Stucco News

Questions and answers on Stucco and Plastering-- January, 2015


What is lime plaster?

What is lime stucco?

What is lime ?

Mythbuster: The myth I am trying to bust is that old lime and sand plaster is
not gypsum plaster which is super hard.
I worked for years on hospitals, schools, jails, government buildings, etc.
which required durable walls for resistance to abuse. In applications like hospitals,
cheap drywall is pound foolish. The basecoat plaster we used was "hardwall" or gypsum plaster
and sand. Lightweight aggregate such as perlite and vermiculite wasn't permitted because it is too weak.
The basecoat plaster you see at Home Cheapo (structolite or gypsolite) is gypsum plaster with
perlite premixed, just add water and stir.
This is for convenience for Handy Andy and Harry Homeowner, but is too weak to be used on
commercial work. The instructions on the bag even say it is not to be used on metal lath.
I didn't even mention that hardwall and sand is four times cheaper than pre-mixed plaster.
Holes in lime
                                  and sand stucco house in Arlington,
                                  Virginia
Sheathing is
                                  good shape on this 1920 wood lath and
                                  lime and stucco house
Mystic secret revealed !

On
most lime and sand stucco houses we work on
the sheathing and framing lumber is still in
good condition AFTER SITTING WITH GAPING HOLES FOR YEARS.

Sheathing is good shape on this 1920 wood lath
and lime and stucco house that had fallen into
disrepair over the years.
EVEN THE WOOD LATH WAS IN GOOD SHAPE
Note how our forefathers wrapped the window openings with homemade tarpaper, and left a gap between each sheathing board.

Lime and sand plaster almost always was reinforced with hair. This is referred to mostly as
horse hair plaster. Another Mythbuster: Hair used in lime and sand plaster was mostly pig hair,
cow hair and even human hair,. A couple of generations ago, back in rural America, animals were shaved
to prepare the skin for making leather. Farmers would accumulate this hair and sell it in the farmer's
market for use in lime plaster. Human hair from barber shops was also used. Hair was sold for plaster
in Richmond, Virginia up until the early 1950's.

Mel Gibson's great movie, Apocalypto, showed the Mayan Indians making lime, and plastering buildings
with lime plaster.
The Mayan method was inefficient. Limestone rocks were piled on firewood and heated, instead of
being heated in a lime kiln. This explains the mass deforestation in the Mayan empire. The trees were
used for making lime. The Mayans had an advanced construction industry, as shown by their buildings.

The ancient Romans discovered that by adding volcanic ash, or pozzolan, or brick dust, dramatically
increased the strength and water resistance of lime stucco and lime cement. The testimony for this
is the buildings and aqueducts that are still there. I went to an art exhibit at the National Gallery of Art
showing the art of Pompeii, and I was amazed that stucco frescoes were still in good condition
that had been under water and  and volcanic ash since 79 AD.

Ancient people in India and Egypt also discovered and used lime.

Even though Portland cement was invented in the 1820's, it wasn't used much in stucco until
the 1890's. Lime and sand was mostly used in stucco until about 1930, when almost all stucco
was Portland cement. Speaking from my own observation, I have only worked on
5 buildings built between 1890 and 1930 that had cement stucco. Everything else is lime and sand.
I have yet to work on a building built after 1930 that was lime and sand, all I have seen are
 cement stucco.

Deteriorated metal corner bead used in
                          stucco
From the job:
I took this picture at the job yesterday. This shows an observation that I have made. Note how the
1921 sheathing is still in good condition. Usually when we tear off lime and sand stucco, the sheathing and framing are in like new condition. Please note how our forefathers left a gap between the sheathing boards
to allow for building movement.
Inadequate coping deteriorates blocks in
                          Reston, Virginia   Another observation from stucco land:
Even though the metal lath isn't galvanized, there are
signs of corrosion but not bad deterioration.
Not bad after 90+ years.
This is due to the thickness, an honest 3/4".
When we find failure due to badly deteriorated lath,
the stucco was put on way too thin.


BTW: If you are wondering why the wall failed, the original copper flashing was put on backwards,
that is angled back to the wall, instead of away from the wall. The water infiltration after 90 years caused
the stucco to delaminate. Please read what I have to say about backwards flashing here and here.

Another Mythbuster: Ostriches don't stick their heads in the sand when they are scared.
The just run away like any other animal.