**2. Masonry materials**

#### **2.1 Historic masonry units**

#### *2.1.1 Natural stone*

Stone has been used from earliest times. Stone as a material is geographically widespread. Its use in structures is often confined to local materials from a nearby quarry. Load bearing stonework was used up to about the late nineteenth century, but many earlier structures were built of rubble or brick faced with stone ashlar. Since about the year 1900, stone has been mostly used as facade to cheaper masonry or as cladding for other materials.

Stone masonry construction may be of ashlar, squared/coursed rubble, random rubble, etc. Composite rubble/ashlar walls have often been used. It cannot be assumed that a pier or wall with ashlar facing is of solid construction through its entire section; often the core will be of very weak material [5].

### *2.1.2 Bricks and blocks*

Bricks are the oldest man-made building material. Examples of sundried clay bricks (adobe) date back to 8000 BC, and fire bricks were used by 2500 BC. Clay bricks were traditionally made locally. Urban buildings of the late nineteenth century and early twentieth century were made of masonry of fired ceramic bricks [5]. In the transition to the use of steel, concrete constructions appear, which employ hybrid metal profiles for supporting floor slabs or as bridges and columns within the masonry to withstand earthquakes known as sidero-brick [6]. Since 1930 the use of reinforced concrete in the world is

widespread, leaving the brick masonry walls for minors or cladding in reinforced concrete structures or termination of facades.

Although features may be more reliable as a dating aid, brickwork may sometimes be approximately dated by the brick size. However, there are regional variations which may be greater than those relating to age [5]. Bricks can be fired clay, calcium-silicate or concrete.

**Figure 3** shows different placement patterns of solid bricks: stretcher bond, header bond, English bond and Flemish bond, which have different applications in construction (walls, landscaping, pavements).

These patterns allow to identify the time of construction but not the elements of metallic union that were placed from the middle of the nineteenth century in the form of flat strips every four or six courses. Its presence is detected by the slight but regular cracking in these joints due to the increase in volume due to iron corrosion.

The walls with inner cavities are later than 1850 for thicknesses close to 0.40 m and preponderance from 1930 to thicknesses of 0.45 m. These walls generally have a common brick course, an air layer of 0.05 m and a course of decorative purposes or tightness control.

The first uses of concrete blocks are at the beginning of the twentieth century with an important growth due to the demand of houses before World War II. Since World War II, the use of concrete blockwork increased dramatically because of the promotion of cavity walls and the need for improved thermal insulation, which was achieved by the use of lightweight concrete blocks for the inner skin.

Block sizes vary from 390 × 190 × 60 mm to 590 × 215 × 250 mm. The blocks may be solid, cellular or hollow. Densities vary in the range 475 kg/m3 (autoclaved aerated) to 2000 kg/m3 (normal aggregate).

#### **2.2 Historical binders**

The mortars present in the historic masonry of buildings are typically composed by simple or hydraulic limes. There are two kinds of binders, aerial or hydraulic, depending on the mechanism of hardening [7].

They can be subdivided into simple mortars, hydraulic mortars and composite mortars. The binder can be cement, lime or mix of both. In the past, same mortars contained ash to give a dark colour.

#### **Figure 3.**

*Common solid brickwork bonds: stretcher (up, left), header (up, right), English (down, left) and Flemish (down, right) bonds [5].*

**59**

*Historic Masonry*

into the mortar.

and soundproof.

water ingress into the wall.

mortar samples taken from the joints.

*DOI: http://dx.doi.org/10.5772/intechopen.87127*

friction and the staggered pattern of the bricks.

stone or brick and on the thickness of the wall.

supplemented subsequently by carbonation of any free lime.

go through the stones or bricks rather than follow the joints.

sion, tension and flexure but not to a great degree.

**3. Historical masonry construction techniques**

The function of the mortar is to hold together the masonry units and compensate its dimensional tolerances. Also the purpose of mortar is to transfer the gravitational force uniformly through the brickwork, the tying effect being achieved by

Pure lime mortars, containing no clay or silt, are hardened by carbonation of calcium hydroxide. This can take many years, depending on the porosity of the

In the case of mortars made from hydraulic lime, where the limestone is ground and fired with some clay or silt, the lime reacts with water for initial strength gain,

Pure lime mortars (lime-sand) are relatively weak and flexible. Pure cement mortars (cement-sand) may be stronger and stiffer than the stone or brick. If the mortar is too strong, any cracks in the masonry from whatever cause may therefore

Cement-lime mortars (cement-lime-sand) have intermediate strengths; the greater the proportion of cement, the stronger the mortar. Small additions of cement to lime mortars increase the strength marginally but reduce the permeabil-

Mortar joints are eroded by rain running down faces of walls. This effect is aggravated by chemical breakdown of the binder, because of the acidity of the rainwater. The resistance to this weathering increases with the total proportion of binder to sand. Sulphates, from whatever source, can cause the expansion and disintegration of mortar. Some bricks contain sulphates which may be leached out

The strength of the mortar influences the strength of the masonry in compres-

Lime-sand mortars were traditionally used. They were able to accommodate movement, both from the bricks themselves and from the structure as a whole. It was considered a good practice that the mortar should never be stronger than the

Strong cement-rich mortars tend to shrink, which can lead to poor bonding and

The basic method of construction has barely changed in several thousand years: the units are placed one above the other in such a way that they form an intertwined assembly in at least two horizontal directions. Sometimes order is achieved in the third dimension. Most of the time, an intermediate layer of mortar is used to save small to large inaccuracies between units and make the walls waterproof, airtight

The compressive strength of mortar in existing joints cannot be measured directly. The ratios of cement/lime/sand can be established by chemical analysis of

brick. This must be taken into account when specifying the repair mortar.

