Floor Construction

It is best to construct the floor after the roof covering has been completed. This makes it easier to crre the floor without problems caused by the concrete drying out too quickly and cracking.

Floors are constructed on top of the hardcore filling. There are two methods for floor construction used in Rural Building: one-course work and two-course work. One-course work means that the floor is made in a single layer; while in two-course work the floor is constructed in two layers, the base layer and the floor screed or finishing layer.

ONE - COURSE WORK

This means that the final surface finish is completed before the base layer has set hard. The result is a monolithic floor construction; which means that the floor throughout can be considered as one solid mass (Fig. 1). The advantage of this method is the short construction time, using a minimum of materials, and no separation between the top layer (screed layer) and the base layer.

TWO - COURSE WORK

This means that the base layer and the finish layer are constructed separately. After the base layer has set. hard, a floor screed is applied. This is a fine-grained mortar layer, about 2 cm thick, laid to finish the floor surface (Fig. 2).

The advantage of this method is that any faults in the base layer, such as cracks, can be covered. However, it takes longer to construct and requires more cement. Another disadvantage is that it can be difficult to get a good connection between the base layer and the floor screed. The base layer should be carefully treated with cement and water to form a good connection between the floor screed and the base layer.

CASTING METHODS

If a floor area is larger than approximately 10 square meters, the area should be divided into bays for concreting. A bay is one of several uniform divisions of a concrete floor which are cast at any one time.

The bays are separated by edge boards, which are laid and levelled to the required floor thickness. The edge boards act as a guide for the strikeboard to level off the concrete surface, therefore they must be laid and levelled with great care.

On the drawing below you can see the positions of the edge boards when the floor is divided into six bays. The boards should be arranged as shown so that the corners of the concrete bays will match each other when the floor is complete.

The division of the floor into bays helps to prevent the development of cracks due to shrinkage during the hardening process. The smaller the area, the less the shrinkage, and the fewer cracks will appear. Square-shaped bays are the best because all the sides will shrink by the same amount.

Bays also make the construction process easier. The bays are small enough to be cast, levelled and finished within a manageable time. The work can be interrupted to allow the already completed bays to harden. Then the edge boards are removed and the empty bays are cast, using the completed ones as a guide. Once you start casting a bay, it must be completed. Never interrupt a concreting process, as this can result in a faulty bond and the joint will always be visible.

A quick guide to the sequence of operations for casting a floor see Figs. 1 to 8 below.

Fig. 1. Clean the area, clean the edges of the footings. Level the area with a shovel.

Fig. 2. Mark the bays on the walls. Set out the positions of the edge boards on the ground.

Fig. 3. Fix the edge boards with pegs. Level the tops of the edge boards. The corners should match ( A to A )

Fig. 4. Pour guide strips to the height of the baselayer. Level the guide strips.

Fig. 5. Pour the base layer and tamp it down with the rammer to the required level.

Fig. 6. Lay the floor screed layer ( fairly dry mix ) and tamp it down with the wood float until moisture comes through.

Fig. 7. Finish off the top with the trowel or steel float. Make a bevel along the edges for the shrinkage joints (arrow).

Fig. 8 Take away the edge boards and put sand on top of the floor. Water the floor regularly.

SHRINKAGE GAPS

When one set of bays has hardened, the edge boards are carefully removed and the remaining bays can be cast. Shrinkage gaps are made between the adjoining bays. This is done by placing plastic or paper between the bays when the second set of bays is cast, so that the bays are kept separate from each other.

The shrinkage gaps allow the concrete bays to shrink a bit as they harden without cracking. This type of gap is used where the floor is not exposed to the sun or to great temperature changes; usually only for inside floors. Shrinkage gaps cau be made in either one-course work or two-course work. A "V" is made along the top edges of the gap to improve the appearance of the floor (Fig, 1).

EXPANSION GAPS

Where the floor is exposed to the sun, as in a verandah floor or any concreted area outside the house Itself, expansion gaps have to be made. in this case the edge boards are not removed until all the bays have been cast and hardened. The boards are then removed and the gap between the bays is filled with wet sand, and the floor screed is applied over the top (Fig. 2). Expansion gaps can only be made in two-course work.

