Dampproofers

Table 6. Coal-Tar Pitch Used in Roofing, Dampproofing, and Waterproofing ...

Coal-tar pitch for other uses is similarly subject to a few national specifications but mainly sold to users specifications. Pitch intended for roofing, dampproofing, and waterproofing is the subject of ASTM specification D450 and Federal specification R-P-381 hot-appHed tar-based coatings (pipeline enamels) are the subject of BSS 4164/1987, amended in 1988, and, in the United States, of American Water Works Association (AWWA) specification C203. 

Coat the interior and exterior of the wall with dampproofing. 

The application of dampproofing and waterproofing materials on the exterior, interior, or both sides of the foundation that can serve as a radon-resistant barrier is recommended to help control radon entry. It must be understood that a coating applied to a foundation intended to resist the flow of radon into the building is in addition to the normal waterproofing/dampproofing requirements. 

If waterproofing or dampproofing treatments that are effective gas barriers and that can be sealed at joints and penetrations could be identified, then walls could be made radon resistant. Acceptable dampproofing or waterproofing treatments are specifically listed in building codes in many areas of the United States these lists are periodically amended as new materials come into use. These coatings apply primarily to basement walls. 

The most common dampproofing treatment for residential foundation walls is a parge coat covered with bituminous asphalt. The parge coat is used for concrete masonry walls but is not necessary for poured concrete walls. This two-stage treatment has been replaced by surface bonding cement in some areas. 

Surface bonding mortar or cement is mentioned in some building codes as an approved dampproofing treatment, but not as a waterproofing treatment. A number of manufacturers produce cements and mortars impregnated with fibrous glass or other fibers. Some of these may be chemically unstable in the alkaline environment of Portland cement. 

Dampproof walls (interior as well as exterior on masonry walls). 

Concrete dampproofers are integral admixtures that alter the concrete surface so that it becomes water repellent, or less wettable . This is illustrated in Fig. 4.1, which shows a close up of a water drop on a surface of a concrete that has had a dampproofer incorporated into it. This water repellency conferred on the concrete is only effective in preventing water from entering the surface when the applied pressure is small, e.g. rainfall in windy conditions, or capillary rise. The latter effect is shown in Fig. 4.2. In view of this, these materials are used normally for improving the quality of concrete pavers, tiles, bricks, blocks and cladding panels where the additional benefits of reduced efflorescence, the maintenance of clean surfaces and the more even drying out of adjacent bricks and panels are also obtained. 

Fig. 4.1 Dampproofed concrete exhibits a high contact angle to water.

Fig. 4.2 Dampproofed concrete bricks exhibit aimost no capiiiary rise. 2A = Dampproofed. 2 = No dampproofer.

In water-retaining structures or basement concrete subject to high hydrostatic pressure, materials of this type are generally not beneficial. However, some dampproofing admixtures do contain water-reducing admixtures and will result in a reduction in permeability under an applied hydrostatic head. In addition, the reduced capillary size and quantity will increase the hydrostatic pressure required to enter the concrete surface (see later). 

The chemical materials used to produce dampproofers are able to form a thin hydrophobic layer within the pores and voids and on the surfaces of the concrete in one of three ways (1) reaction with cement hydration products ... 

Dampproofers based on liquid fatty acids, such as oleic, caprylic and capric, are used as major components in fatty-acid mixtures. A typical example is shown in Table 4.2 [3]. The mixtures are added directly to the concrete mix without predilution, or addition to the gauging water. 

Table 4.2 Typical composition of liquid fatty acid dampproofers ...

Certain vegetable and animal fats have been used as dampproofers and again emulsions or pastes are preferred and typical formulations are given in Table 4.3 [10]. The fat can be white grease, tallow or soya bean oil and although they all produce hydrophobic concrete, different effects on compressive strength are obtained. 

Very finely divided wax emulsions are effective concrete dampproofing agents and are formulated so that the emulsion breaks down after contact with the alkaline concrete environment and forms a hydrophobic layer. 

This type of dampproofing admixture is widely used in the concrete products industry, in particular the calcium and aluminium stearates. The calcium stearates can be produced by grinding stearic acid with lime or cement to produce a material containing 10-30% calcium stearate. 

Table 4.4 Typical characteristics of wax emulsion type of dampproofer...

There is not a great deal of published data on the effect that dampproofing admixtures have on cement pastes in the way that water-reducing and air entraining agents have been studied, but some observations can be made. 

Addition of dampproofers based on caprylic, capric or stearic acids, stearates or wax emulsions do not have any effect on the setting characteristics of hydration products of Portland cement. However, the unsaturated fatty acid salts, such as oleates, although not affecting the tricalcium silicate hydration, have a marked effect on the ettringite and monosulfate reaction [12] and this is illustrated in the isothermal calorimetry results in Fig. 4.4. It is possible that a calcium oleoaluminate hydrate complex is formed involving the double bond of the oleic acid. 

It is believed that in the presence of dampproofing admixtures, the surfaces of the concrete, and the internal surfaces of the pores become coated with either a layer of molecules in the case of stearic acid and other fatty acids (Fig. 4.5b) or a layer of coalesced or separate particles of material in the case of waxes and bitumens, etc. (Fig. 4.5c). The end result in both cases is the production of hydrophobic surfaces exhibiting high contact angles to water, as shown in Fig. 4.6. 

Fig. 4.5 The molecules or particles of the dampproofing admixture line the capillaries with a hydrophobic sheath.

Dampproofed concrete, therefore, should not show significant uptake of surface water in conditions of rain and wind up to about 100 km h T In fact, on prolonged exposure, some wetting does occur, because of defects in the hydrophobic coating, and the presence of larger voids in the concrete, up to perhaps 1 mm wide these are due to incomplete compaction, or to the nature of the concrete in the case of blocks. 

Dampproofing admixtures are formulated to affect the properties of the hardened concrete, and not those of concrete in its plastic state. In the case of materials based solely on calcium and aluminum stearates, stearic acid in solid or emulsion form, bitumens and hydrocarbon resins, there will be no effect on the properties of the plastic concrete with regard to air content, workability, mix design parameters, etc. When water-reducing admixtures or accelerators are included in the formulation, the effect on the concrete will be a function of the particular type of material used (see relevant section). The wax emulsions do appear to have an effect on the properties of the plastic concrete because of the lubrication effect of the very small... 

Table 4.6 Effect of a wax emulsion type of dampproofer on the compressive strength of concrete of varying cement content...

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