How to Repair Sun Damage on Front Door


I'm a novice when it comes to home improvement DIY work, and I'm interested in repairing some sun damage I see on my front door. 

On multiple websites (including yours), it's recommended to sand the door down then apply marine varnish.

Can you give me more information on how to “sand and prep the door like usual”?

(1) Do I have to take the door down and off its hinges? I'm petite and I'm hoping I don't have to take the door down. I'm hoping I can just sand and varnish with the door upright.

(2) Can I hand sand the door, or do I need to go out and buy a sander? 

(3) Can I just sand the old varnish off or do I need to sand away the paint on the door too?

(4) I understand it's recommended to put at least two coats of varnish on the door and allow each coat to thoroughly dry before adding the next layer. Can this entire project be completed within a day? If I need to take my front door off the hinges ideally I would like to have it back on when night falls.

Thanks in advance for you help!

The Money Pit Answer

Refinishing a front door is a great project for a warm weekend, because that's the time you need to allow all coats to properly dry.   Time the project so the door is dry at the end of the day, can be reinstalled overnight, and taken off again the next morning to finish the job. 
You can certainly work on this door upright, but the job is far easier - and possibly more effective -  if you take it off its hinges and work on it horizontally, on saw horses.  Not only will this let you do a better job sanding (and will be easier on your back), you won't have to worry about the finish dripping.  Removing the door might not be as difficult as you fear.  Once you pull out the hingepins, it comes off easily.  All you'll need is a friend to help you lift it onto a saw horse.

You asked about sanding.  You can sand by hand, though it's certainly a lot easier to work with a vibrating sander.  If you do opt for hand sanding and your door features detail such as raised panels, I recommend 3M's sanding sponges.  They can help you sand those spots that are hard to effectively reach with stiff sandpaper. 

Regarding your question about varnish, it's hard to tell from your question what type of door you have. If it's a wood door you're staining, you may have to touch up  the stain after sanding it - especially if you sand it down to raw wood. The reason I recommend marine varnish is because it has a high degree of UV protection, which slows sun damage to door.  If it's painted, you don't need to varnish it, and can simply prime, and then paint it with exterior grade enamel paint.

In terms of how long you should let varnish or paint dry, simply follow the label instructions, and when it doubt, wait it out!  You never want to put a coat on prematurely, and if the previous coat is still tacky at all, hold off.

If all of this this feels like too much of an undertaking and you're ready to simply replace the door, fiberglass doors are the way to go, and can look almost like wood.