A nice little weekend project is to paint a door.  Typically thru time doors will get marked up and perhaps even dinged up some.  It could be so banged up you might think it needs replacing but a new coat of paint will do wonders to refresh a door.   Surface preparation is always the first step.  With this door there were dozens of nicks and scraps on both the front and back surfaces of the door. 

 So the first thing I want to do is get rid of those.  Step one is to sand down the door.  I wasn't too concerned about sanding out the dings.  For one thing typically on the inside doors the door skin is real thin and you are not going to get very far by sanding until you sand thru the door skin.  When you do that you have a whole different problem.   So I sand down the door and then clean off or 'tack' the door by wiping off the dust with a damp cloth.

Then I take a 6 inch wide scraper and apply joint compound all over the surface of the door taking care to make sure all the dents and scraps are filled.  When you do this you don't want to have a lot on there, just spread it out smooth with the scraper and leave it at that.   Take a look at the first picture below.

Here in St. Petersburg it took about 45 minutes for it all to dry before I could start to sand it off.   When dry I use a hand held sanding device that holds 1/3 of normal sanding sheet.   You can see the sanding device in the next picture.  You can buy them at Home Depot and other places for about 6-7 dollars.  You really want to use this too.  Holding the sandpaper in your bare hand will not work.  The reason it will not work good is the joint compound is very soft compared to the hardness of the door itself.  When you sand by had the pressure on the sandpaper is greater where your fingers are holding the paper.   This means that you can sand out the joint compound from the dents and be back to square one pretty fast.   With a flat sanding device it applys an even sanding plain across the surface of the door which will leave the joint compound in the dents and scraps.   Using the sanding device will get you a smooth flat surface every time.  Look at all those vertical scraps in the door.  At this point, which is after sanding, when you run your hand across the door its as smooth as glass.

 You need to prime the door before painting.  Priming will put a consistent coat over the surface so the paint coat will look great without any dead spots or streaking.  After I rolled on a coat of primer the door surface is as smooth if not more so than brand new.  After I get both sides done I typically hang the door back up but leave the door knob off.  I hang the door up because that way you can paint both sides at once.  This is also a great time to put new hindges and a new door knob on.  Chances are if the door is worn and dinged up the hindges and door knob are in sad shape too.