There are four main techniques for achieving stable masonry [8]:

mortar or with very thin joints (e.g. ashlars or thin-joint).

1.Irregularly shaped and sized but generally laminar pieces are selected and placed by hand in an interlocking mass (e.g. dry stone walls, see **Figure 4**).

2.Medium to large blocks are made or cut very precisely to one or a small range of interlocking sizes and assembled to a basic grid pattern either without

ity significantly. This can result in frost damage in porous stone or brick.

#### *Historic Masonry DOI: http://dx.doi.org/10.5772/intechopen.87127*

*Heritage*

calcium-silicate or concrete.

tightness control.

aerated) to 2000 kg/m3

**2.2 Historical binders**

widespread, leaving the brick masonry walls for minors or cladding in rein-

Although features may be more reliable as a dating aid, brickwork may sometimes be approximately dated by the brick size. However, there are regional variations which may be greater than those relating to age [5]. Bricks can be fired clay,

**Figure 3** shows different placement patterns of solid bricks: stretcher bond, header bond, English bond and Flemish bond, which have different applications in

These patterns allow to identify the time of construction but not the elements of metallic union that were placed from the middle of the nineteenth century in the form of flat strips every four or six courses. Its presence is detected by the slight but regular cracking in these joints due to the increase in volume due to iron corrosion. The walls with inner cavities are later than 1850 for thicknesses close to 0.40 m and preponderance from 1930 to thicknesses of 0.45 m. These walls generally have a common brick course, an air layer of 0.05 m and a course of decorative purposes or

The first uses of concrete blocks are at the beginning of the twentieth century with an important growth due to the demand of houses before World War II. Since World War II, the use of concrete blockwork increased dramatically because of the promotion of cavity walls and the need for improved thermal insulation, which was

Block sizes vary from 390 × 190 × 60 mm to 590 × 215 × 250 mm. The blocks

The mortars present in the historic masonry of buildings are typically composed by simple or hydraulic limes. There are two kinds of binders, aerial or hydraulic,

They can be subdivided into simple mortars, hydraulic mortars and composite mortars. The binder can be cement, lime or mix of both. In the past, same mortars

*Common solid brickwork bonds: stretcher (up, left), header (up, right), English (down, left) and Flemish* 

(autoclaved

achieved by the use of lightweight concrete blocks for the inner skin.

may be solid, cellular or hollow. Densities vary in the range 475 kg/m3

(normal aggregate).

forced concrete structures or termination of facades.

construction (walls, landscaping, pavements).

depending on the mechanism of hardening [7].

contained ash to give a dark colour.

**58**

**Figure 3.**

*(down, right) bonds [5].*

The function of the mortar is to hold together the masonry units and compensate its dimensional tolerances. Also the purpose of mortar is to transfer the gravitational force uniformly through the brickwork, the tying effect being achieved by friction and the staggered pattern of the bricks.

Pure lime mortars, containing no clay or silt, are hardened by carbonation of calcium hydroxide. This can take many years, depending on the porosity of the stone or brick and on the thickness of the wall.

In the case of mortars made from hydraulic lime, where the limestone is ground and fired with some clay or silt, the lime reacts with water for initial strength gain, supplemented subsequently by carbonation of any free lime.

Pure lime mortars (lime-sand) are relatively weak and flexible. Pure cement mortars (cement-sand) may be stronger and stiffer than the stone or brick. If the mortar is too strong, any cracks in the masonry from whatever cause may therefore go through the stones or bricks rather than follow the joints.

Cement-lime mortars (cement-lime-sand) have intermediate strengths; the greater the proportion of cement, the stronger the mortar. Small additions of cement to lime mortars increase the strength marginally but reduce the permeability significantly. This can result in frost damage in porous stone or brick.

Mortar joints are eroded by rain running down faces of walls. This effect is aggravated by chemical breakdown of the binder, because of the acidity of the rainwater. The resistance to this weathering increases with the total proportion of binder to sand. Sulphates, from whatever source, can cause the expansion and disintegration of mortar. Some bricks contain sulphates which may be leached out into the mortar.

The strength of the mortar influences the strength of the masonry in compression, tension and flexure but not to a great degree.

Lime-sand mortars were traditionally used. They were able to accommodate movement, both from the bricks themselves and from the structure as a whole. It was considered a good practice that the mortar should never be stronger than the brick. This must be taken into account when specifying the repair mortar.

Strong cement-rich mortars tend to shrink, which can lead to poor bonding and water ingress into the wall.

The compressive strength of mortar in existing joints cannot be measured directly. The ratios of cement/lime/sand can be established by chemical analysis of mortar samples taken from the joints.
