by Randy Ruth of LimeWorks.us

1. HISTORIC MORTARS:
THE CHEMISTRY BEHIND
WHAT BINDS OUR BUILT
ENVIRONMENT

2. What is mortar?
 A mixture of various compounds including Lime and
or Cements mixed with water and sand to bond or
cover Masonry i.e. brick, stone, terracotta, stucco, and
plaster.
 Mortar ≠ concrete or cement

3. Historic mortars
 Historic mortars
 Gypsum
 Great pyramids in Egypt
 Interior plaster
 Stone mortar
 Lime
 Primary building binder for
3000 years
 Natural Cement
 Portland Cement
 Recent applications 1824
England and 1870 in U.S.

4. Types of historic lime mortars
• Air Lime Cycle
 Three basic types
 Hi-calcium Lime
 Dolomitic Lime
 Magnesium Lime
 Hexagonal plate
crystal structure
 Sets Via
Carbonation
 Impurities can
produce hydraulic
behavior
 Burned @ 950 F

5. Types of historic lime mortars
 Natural Hydraulic lime
Cycle
 Two basic types
 Argillaceous
 Clay impurity
 siliceous
 Pure Silica
 Hexagonal plate crystal
structure
 Sets Via Carbonation
 Set Via Hydraulic reaction
with Silica
 Belite (di-calcium Silicate)

6. Types of historic lime mortars
 Pozzolanic Hydraulic lime Cycle
 Needs a reactive silica source
 Calcinated material
 Brick, tile, fly-ash, Blast furnace
slag, glass, silica fume….
 Must be the right fineness
 At least 180 microns
 Hexagonal plate crystal structure
 Sets Via Carbonation
 Set Via Hydraulic reaction with
Silica
 Belite (di-calcium Silicate)
 Varying minerals formed

7. Manufacture and mixing
techniques of historic mortars
• 3000 B.C. – Roman
Empire
 Limestone burned in
Ricks and stone kilns
 Most often mixed and
transported by hand in
baskets
 Primarily hot lime mixing
 Quicklime mixed on
site with sand
 Laid fresh
 Lime slaking for plaster
and washes
 Fresco

8. Manufacture and mixing
techniques of historic mortars
• Fall of Rome – 1700’s
 Vitruvious
 1 lime : 3 sand
introduced
 Quicklime not hydrated
lime
 Pozzolanic mix designs
for “Roman concrete”
 Mixed very stiff and
hand compacted
 Used vitrified clay
(tiles)
 NHL used in Europe
 “Roman Cement” lost
 Basic lime mortar used
and sourced locally

9. Manufacture and mixing
techniques of historic mortars
• 1700’s – 1870’s
 1759-John Smeaton- Builds
Eddy stone Lighthouse with NHL
+ pozzolan
 1796-James Parker- Patent for
artificial hydraulic lime, called
“Roman Cement”
 1818-Natural Cement found in
Madison county, NY
 1824-Joshph Aspdin- Patents
Portland Cement in England
 First cement to contain “Alite”
Tri-calcium silicate
 1868-First Shipment of Portland
Cement to U.S
 1871-First Portland Cement
Plant opens in Coplay, PA

10. Manufacture and mixing
techniques of historic mortars
• 1870’s – 1913
• 1880’s-experimentation
with rotary kiln
• 1896-first year U.S.
Portland cement
production exceeds
importation
• 1900-First year Portland
cement Production
exceeds Natural Cement
• 1904-1913 – Rotary kiln’s
become primary kiln
design
• Burned @ 2400 F

11. The debate has not changed
1914 article
in
”Engineering
News”

12. Manufacture and mixing
techniques of historic mortars
 1913-Present
 Modern Portland Cement
reigns in engineering
projects
 Slag Cement produced
 Lime fades as primary
binder around after WWII
 1:1:6 mix becomes
common
 Beginning of restoration
with high lime content
mortars in 1960’s
 Mid 1990’s – Beginning of
lime renaissance

13. Compare and contrast
Compressive strength
 The more hydraulic a mortar the greater its strength
 Lime mortars are slowest setting (carbonation &
belite)
 Portland cement is fastest setting (Alite and Belite)
 Pozzolans consume free lime to gain strength

14. Compare and contrast
Flexural strength
 The more free lime the
greater a mortars
flexibility
 High calcium and
Natural Hydraulic limes
have the most free lime
thus greatest flexibility
 Pozzolans consume free
lime to gain strength
thus reduce healing
ability

15. Compare and contrast
Vapor permeability

16. Question & Answers