The expansion gap allows the floor to expand and contract with the temperature changes without forming cracks. Expansion occurs when the floor is heated by the sun during the day, and shrinkage occurs at night when It cools down. Floors exposed to the sun should be divided into bays of no more than 5 square metres, and expansion gaps should be made in them. The floor screed must also be provided with a shrinkage gap; this should be located directly above the expansion gap in the base layer (Fig. 2).

SEQUENCE OF OPERATIONS FOR ONE-COURSE WORK

The hardcore filling is usually made well beforehand, to allow it to settle properly. It is constructed as explained on the Hardcore Filling page. The last 6 cm up to the top of the footings is filled with sand. The hardcore forms a firm support for the floor (Fig. 3).

a. Clean the vhole area and level the sand surface (Fig. 1).

b. Divide the area of the room into bays and mark the bays on the walls (Fig. 2).

c. Mark the positions of the edge boards on the sand between the marks on the walls (Fig. 2). Lines may also be fixed between the wall marks at the height of the finished floor level (Fig. 3).

d. Cut the edgeboards to the proper length. Note the arrangement of the boards shown in Fig. 4 and Fig. 6 below, and cut the boards so that they fit in this pattern.

e. Nail the pegs to the sides of the edge boards.

f. Place the edge boards as shown in Fig. 4, along the marks. The corners of the boards should meet as shown in Fig. 6 below.

g. Knock lightly on the pegs until the edge boards are level (check with the spirit level) and at the correct height (che tops of the boards should be level with the finished floor surface).

h. Pour the guide strips to the height of the base layer (approximately 8 cm) (Fig. 5). Level the tops of the guide strips (Fig. 7).

i. Pour the concrete for the base layer of one bay, making sure that it is well distributed near the walls and corners especially. (Fig. 1 below). Mix proportions can be found in the Concrete page.

j. Compact the concrete with a rammer, especially the corners and edges.

k. Use the notched strike board (Fig. 3) to level the surface by gently tamping until the layer is screed-thickness below the top of the edge boards.

1. Prepare the mortar for the screed layer. This should be moist but not wet.

m. Pour this mortar on top of the concrete. The screed is about 2 cm thick.

n. Tamp the screed down with a strike board until a level surface is obtained (Fig. 2).

o. Use the wood float to tamp the screed until the moisture from the concrete comes through. At the same time smooth the surface with the float. During this operation dip the float regularly in water and sprinkle water on top of the screed if necessary to make the work easier.

p. If a smoother surface is desired, finish off with a steel float. Make a chamfei along each edge next to the edge board to form half of the "V" groove above the shrinkage gap (Figs. 4 & 6).

q. If blisters or bubbles appear when the concrete starts to harden, pop them and close the holes.

r. Let the floor harden for some hours, then sprinkle water over it. Keep the floor wet at all times.

s. The next day, put some clear sand on top of the floor and wet it thoroughly. Keep the sand wet until the hardening process is over in several days time.

t. Remove the edge boards and cast the remaining bays in the same way. Make sure that the bays are separate by putting pieces of plastic or paper between them before pouring the concrete in the other bays (Fig. 5). The tops of the finished bays act as guides for the strike boards, but be careful not to damage them (Fig. 7).

VERANDAH FLOORS

The construction of a verandah floor is different from that of an inside floor in three particular ways.

Usually the verandah floor is built with a small slope towards the outside so that rain water can run off quickly (Fig. 1, a).

The verandah floor can have a projecting outside edge (Fig. 1, b).

Because the floor is exposed to the sun, expansion gaps have to be made in it. This means that the floor must be made with the two-course method.

SLOPING FLOOR:

Verandah floors may have a slope which is about 1%; no more than 2%, because this could cause problems in walking and working on it. The greater slope increases the danger of slipping when the surface is wet.

A slope of 1% means that the floor slopes 1 cm lower in every metre; in this case the slope is across the width of the floor.

The construction of the slope is done by simply setting the edge boards between the bays at the required slope.

PROJECTING OUTSIDE EDGE:

If the outside edge of a verandah floor is kept flush with the render of the footing (Fig. 2), then cracks would soon appear along the edge. This is prevented by constructing the floor so it projects past the footing by no more than 7,5 cm. The shorter the projection the better, because the floor is not reinforced.

FLOOR CONSTRUCTION.