1. Sand your door first sand the flat areas of the doors but be careful not to add too much pressure, so you make the door surface even and flat.
2. Add paint conditional to your paint There are various conditionals for paints to make them stick well to the door surface. Conditioning is different from adding water to make your paint thinner. A good paint conditional is Floetrol; it is very efficient in stopping those brush marks from appearing.
3. If possible, paint your door while it is in a horizontal, flat position: if you are painting your door before it has been fixed or you have a door that can easily be unhinged from its frames, it is best to paint them while flat on the ground.
4. Apply Primer correctly Primer is the biggest cause of brush marks because it goes on thick and dries fast, meaning your paints have little time to even out before drying. A good idea is to swap for a slow drying primer.
5. Use roller paint brush for second layers After using a regular brush for the first painting, use roller brush the second time; this helps remove brush marks and brings your door’s color out looking like an expert artist has painted it.