Painting doors can be a little difficult, especially if you choose to paint them while they are installed. For the best result the door should be removed, stripped of all hardware, and placed in a horizontal position on two sawhorses before painting. This will provide a much better working position for applying the paint and a much better outcome.

A flat panel door can be painted with a roller then stroked over with a brush. If the paint from the roller is drying too quickly before it can be brushed over, use a paint additive to slow the drying time. Using this method when there are several doors to paint will save a lot of time.

Rather than using a roller us only a brush a good method if you paint small sections at a time by moving across the door and then down. Try to paint quickly to maintain a "wet edge". The finish will be smoother and lap marks can be avoided. Lap marks occur when the starting and stopping edges of strokes begin to dry during painting and fail to blend in with the wet paint.

How to paint a flat panel door:

For best results remove the door from the door frame, lay it on two sawhorses and remove all the door hardware. Painting a door while it is installed in the vertical position is almost certainly not going to come out looking like a professional paint job.
Check the door casing to insure that it is in good condition. If there is old dry paint on the casing it should be sanded before painting.
Check the door for dry paint and sand as necessary before painting. If the door is made of metal, use automotive primer paint on any shinny areas of the metal before applying the finish paint.
Prevent lap marks caused by painting over partially dried paint by painting quickly before it has a chance to start to dry.
Let the first side dry and turn the door over on the saw horses and paint the opposite side.
Finally, paint all the door edges.
Let the door dry thoroughly and install the hardware.

That is how to paint a flat panel door and have a professional looking finished paint job.

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