Lime Putties

GLA DTG PUTTY can be made by adding enough linseed oil to whiting (pure finely ground chalk) to make a paste. After it has dried it can be sanded. LIME PUTTY is slaked lime and water mixed thickly and left to stand to form a smooth paste. 

Slaked lime is produced by reacting, or slaking quicklime with water, and consists mainly of calcium hydroxide. The term includes hydrated lime (dry calcium hydroxide powder), milk of lime and lime putty (dispersions of calcium hydroxide particles in water). Slaked lime is widely used in aqueous systems as a low-cost alkali. 

The process is called hydration and should be differentiated from slaking which involves the production of a dispersion of calcium hydroxide in water (i.e. a milk of lime or a lime putty, see chapter 22). However, the expression slaked lime is used as a generic term for hydrated lime, milk of lime and lime putty. 

Most commercial hydrated limes have median particle sizes, as measured by laser granulometry, of about 5 to 10 pm. Hydrated lime quality may also be assessed by testing either a milk or a lime putty prepared from the hydrate under specified conditions (see section 22.7.2). 

BS 6463, Part 4 Methods of test for physical properties of hydrated lime and lime putty , 1987. 

Lime putty is a thick dispersion of slaked lime in water. Putties typically contain 55 to 70 % by weight of solids. A semi-fluid putty is sometimes described as a lime paste . 

The production and properties of milk of lime and lime putty are important for two reasons. 

Although most of the parameters affecting the production of milks of lime and lime putties have been known for many years, much of the evidence was anecdotal and contradictory. It was based on microscopy and measurements of the bulk properties of the products. 

In recent years, the availability of laser beam granulometry has enabled a more fundamental approach to be adopted. This has lead to a better understanding of the parameters which affect the physical and chemical properties of milks of lime and lime putties and which, in turn, affect the suitability of the products for their various applications. As a result, products can now be tailored more precisely to the requirements of the customers processes. 

Lime putties are generally produced by allowing a milk of lime to settle and drawing off the layer of clear lime water. The settled solids are then mixed [22.4]. The properties of the putty improve with ageing and it is generally recommended that several hours be allowed between slaking and use [22.5]. 

The properties of lime putties improve progressively with time. They may be stored indefinitely under moist conditions. If left uncovered, a calcium carbonate crust forms that protects the putty from further carbonation. 

Performance Criteria for Milks of Lime and Lime Putties... 

The chemical activity and reactivity of milks of lime and lime putties are determined as described for hydrated lime in section 20.7.1. 

As a general rule, all milks of lime and lime putties should be de-gritted before use. EN 459 [22.6] permits up to 2 % of particles greater than 200 pm. 

The solids content of both milks of lime and lime putties is an important parameter, which affects their handling characteristics. 

The quality of building limes is specified in [22.6]. It requires minimum values for standard mortars produced from lime putties — namely penetration and air content — and lists water demand and water retention as parameters that customers may request. It also specifies a minimum volume yield of putty per kg of quicklime. Building limes must also be sound (i.e., pass the popping, pitting and expansion tests). A workability test, based on the spread of a standard mortar on a jolting table, was specified in the 1972 edition of BS 890 [22.11], but is no longer included. 

It should be noted that the physical properties of all lime putties improve on maturing. This is particularly marked when using hydrated lime, which should be matured as specified (generally for 24 hours). Milling milks of lime (e.g. in a colloid mill) also improves physical properties and accelerates the maturing process. 

Handling and Storage of Milk of Lime and Lime Putty... 

Lime putty is widely used as a component of mortar for masonry, rendering or plastering. It may be produced from either slaked or hydrated lime and made on site [23.2], or in a factory. In many countries, the latter option is becoming increasingly popular. In either case, the handling and storage requirements are similar. 

Hydrated lime, lime putty and milk of lime absorb carbon dioxide from the atmosphere. Their exposure during sampling, sample preparation and storage should, therefore, be kept to a minimum. 

Spot samples of milks of lime and lime putties should be sampled as described in EN 459-2 [24.2], This requires a sufficient number of increments to be taken to give a spot sample of (10 5) 1. 

Category 1 building lime — hydrated 2 building lime — putty 3 hydraulic building lime 4 high calcium quicklime — hydrated lime 5 high calcium quicklime — milk of lime 6 hydrated lime... 

Perhaps over 80 % of the quicklime produced, other than that used in steelmaking, is used either as a milk of lime or as a lime putty. For such apphcations, there are three main options, namely to ... 

The cement should comply with EN 197 [26.32] (N.B., high alumina cement should never be used with lime). Lime, in the form of quicklime, hydrated lime, or lime putty, should eomply with EN 459 [26.18] see section 27.6.7. 

In wet generators, the carbide is added to an excess of water and an impure milk of lime is produced. The milk may be used on site (e.g. for effluent treatment), or it may be fed to settling pits. The resulting lime putty, or carbide dough is then sold as an inferior grade of slaked lime (see also section 22.9). 

The protective measures for quicklime, hydrated lime, lime putty and milk of lime are more comprehensive than for limestone [34.2]. The eyes are particularly vulnerable to damage and adequate eye protection should be worn at all times when handling lime products. Hot lime putties and milks of lime require special precautions as splashes can burn both physically and chemically. 

The hands should be protected by gloves with a tight-fitting wristband. Breathable canvas or leather is suitable for dry conditions, but, where lime putty or milk of lime is being handled, waterproof gloves should be used. Any exposed parts of the arms, wrists and hands should be protected with barrier cream. 

Drowned lime is produced when lime is slaked in excessive amounts of water so that the temperature required for effective slaking is not produced. A skin of lime putty seals the surface of the particles and prevents further slaking. 

Fattening of lime putties is the slow absorption of water, which increases volume yield and plasticity. 

Lime putties are slaked limes mixed with water to a desired consistence, mainly consisting of calcium hydroxide with or without magnesium hydroxide. 

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