How old should lime putty be?


Lime putty has been at the base of masonry construction for millennia. The Roman empire had mastered its use and with it built massive structures, many of which are still standing today. These structures are the living whitnesses and proof of the resiliant properties of lime putty in masonry construction. This knowledge was lost along with the fall of the Empire and remained buried for millennia. 

Pantheon in Rome

The Pantheon, a dome structure 140 feet in diameter, built around 27 BC in Rome, still remains the largest unreinforced cement dome structure in the world today. It has remained "in service" for over 2000 years!

Other well known structures such as the Colosseum in Rome, the Pont Du Gard in France, The Hadrian wall in the U.K. and many other impressive structures scattered throughout the Roman empire's reach are a testament to the superior qualities and longevity of lime putty based mortars for masonry construction.


VIRTUVIUS AND PLINIUS, THE ROMAN EXPERIENCE:

The unearthing and subsequent translation of original Roman manuscripts such as "DE ARCHITECTURA, Ten books on Architecture" written by  Marcus Viruvius Pollione, and "LA NATURALIS HISTORIA"  by Gaius Plinius Secundus, for the first time in over a thousand years finally shed some light in the formulation and use of lime mortars and the famed "Roman cement".  

These publications are currently available in English. 


THE THREE YEAR LAW:

The Romans instituted strict construction regulations laws during the rapid infrastructure expansion of the Roman empire.

These regulations arised from the necessity to implement safety standards for the fast paces development of the expanding urban centers with ever-taller and clusterd buildings so to minimize the possibility of collapse of poorly constructed structures.

Pertaining specifically to lime putty for producing construction moratrs and concretes, these regulations included:

forno romano

• The suitabilityof specific type of limestone for quicklime production, and preferred applications. 

• Design of lime kilns for producing qualitative quicklime.

• Procedures for slaking quicklime into lime putty.

• Correct storage of lime putty.

• Minimum aging requirements of lime putty for construction use.

Comparing these "rules" with modern studies on the properties of lime putty and mortar tests show that the Romans were indeed on target.


MODERN CHEMISTRY:

Recent studies and modern testing have shown that slaked lime's crystalline size and structure changes through aging, and continues to do so indeterminately.  These studies show that the crystalline structure of lime putty undergoes marked changes in shape from prismatic to tabular through aging. These changes have a beneficial effect on cohesion and adhesion in stucco and plaster work. When the mortar is applied, smoothed out or compressed, these platelet-shaped crystals line up in a flat overlapping fashion, much like fish scales, and ceate a strong cohesive bond.  The crystals size distribution also changes from an "evenly-sized" micronic crystal distribution to a more varied size distribution comprised of crystals of micronic and nanometric sizes, increasing adhesion and mechanical properties.  

In aged lime mortar carbonation also proceeds at a faster rate and occurs from the extremities of the body of the mortar towards the core center. These behaviour has been confirmed by modern testing referred to as the "Liesegang Rings" 

The carbonation processin in mortar made with fresh lime putty only starts at the surface exposed to the air and slowly moves deeper into the masonry work. 

Aged lime has higher water retention properties, aiding in a slower curing of the mortar and a faster set. 

Through the morphological changes in aging slaked limes, crystals of large, medium and small sizes are formed and the aged lime develops a higher viscosity. This is extremely beneficial as it allows for a workable mortar mix without, or with limited water addition and also for a higher binder ratio. This in turn minimizes shrinkage and INCREASES FROST RESISTANCE.

Aged lime putty is not hard on pigments and will maintain the color of pigments unaltered overtime. 

Hard limestone and soft limestone varying in magnesium content and christalline size produce lime putties with different properties which makes them more suitable specific purposes. 

A hard white marble with large crystals would produce a leaner putty more suitable for laying masonry units and a soft limestone with fine crystals would produce a fatter lime more suitable for stucco or plaster finishes.


HYDRATED BAG LIME, NHLS AND PORTLAND:

It is A FACT that the larger crystalline structure of hydrated limes (bag lime) remains unchanged even when turned into a paste and left to age for long periods of time. Modern hydrated limes are suitable as a plasticizer in Portland cement mortars.

Quicklime,Hydrated lime, and Portland cement (any lime or cement in a quicklime or dry powder form) begins to carbonate and deteriorate the moment it is produced. Even intact unopen bags which have been perfectly stored will have a 6 month shelf life from the day they were produced. Open bags should be used within three days or discarded. This is because the quicklime, lime or portland cement begins to absorb moisture and carbon dioxide from the air and a chamical reactions is slowly taking place. Given the fact that NHLs are imported from Europe, there is a major delay from the time they get produced, arrive at the the importer, then to the distributor, and finally to the end user, which very well may translate to several months. Chances are that the bag of NHL you are buying for your first job in the spring is likely to be a heldover bag from the leftover fall stock. The manufacturers refuse to print a date of production on their bagged products for this very reason.

Slaked limes, on the other hand only get better with age. Raw pozzolans also do not deteriorate.

With slaked lime, sand and pozzolans you can be 100% sure that carbonation and hydraulic reaction will begin taking place only at the very moment of mixing and use.

          

Here are some parameters for choosing which of our high quality Italian Lime Putty is best for your specific job: 

Crema di calce: (cream of lime)

This lime putty is produced by slaking a hand selection of the whitest quicklime lumps, aged in open air pits and micronized prior to packaging.

Micronized lime putty aged 24, 36, 48 months or more:

Fine Stucco and Plaster finishes, Marmorino, Venetian Plaster, Scagliola, fresco, lime paint, restoration work.

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Grassello: (fatty lime)

Italian Lime putty aged 12 to 24 months: 

NEW CONSTRUCTION, stone and brick bedding mortar, scratch and brown coats, plaster and stucco, age for future use. 

Lime putty aged 24, 36, 48 months or more: 

RESTORATION WORK, stone and brick bedding mortar, repair and repointing mortar, scratch and brown coats, plaster and stucco,.

IMPORTANT !

GRASSELLO MAY CONTAIN SOME PARTICLES OF DEHYDARATED LIME!!! 

Occasional small pieces of "dried up" lime inevitably fall off the equipment which transfers the slaked lime from the vats into the buckets, A VERY MESSY BUSINESS!  This is a testament of the ARTISANAL production of our lime putty and these particles are in no way detrimental to the performance of our lime putty. These "lime aggregate particles" are actually WELCOME in restoration where they resemble the underburnt/over burnt lime particles often present in the original lime mortars.

AGED GRASSELLO can be FILTERED in order to be used for lime paint, fresco, restoration work and fine plaster finishes.


CALL US FOR MORE INFORMATION!    We will be happy to answer any of your question!







© fabio bardini 2012