My painter tells me that he doesn’t paint all three sides of a vertical trim piece, only the front face. Is this typical, and if so, why?
This is called "Facing Off" the trim. This is the most typical way to paint trim boards. It saves time and there for saves money, allowing the painter to bib your job more competitively.
If you want the edges of your trim painted, "Wrapping the Trim", ask your painter for the cost of this option. It is labor intensive and is typically held back as an option.
Painting the trim of a typical house.
Both of these ideas are usually applied on the same house with a standard paint job.
1) Fascia Boards – The large face and the lip of fascia boards are always painted the trim color.
2) Corner Boards – Usually faced only.
3) Window Trim – The face and the lip at the window frame. This is typical with vinyl or metal clad factory finished windows.
4) Door Trim – The same as with window trim.
Any trim board can be wrapped, the exception is the fascia boards which have the bottom lip painted as standard. The effect can be dramatic on the right house.
Painting all the sides will not help you at all. What you are looking for is nice clean lines and painting the sides of the trim will only accent the bad. Believe me no one does this anymore. They use to do this up until the sixties.
Wrapping Trim Has Its Downside
Actually facing the trim out is preferred in most cases and delivers a crisper and cleaner look. The edges of the boards where siding butts up to the vertical trim is used for caulking purposes and looks better if it is painted with the siding color. Caulk rounds out the spot where the siding joins the trim making it is very hard to create clean straight lines.
When wrapping your trim with paint you really don't gain anything aesthetically. In most cases you pay more for wrapping and from a distance doesn't look nearly as good.