[This is part of my How to Install Moldings series.]
What is a Plinth Block?
For our purposes, think of it as the foundation of your door trim, pilaster or column.
Its strictest definition is rooted in the Classical Orders, and serves as a load-bearing unit, but our plinths are merely decorative.
However, when using plinth blocks in a molding pattern they must at least appear to serve their original function. Ignore this and you risk losing the visual point you are trying to make with them.
Plinth Blocks As Intersections
In the example below, I’ve made a model of the door trim and baseboard I want to install.
I’ll make the plinth block about 1/8″ thicker than the thickness of the baseboard. That way it acts as an intersection between the two dissimilar sized moldings.
In carpenter-speak, you would say the plinth block stands proud of the door trim and baseboard.
Why Not Make the Door Trim & Baseboard Flush With the Plinth?
In a perfect world your door jamb and drywall will both be flush and you could simply make your intersection moldings flush too.
However, that’s not the world we live in.
Door jambs are rarely flush with the drywall. And even when they are, this side might be perfect while the other side is totally out of whack.
So creating a plinth block that stands proud of the door trim and baseboard give you some wiggle room to account for misaligned jambs and walls.
Below I made this Craftsman plinth block wider than the flat-stock door trim so the reveal between the trim and plinth block created a step, a theme repeated in the baseboard.
Traditional or Neoclassical Plinth Blocks Before and After
Everyone loves home improvement before and after pictures. Here’s one involving plinth blocks.
Below This is the left side of the door trim in the above photo.
Below I installed this architrave molding around the opening that leads from this master bedroom into the hall separating the his and her closets, and the plinth block acts as the perfect intersection between the moldings.
Should the Plinth Block Be Taller Than the Baseboard?
Not always, no. Below is an example of a Victorian style plinth block I made that did not exceed the baseboard height.
Pre-Fab Plinth Blocks
The plinth blocks in the two pictures below are the most common style sold in most retail home improvement stores.
However, they are purely Victorian in style, and so should really only be used with the reeded casing you see below (also commonly available) or with a flat-stock pilaster.
Below This is another common Victorian style plinth block.
This plinth block allowed me to neatly terminate the three-piece Victorian baseboard below the smaller door trim.
Below Dissolving this large baseboard into the door trim and plinth block was difficult enough as it was, imagine how awkward it would have looked if I hadn’t used a plinth block.
Traditional Style Plinth Blocks
Many molding and millwork companies make plinth blocks that match the profiles of specific door trim molding they make. This is a really great way to go, but there are no rules that say they have to match perfectly.
In the photo at the very top of this post you can see the traditional style plinth blocks that I bought at a local lumber yard. I didn’t like their matching door trim that went with them, but they worked perfectly for my own design.
If you want to make your own traditional plinth blocks, you can see step by step how to make a simple design here: How to Make PLINTH BLOCK-100.
Or, if you want to build the simple square plinth blocks, you can see how I built them for DOOR TRIM-103, How to Build an Eared Architrave Part 1.
When Do I Not Use Plinth Blocks?
You can use plinth blocks on every single door surround in your home, or, if you want to subordinate door treatments, you can omit them in lesser rooms and only use them in public areas of your home like hallways, foyer, living and dining room.
Learn more about Architectural Subordination here.
Well that should get you started in the right plinth block direction.