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It’s a Mystery

Take a guess what this item is (shown below).

Plaster

Looks kind of hairy and gross, doesn't it?

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Does this help?

I'll give you a hint. It was found inside a 1920s home.

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This should help you figure it out.

This should help you figure it out.

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This pretty well gives it away.

This pretty well gives it away.

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In fact, its a chunk of plaster that was cut out of a wall.

In fact, it's a chunk of plaster that was cut out of a wall to add a new outlet.

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Up until sheetrock became widely accepted, a home’s interior walls were finished with plaster. Today, the word “plaster” is used loosely to describe any gypsum-based wall covering, but in fact, plaster is fairly unusual in post-WW2 homes and quite rare in post-1980s homes.

If you look at an old Sears catalog, you’ll find that while kit houses did not include plaster (due to shipping weight), your 12,000-piece kit house did come with good quality lath. In fact, the “Chelsea” (a 2,000-square-foot foursquare) came with 840 square yards of wooden lath. Sears estimated that a plasterer would charge you $200, which included nailing up all those thin strips of lath and applying three coats of plaster (1916).

Often, people talk about “old-fashioned horse-hair plaster,” but the binding agent in old plaster walls was more commonly cattle hair.

Plastering is fast becoming a lost art, and things have changed a bit in the last many decades. Today, a wire mesh is used in place of wooden lath. And I’m not sure what the contemporary binding agent is, but I seriously doubt it involves shaving dead cattle. However, you can still find good recipes online for making historically appropriate plaster to restore or repair the walls in your old house.

Old plaster walls ahve three coats: The scratch coat, the brown coat and the finish coat.

The scratch coat gets its name from the fact that it is scored so that the surface has a rough texture. This rough texture gives the brown coat (which contains a lot of sand) something to grip.

It’s the sand in the brown coat that helps the finish coat (which is about 1/8″) bond tightly to the walls.

According to the smart people, the scratch coat and brown coat are about 3/8″ thick, but the image shown above (from the 1920s house) tells a slightly different story. Making and applying plaster was a little bit like baking a cake: A lot depended on the cook, and his preferences and practices.

Plus, sometimes the “cook” was sober as a judge and sometimes the “cook” was so plastered (perhaps the source of the term?) that he couldn’t walk a straight line. Weather, humidity and quality of ingredients were other variables that affected the final product as well.

As always, if you have any thoughts to share, please leave a comment below!

To learn more about Sears Homes, click here.

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This promotion, which appeared in a 1916 Sears Building Materials catalog, gives a pretty good explanation of how plaster was applied. I can't imagine how long it took to nail up all those lath boards (which were typically 1-inch wide). And the smudge pots were used to keep the temperature and humidity at a certain level while the plaster dried. Making and applying plaster was a slow, arduous process with many variables (1916 Sears Building Materials).

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By 1916,

By 1916, "Sheet Plaster" had already gained a toe-hold in the market, but it wasn't until after WW2 that it really became popular. And yet even in modern custom-built homes, plaster walls are considered an upgrade (and they're mighty expensive, too). My 1962-built ranch has sheetrock walls and plaster ceilings, which seems an odd combination (photo is from 1916 Sears Building Materials).

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Sheet

As shown in this 1916 Building Materials catalog, "Sheet Plaster" was much easier to install.

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To read a *fascinating* article about the benefits of old plaster walls (and how it was made), click here.

Bob Vila drives me to hard liquor, but his writers did put together a nice piece on plaster. You can read it here.

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  1. Valerie chochla
    February 14th, 2014 at 11:15 | #1

    Thanks, this is very interesting! Almost makes me want to cut a piece of my wall out.

    Just kidding!

  2. Charles
    February 15th, 2014 at 03:19 | #2

    Excellent material, as usual. Thanks.

  3. March 13th, 2014 at 06:36 | #3

    “Plastering is fast becoming a lost art”, quite true, contemporary binding agents do not last long, especially the most marketed one.

    Making a historically appropriate plaster is the most recommended to repair and restore an old wall, however, the question is where will we get the manpower and materials?

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