February 11, 2026 · 7 min read
Why lime plaster suits pre-war Boise houses
A great deal of Boise's North End and East End housing predates 1940. If yours does, the walls are almost certainly lath and plaster, and they were built on an assumption that modern materials quietly violate.
This is the most consequential thing on this entire site, and almost nobody explains it before selling you a finish.
Old walls were designed to get wet and dry out
There is no vapor barrier in a pre-war wall. There was never meant to be one. Moisture that gets into the assembly, whether from indoor humidity, snowmelt, or a sprinkler line too close to the foundation, passes through the plaster and evaporates away.
The whole system depends on the wall being able to dry in at least one direction. Lime plaster is vapor open, so it does not interfere.
What modern coatings do to them
Acrylic paints, vinyl wallcoverings, and cement-based finishes are far less permeable. Applied to an old wall, they slow or stop drying in that direction.
The moisture does not disappear. It accumulates in the assembly, where it reaches the lath and the framing. The damage happens out of sight, which is why people usually do not discover it until it is structural and expensive. The surface can look perfect the entire time.
Why lime is the technically correct answer
Lime plaster is slaked limestone, aggregate, and water. It stays vapor open permanently, so the wall keeps working the way it was designed to.
It also carbonates, meaning it slowly reabsorbs carbon dioxide from the air and hardens toward stone over years. Roman lime plaster is still on Roman walls. That is not marketing; it is the reason the technique survived.
And its high pH makes it inhospitable to mold, which matters in any bathroom or kitchen regardless of how dry the climate outside happens to be.
The honest trade-off
Lime is the softest finish we apply. It marks. A dragged chair, a scrubbed splash, or a dog leaning on the same spot will show, and some of it will stay.
In a busy kitchen or a hallway with children it will look worn within a couple of years. Some owners of old houses want precisely that patina. If you do not, put microcement in those rooms and keep lime for the rest.
How to tell what you have
Press a thumbtack into an inconspicuous spot. Drywall takes it easily; plaster resists. Tap the wall: plaster over lath sounds solid and slightly hollow in a rhythm matching the lath spacing.
If you are unsure, we can tell you in about a minute during a consultation, and the answer changes what we recommend.
In short
If your Boise house is pre-war and still on original plaster, breathability is not a preference. It is building science, and lime is the material that respects it.
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