats you apply when you varnish a wood door, the greater the “build” and the greater the weather and exposure resistance.
Also, bear in mind that varnish adds thickness to your door, and if the door is a tight fit when you start, four or five coats of varnish may make it stick.
This line will shortly be a link to a page about varnishing an already varnished door. Please bear with me while I write that page.