INTERLOCKING STABILIZED SOIL BLOCKS CONSTRUCTION COSTS SAVINGS IN KENYA.
Interlocking Stabilized soil blocks are walling blocks made from compressed soil. They are just as hard and as water-proof as stone. Stone is made when soil is compressed by forces of nature while the Interlocking Stabilized Soil blocks are made when the soil is artificially compressed.
Interlocking Stabilized soil blocks are artificially compressed using either a manual or diesel-operated pressing machine to a pressure of between 20 to 40 kg/cm2.
Quarry stone has a compressive strength of between 2 to 5 N/mm2 depending on the type of stone which varies from region to region.
Interlocking Stabilized soil blocks have a compressive strength of 2.5N/mm2.
This shows that they compare well to quarry stone in terms of strength.
Reinforced concrete has a much higher compressive strength that exceeds 15 to 20N/mm2 depending on the mix ratio of cement; sand; ballast.
STABILISED CEMENT BLOCK COST BREAKDOWN.
Assuming an average price of KES 750 for a 50kg bag of cement, and KES 350 to 400 for unskilled labour per day, the cost of producing 1 meter squared is as below:
CEMENT-KES 7 per brick
LABOUR to manufacture brick-KES 4 per brick
LABOUR to make wall-assuming 1 fundi and 1 assistant at a total of KES 1,100 per day with a minimum of 500 bricks per day.-KES 0.4 per brick.
TOTAL=KES 11.4 per brick.
1 M2 of walling will have an average of 33 bricks.
The total amount for 1 m2 of Stabilized soil walling will be KES 378 per m2.
The above estimate assumes that the soil is freely available at the site.
If the soil is bought, the cost will vary as below:
Assuming soil is bought and transported to the site at a cost of KES 500 per ton, this translates to 225 bricks per ton costing KES 0.3 per brick.
There will be an additional cost of KES 0.3 X 33 bricks per m2=KES 10 per m2.
This will total KES 388 per m2.
In Nairobi and its environs, since there are large construction projects requiring deep foundation excavations, soil can be delivered to the site for free since the large building owners are required to dump the soil in far away located approved council dumping sites hence more convenient for them to deliver to a nearby site.
NO NEED FOR JOINING MORTAR AND PLASTER
Stabilized soil blocks eliminate the need for joining cement mortar in between the blocks. It also eliminates the need for plaster. It’s however recommended to paint is externally using water-proof varnish to make it more water –resistant.
Specific sections can be painted using contrasting colors to create creative interior wall patterns.
MASONRY STONE COST BREAKDOWN
Machine-cut stone delivered around Nairobi costs between KES 60 to KES 70 per block.
In 1 m2 of wall, there are 13 stones. This totals to KES 60 x 13=KES 780 per m2.
The stones require cement mortar for joining. Each m2 requires approximately 1m2 of cement mortar at a cost of KES 200 per m2.
This adds the amount to KES 980M2.
Masonry walling requires plaster on the interior surface and key finishing on the exterior surface. This costs a further KKES 200 per m2, adding the cost to KES 1,180 per m2.
After plastering, masonry walling will need paint since the dull grey color of cement cannot be left bare compared to the reddish stabilized soil block color.
Paint costs a further KES 200 per m2, totaling the amount of masonry walling to KES 1,380 per m2.
COMPARISON OF PRICES.
Masonry walling costs 256% more than Interlocking Stabilized soil block walling.
In an average bungalow, the total walling costs compared to the total cost of construction is 15% .
The 256% difference in walling between use of masonry stone versus use of interlocking stabilized soil block happens only in the 15% of the total construction cost hence not being strongly felt.
For example, in the www.a4architect.com Diamond House design, the phase 1 [49m2] costs KES 853,000 to construct using masonry stone.
If the masonry stone is replaced with interlocking stabilized soil block, this 49m2 house will cost KES 796,000, representing a savings of KES 57,000.
To achieve maximum results in terms of cost savings in construction, a holistic approach whereby all elements of construction are taken into consideration, from foundation to walling, roofing, windows, finishes, external works.
This holistic approach to design has been researched and compiled as the www.a4architect.com Diamond House methodology.
Architect Francis Gichuhi Kamau