AMOUNT OF CEMENT USED IN AN AVERAGE 3 BEDROOMED HOUSE IN KENYA.
Cement cost takes an average of 35% of the total cost of construction of an average house basing on a low cost finish overall estimate of KES 20,000per m2. This is approximately KES 7,000 per m2.
The amount of cement used in total for an average 3 bedroomed residential house of 100m2 in plinth area is 958 bags at a cost of KES 691,000 basing on a price of KES 720 per 50kg bag.
A square meter of building in Kenya will use 9.6 bags.
2 BEDROOMED FLAT.
The average 2 bedroomed house in a middle class area such as Ruaka, Rongai, Kitengela, Ruai is approximately 60m2 in plinth area. This translates to 60m2 x 9.6bags=546bags costing KES 414,000.
A block of 2 bedroomed flats in the middle class neighborhoods standing on a 1/8th acre can contain 20 units. This means the total cement used will be 20 units x 546bags per unit=10,920 bags costing 7,800,000 KES.
SHOPS AND SINGLE ROOMS 1Oft by 10ft.
The average 10ft by 10ft room used as a shop or single room residence is approximately 10m2 in plinth area. This translates to 10m2 x 9.6bags=96bags of cement costing KES 69,100.
The breakdown is as below.
Foundation.
| weight tonnes | cement bags | cement price | ||||
| cement | sand | ballast | ||||
| Blinding1.4.8 |
0.461538 |
1.969231 |
3.938462 |
9.230769 |
6646.154 |
|
| Footing1.2.4 |
3.214286 |
6.857143 |
13.71429 |
64.28571 |
46285.71 |
|
| Floor1.3.6 |
5.4 |
17.28 |
34.56 |
108 |
77760 |
|
|
181.5165 |
130691.9 |
|||||
WALLING. Ratio of 1.4
|
|||||||||||||||||||||||
BEAMS AND COLLUMNS. Ratio 1.2.4
| weight tonnes | cement bags | cement price | ||||
| beams | cement | sand | ballast | |||
|
5.571429 |
11.88571429 |
23.77143 |
111.4286bags |
80228.57 |
||
| collumns |
0.857143 |
1.828571429 |
3.657143 |
17.14286bags |
12342.86 |
|
FLOOR PLASTER. Ratio 1.3
| weight tonnes | cement bags | cement price | |||
| cement | sand | ballast | |||
|
1.875 |
6 |
0 |
37.5bags |
27000 |
|
WALL PLASTER. Ratio 1.4
| weight tonnes | cement bags | cement price | |||
| cement | sand | ballast | |||
|
5.97 |
25.472 |
0 |
119.4bags |
85968 |
|
EXTERNAL KEYING. Ratio 1.4
| weight tonnes | cement bags | cement price | |||
| cement | sand | ballast | |||
|
0.672 |
2.8672 |
0 |
13.44bags |
9676.8 |
|
ACTUAL SITUATION ON THE GROUND.
In most small scale residential projects, the house owners usually rely on the local Fundi expertise on the mix ratio of cement. The usual tools used to measure the volumes are spades, wheel barrows and 20 liter water buckets.
8 wheelbarrow of sand/ballast make 1 tonne.
Four wheelbarrows are used to mix 1 bag of cement to 8 bags of ballast.
I bag of cement has 0.035 cubic meters in volume.
1 wheelbarrow has the below volume.
Assuming sand has a density of 1600kg/m3 and 8 wheelbarrows make 1 tone, 1 wheelbarrow has 1000/8=125kg.
1 wheelbarrow of sand has 0.08 Cubic meters in volume.
This sand volume per wheel barrow when compared to cement volume per bag gives a ratio of 1 cement volume to 2 sand volumes.
LOCAL FUNDI MIX.
The usual mix used by local fundis of 1 bag cement to 4 bags sand is actually 1 cubic meter cement to 8 cubic meters sand to 16 cubic meters ballast.
A ratio of 2 bags cement to 4 wheelbarrows sand to 8 wheelbarrows ballast is 1 to 4 to 8 which is still low for concrete works such as foundation footings and beams which require a ratio of 1 to 2 to 4 or 1 to 3 to 6.
This type of mix works well for single storey residential houses.
BUILDING COLLAPSE.
In the event that the ratio of 1 bag cement to 4 wheelbarrows sand to 8 wheelbarrows ballast is used for a building that is several storeys high, serious risk of collapse is imminent due to a very weak cement ratio. This could be the reason for the various building collapse being witnessed in Kenya and recently in Tanzania and India.
Francis Gichuhi Kamau, Architect.
info@a4architect.com
0721410684.
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