Traditional Plasters
Sympathetic with older walls
Traditional Plasters using lime are centuries old and still of
use today in older properties and wrongly regarded as
being outdated by the production of portland cement and
gypsum plasters. Lime plasters are commonly labelled
‘breathable’.
However, Modern Plasters and Renders can trap moisture
behind the wall if applied to traditional lime walls.
Modern Plasters can also break down the Lime cycle by
not allowing Carbon Dioxide to reach the lime mortar. This
can cause pointing, render and plaster to fail.
Types of Lime
Air Lime or Non-Hydraulic is a lime plaster that takes the
longest to set and cure and is considererd the most
appropriate for older buildings.
Hot Lime is very much a traditional product of a method
not commonly used today using Quicklime. Its likely your
home built a century ago used this method.
Natural Hydraulic Lime (not to be confused with Hydrated
Lime) comes in three strengths for interior and exterior
walls. NHL 2 being the weakest set, NHL3.5 and NHL5
being the strongest set. It sets without exposure to air,
therefore provides a faster set than Air Lime.
Hydrated Lime is often added to Portland Cement to
increase workability and make the cement more pliable.
If you’re home was built before World War II it likely
was originally built using Lime and therefore care and
consideration should be taken to choose the right
material in the long term.
Even after this date, houses were still being built using
lime materials, up until around the 1980s.
Other materials to look out for
Modern paints with silicone plastics can still bubble and
crack if moisture becomes trapped between the layer of
paint and a traditional plastererd or rendered wall. Even if
the manufacturer claim the paint is breathable damage
can still be caused if enough water is not released which
results in the paint being force off the surface by moisture
release. Heritage plasterers recommend limewashes and
silicate mineral paints or linseed paints to have maximum
breathability and allow moisture to escape. Claypaints are
recommended for interior decorating over lime walls.
Many original walls have lining paper/wall paper and this
does not stop the walls from breathing and protects the
plaster.
This book contains plenty of information to help you
make the right decisions in your period property.
Lath ceilings and cracks
Old lime and plaster ceilings attached to lath are notorious
for deep cracks. This is fairly common if the original
plaster is nearly a century old. It’s actually a testament to
traditional plaster if the ceiling can last a century with
only a few cracks, however its usually the plaster loosing
its grip to the laths that causes cracks.
Not to worry these cracks can often be repaired and
restored and will help in the preservation of your home.
The solution
The solution is to remove modern plaster that is causing
the failure of moisture to move freely, and to do this would
be to use the correct lime mortar plaster. The same is true
of exterior render/stucco.
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Lime Finish on Chimney Breast
Application of Lime Plaster
Sand and NHL3.5 Mix in Bucket
lime frieze restoration
Traditional Crack Repair