#667 Our Gypsum Lath Surprise

Our Ozarks bungalow was built in 1914, the heyday of finishing interior walls with lath (thin wooden strips nailed to the framing) covered with several coats of smoothed wet plaster. The wet plaster oozed between the lath to form 'keys' which hardened as they dried, locking the plaster to the wall. You can imagine this was not something 1914 homeowners took on as a weekend do-it-yourself project.  It took a lot of time and skilled labor to install lath and plaster.  Here's a behind-the-scenes peek at one of our lath and plaster walls where you can see the vertical wall studs, horizontal lath, and oozing plaster keys frozen in time since 1914. 

So I was both surprised and puzzled when I opened up one of our interior walls and found no lath, no plaster, no oozing, no keys, but instead this:

What's up here?  From the back, this wall looks to be covered with modern drywall, clearly not from 1914.  But it's odd that each drywall strip is only 16" wide. My first thought was the wall had been remodeled and I had found where a drywall crew used up their scrap.  But upon closer inspection, I saw the drywall strips have two factory-finished edges.  So they were not field-cut scraps.  They were created as 16"-wide strips at the drywall factory.  Hmmm.

Take a close look at the photo for more clues.  The wall shows ghosts of a previous lath-and-plaster wall.  See the gray horizontal lines on the framing boards spaced at the same width as lath?  That's where the wet plaster originally oozed between the now-missing lath. The vertical studs show a pattern of two nail holes where each lath was attached.  So at one time, this wall too was covered in authentic 1914 lath and oozing plaster.  But then what happened?  Why remove the lath and plaster?  Once removed, why would a builder use 16"-wide drywall strips rather than full 4'-wide sheets to rebuild the wall?  Hmmm.

About the time we were sleuthing our walls, I was pleasure reading Norm Abram's book Norm Abram's New House and came across a paragraph Norm wrote just for me:

By the time my father built his house, the system had evolved into fastening panels of rock lath (a rigid gypsum core with a paper covering) that were sixteen by forty-eight by three-eighths of an inch thick to the studs and then applying about three-eighths of an inch of plaster: a base coat of brown plaster and then a finish coat of white plaster or plaster tinted to the desired color of the room.

Of course I fact-checked Norm with a specimen sliced from our own wall.  In the photo below, there's our 3/8" thick gypsum lath at the top layered with multiple coats of seamless plaster to form nearly an inch-thick wall surface just as Norm described.

Combining this revelation with other more visible clues, we've concluded our house underwent an extensive remodeling in the 1950's when builders were in an extended period of transition converting over from the old-school labor-intensive lath-and-plaster approach to the speedy modern drywall. As part of that 1950's remodeling, most of our original 1914 lath and plaster was ripped out and replaced with then-popular hybrid gypsum lath. 

Surprise. Ours is a 1914 Ozarks bungalow with mid-century gypsum lath walls.

Yours in wall sleuthing,
Kelly