Footings and Special Bonds
FOOTINGS
The term footing is given to the courses of brickwork, stone or blockwork at the foot of a wall. The footing courses start immediately above the foundation and are laid flatwise. The rising wall is erected in the middle of the footing courses, so the footings, which are wider than the rising wall, project equally on both sides of the rising wall. If there is no wider concrete foundation, the combination foundation/footing is called a footing
PURPOSE OF FOOTINGS
Two main functions must be fulfilled by the footings;
They are the connecting link between walls and the foundation and act as an intermediate foundation for the walls, spreading the loads over a wider area of the concrete below.
They raise the floor level high enough above ground level to keep water out during the wet season.
FUNCTIONS OF THE FOOTINGS
Since the footings form the link between the rising wall and the foundation, the demands on them are similar to those set on the foundations. These are:
- To provide a solid, level base for the walls
- To receive loads from the structure above
- To distribute the loads onto the foundation (or the ground).
In addition, the footings have to:
- Raise the floor high enough above ground level to prevent moisture from rising through to the floor
- Keep the landcrete blocks of the rising wall dry.
As far as Rural Building is concerned the last function is the most important one.
HEIGHT OF FOOTINGS
The top of the foundations is usually at ground level, although they can be either above or below ground level depending on the subsoil.
When three footing courses are laid on top of the foundations, the soffit of the future floors will be 51 cm above ground level. This will meet the requirements of most situations.
If the building is in a valley, or in a place where the rain-water cannot run off quickly, the height of the footing courses must be increased.
MATERIALS AND MEASUREMENTS
The most common material used for footings is sandcrete blocks, laid flatwise in a half-block bond. The courses are 23 cm thick and 17 cm in height, and they are laid in the centre of the foundation strip.
In order to effectively prevent moisture penetration, three courses should be laid above ground level, thus raising the soffit of the floor to a height of 51 cm above ground level. This is the minimum for all bedrooms and living areas.
Only in cases where the building is not to be used as a dwelling place for people, for example a store or a shelter for animals, may the footings be built to a lower level.
The use of boulder or laterlte rock masonry is preferred as this can save considerable amounts of cement. The dimensions of such footings will be the same as those of sandcrete footings, when the laterlte rock blocks are cut to the same dimensions as sandcrete blocks.
COMPARE: 
Fig. 1 shows a building with no footing. The floor is at ground level and water can easily enter. The building in Fig. 2 rests on a footing and the floor is raised above ground level, so it will be drier and thus healthier to live in, and also less likely to collapse since the mud walls are kept drier.
SPECIAL BONDS
Special bonding problems occur at quoins, T-junctions and cross junctions where walls of different thicknesses meet. These situations are frequently found in connection with the footings. They may also occur in other masonry.
An example where footings with different thicknesses meet is in the construction of a verandah. This is because the footing courses under verandahs are laid edgewise instead of flatwise, in order to save material. This is possible because there are no great loads on the verandah footings.
The bonding problem arises from the fact that the dimensions of common sand-crete blocks make it difficult to form a bond between the edgewise courses and those laid flatwise. Fig. 1 shows that two courses laid edgewise do not exactly correspond with three courses laid flatwise: there is a 1 cm difference in height.
Footing blocks can be specially made to dimensions that will show a better correspondence, so that bonding is easier and less block-cutting is needed to make the bonds. Fig. 2 shows four flatwise courses of specially made blocks, 10,5 cm thick, which correspond perfectly with two courses laid edgewise. Thus bonding is made easier.
The verandah footing may be kept in line with the outside face of the wall footing (Fig. 3), or in line with the rising wall (Fig. 4) which results in a recessed footings.
Each type of block can be used with either a recessed footing or a flush footing. Therefore there are four possible situations:
- Common sandcrete blocks in a flush footing
- Common sandcrete blocks in a recessed footing
- Specially made sandcrete blocks (10,5 cm thick) in a flush footing
- Specially made sandcrete blocks in a recessed footing.
DIFFERENT WALL THICKNESSES AT A QUOIN
This situation occurs when a verandah is closed at one end with a wall, or where a "loggia" is made. A loggia is a room which has one side open to the courtyard, garden, etc. (Fig. 1). The footings which carry walls have to be regular flatwise footings, while the footing on the open side can be constructed with the blocks edgewise, since it does not carry any wall.
COMMON BLOCKS, FLUSH TO OUTSIDE:
Fig. 2 shows that both quoin stretchers of the edgewise courses (blocks A and C) have to be cut to an odd shape to fit together with the flatwise quoin header of the second course (block B). in order to maintain the half-block bond, block B has to be cut to a length of 39 cm.
SPECIALLY MADE BLOCKS, FLUSH TO OUTSIDE:
If specially made blocks are used, it is not necessary to cut them to odd shapes, and the bond is easy to make as well as more economical (Fig. 3).
A corner bond in which the edgewise courses are set back (recessed) in order to be in line with the outside of the rising wall does not make sense and it is therefore not shown here. It is best to apply one of the arrangements above, or to make the whole structure stronger by laying all the corner blocks flatwise (Fig. 4, below).
NOTE: It is best to avoid making these bonds with common blocks: use specially made blocks instead if possible, because it is extremely difficult to cut the odd shaped blocks (Fig. 2, blocks A and C) to the ideal shape without breaking them. If specially made blocks are not available, the common blocks can be given a wedge shape where they intersect, as indicated in Fig. 2 by the broken lines. This shape is easier to cut without breaking the blocks.
DIFFERENT WALL THICKNESSES AT A T-JUNCTION
In Rural Building we are mostly concerned with those T-junctions in which a course of edgewise blocks meets either a corner ("A" below) or a wall ("B" below) of flatwise blocks.
