Noob Lord paints an interior door

What do you need to do the job

1. Oil based enamel paint (Gloss or Semi Gloss. Matt enamel doesn't exist.)
2. Water based undercoat paint.
3. Brushes. (Finishing brush)
4. Turpentine for cleaning up the oil based enamel.
5. Saw horse to rest the door on.
6. Sandpaper (80 up to 240ish grit)
7. Sander.
8. Tweezers.
9. Roller with vinyl sleeve.

What paint to use:

You should use enamel paint for the final coat because it's harder wearing than the other paints and more scrub-able than other paints.
You can get water based enamel. Then you can clean up with water, but the trade brands don't do it so it will cost more if you get water based enamel, although you will save on buying turps and extra brushes. I've read online that oil based enamel is harder wearing than water based enamel.
Personally I'd buy Walpamur or Taubmans Tradex oil based enamel because it's about half the cost of the other brands. I'd buy in 4L because you'll end up needing it and they only sell it in 4L.
You will want to also buy a water based undercoat paint.
I have tried Dulux Aqua-enamel and it was no better than Oil based on getting a nice finish. But I've not tried "Taubmans Ultra Enamel". Both of them are almost double the price of the trade paint. 

What to do:

1. Thoroughly sand the door with 80 grit to get a flat surface. (Assuming the door isn't in great shape when you start.)
2. Apply undercoat, let dry and sand with 200 grit. Then repeat till you have a really smooth surface.
3. Roll on enamel paint, then finish with a "finishing" brush. The finishing brush is more to wipe off pain than apply paint and it's to remove the stipple marks left by the roller.

Things I've learnt:

1. You need a lot of time. It takes 12 hours or more for enamel to dry and so it will take days to finish the job
2. It's very important you start with a good surface to the door. So sand it thoroughly before you start with 80 to 120 grit wet sand paper.
3. Always use wet sand paper. Because a. otherwise the dust goes everywhere including your lungs. b. dry sandpaper clogs, even the 'no-clog' sand paper clogs. c. then the paint clogs rip the paint.
4. Dilute the paint to make it flow better. Turps or water depending.
5. You need to do this job inside where you can stop dust blowing on to the paint while it dries.
6. If it's cold and wet it takes longer to dry.
7. Then paint with undercoat, and when paint is dry then sand till you get a nice surface. You want to do this with undercoat because it's cheaper paint, and dries faster and can clean up with water. (I am assuming you have a door without a great surface to start with.)
8. You can use a roller which is great in that it shows no brush marks. But it creates a stipple pattern. (Both the vinyl and micro-fiber sleeves leave a stipple pattern.) The stipple pattern looks OK to me but if you have to scrub the door then where you scrub you can scrub the stipple pattern flat. This then sticks out like a sore thumb. So if you are going to use a roller you should finish with a finishing brush. You should mainly only be using rollers.
9. Use a nice wide 750mm brush and you are going to use the very tip to 'tip off'.
10. Then paint with the enamel and do at least 2 coats of enamel.
11. You can use a roller then a 'finishing brush'. The finishing brush is designed to take paint off. It's a very wide brush and you brush the rolled door to give the door a brush finish. It gives the speed of a roller, with a brush finish.
12. Too much paint and it will drip off your brush leaving blobs so going crazy with the paint doesn't work great. You can also have a problem where the paint on top hardens and the paint underneath is still soft. Then if you push with your finger it leaves a finger print, if you try and sand the paint on top will sand through then you are sanding wet paint. Yuck.
13. Dulux paint is double the price of trade and not worth it. But you might want o use a paint additive and also dilute.
14. The door you are painting is probably very uneven and this will cause all sorts of problems if you think you can sand it flat. Don't try it doesn't work. You can't. And you can't get a flat finish on an uneven door. You can still get a very nice finish though, just don't try and sand it flat.
15. Keep the paint tub sealed. Bits get in otherwise. Just take out what you need from the tin, otherwise you'll get bits in the tin if you put pain back in.
16. I used a draft excluder to 'tip off' and allowed me to do a perfect 1 direction tip off.

Tips I read online:

1. Sand with 240 grit paper.

2. Only use gloss.

3. add penetrol to anything oil based 

4. use a foam roller, top to bottom then tip off, if you have insufficient paint or too thick paint you get drag marks.

5. bang nails in to the bottom and top of the door so you can pain one side, flip and the door rests on the nails and you can paint the other side. But you'll need someone to help and a way to make sure the door doesn't slip. I didn't do this.

This is the best article I've seen with a load of tips.
https://www.familyhandyman.com/painting/techniques/painting-doors/