Situation "A" occurs for example when a verandah is built flush with the corner of the house; while situation "B" will occur if the verandah meets the wall of the house away from the corner,
There are also possible situations where a flatwise course meets a corner or wall of edgewise blocks, but these situations are not common in Rural Building.
Here we discuss four methods which can be used in situation "A", depending on the type of blocks available and on whether the edgewise course will be recessed or flush to the outside of the flatwise courses. Two methods are given to deal with situation "B".
SITUATION "A", COMMON BLOCKS, OUTSIDE FLUSH:
As with the corner bond using common blocks (previous page), this bonding problem can only be solved by shaping the first blocks of both courses of the thin wall so that the second course of the thick wall can be bonded (Fig. 1). This requires precise and careful cutting.
SITUATION "A", SPECIALLY MADE BLOCKS, OUTSIDE FLUSH:
Bonding becomes simpler and more economical when these blocks are used. Fig. 2 shows that there is no material wasted since the 1/4 block which is left from cutting the 3/4 block will be used in the fourth flatwise course.
SITUATION "A", COMMON BLOCKS, RECESSED:
This bond is almost the same as the first method above, except that the stretcher of the second flatwise course projects on both sides in the direction of the thin wall (Fig. 3, broken lines). After the mortar has set hard, the projecting corners are chiselled off,
SITUATION "A", SPECIALLY MADE BLOCKS, RECESSED:
In this case we can use the same bond as in the second method (Fig. 2). The 3/4 block and the full block above it have to be shortened by 4 cm. This will reduce the inside overlap of the junction, but that cannot be helped.
SITUATION "B", COMMON BLOCKS:
Again, here it does not make sense to talk about making a recessed thin wall: as at a quoin, the edgewise course will always be flush with the outside face of the flatwise footing course.
Fig. 1 shows that here again we find the same problem which always arises when common blocks are used in a bond between different wall thicknesses. The first blocks of the two edgewise courses have to be cut to odd shapes.
SITUATION "B", SPECIALLY MADE BLOCKS:
When this bonding method (Fig. 2) is compared with the last method, it is clear that once again the specially made blocks are the best choice.
DIFFERENT WALL THICKNESSES AT A CROSS JUNCTION
There are four possible situations for a cross junction with different wall thicknesses. The one which is described here is the most common in Rural Building. This situation occurs when the end of a verandah joins the wall of the house and is in line with an inside wall (Fig. 2, below). This means that the footing blocks are laid flatwise in three directions, and edgewise in one direction.
COMMON BLOCKS:
The first course of the thin wall is bonded into the thick one by a 3/4 block (block A) which must be shaped in such a way that the second course of the thick wall can overlap it (block B). Block A is followed on one of its stretcher sides by a 1/2 block, while all other directions are continued with full blocks (Fig. 1a shows the first courses).
In order to maintain the half-block bond, the second course of the thick wall must contain a block which is 18 cm long, and another 42 cm long; the latter overlaps the 1/2 block below. Don't forget that the first cross joint following the stretcher overlapping the thin wall is 3 cm wide, or else the first two cross joints are made 2,5 cm wide (Fig. 1b).
The third course of the thick walls is a repetition of the first one. The second course of the thin wall starts with a full block (block C) which is the same shape as the 3/4 block below it, so that it can be bonded into the thick wall. It is followed by the 1/4 block which was left over from the first course. Note that the thin wall remains 1 cm lower than the other walls, unless the mortar beds in the thin wall are both made 2,5 cm thick (Fig. 1c).
A disadvantage of this bond is that the overlap across the thin wall is rather short. This problem is not fully solved by using the specially made blocks.
SPECIALLY MADE BLOCKS:
The first course of the thin wall is bonded into the first two courses of the thick one by using a full block (block A). The first cross joint following this block is made 3 cm wide, or else the first two cross joints are made 2,5 cm wide. The first course of the thick walls continues with a 1/2 block (block B) in the direction of the thin wall, and with a 1/2 block (block C) either to the right or left side of the cross. The second course of the thick walls starts with full blocks where there are half-blocks below, and with a half-block which is above the full block of the first course (Fig. 1a).
The third course of the thick walls starts with a full block (block D) covering three cross joints. A block of 16 cm in length is placed beside this, above the full block; and a block of 40 cm length is placed on the other side, above the 1/2 block. The second edgewise course and the fourth flatwise course consist of full blocks, with the exception of a 3/4 block (block E) overlapping the 16 cm block below by 10 cm (Fig. 1b).
This cross junction bond, even with the use of the specially made blocks, still does not provide a very good overlap.
STAGGERED BOND WITH SPECIALLY MADE BLOCKS:
A simple but good masonry bond can be achieved by staggering the bond. This means that the thin wall is shifted to either side of the crossing thick wall. The distance between the two centre lines of the walls will be about 19 cm (Fig. 1a).
The first course of the thin wall is bonded into the thick one by using a full block. The two courses on the left side of this almost form a quoin, while the courses on the other side are completed in the normal way. Apart from the 1/2 block in the second course, only full blocks are needed (Fig. 1a).
The third and fourth courses of the thick wall are bonded as if in a T-junction, except that the 1/4 block of the third course is placed further away from the junction, to avoid having too many cross joints in the junction area (Fig. 1b).
NOTE: By planning ahead and doing a little extra work in setting out, you can avoid complicated and costly constructions.
For footings where there will be junctions between flatwise and edgewise blocks, it is always better to use specially made blocks which .are 10,5 cm thick. These allow proper bonding, are more economical, and avoid the necessity for constructing junctions between two edgewise courses and three flatwise courses.
Cross junctions between different wall thicknesses should be avoided because the bonding is difficult and the overlap is poor. A staggered bond is preferred in those cases where a simple T-junction cannot be made instead of the cross junction.
