Questions we are asked about concrete
Most concrete problems in Nairobi are decided before the truck arrives: the class, the volume and the access. These are the questions worth asking before anyone quotes. See also ready-mix prices, cement prices and what the grades mean.
- What does ready-mix concrete cost in Kenya?
- Delivered in Nairobi: roughly KES 9,500 to 10,500 per m³ for Class 15, 11,500 to 13,000 for Class 20, 13,500 to 16,000 for Class 25 and 15,200 to 19,000 for Class 30. Pumping is added from about 700 per m³ on top. Placed rates, which include labour and formwork, are a different and higher number.
- Why do supply and placed rates differ so much at Class 30?
- Because the gap is labour, formwork and compaction, and it widens with cement content. Supply-only Class 30 sits around 15,200 per m³ while published contractor rates for placed Class 30 reach about 19,200. Comparing one against the other in either direction will mislead you by roughly a quarter.
- Which cement grade do I need?
- For structural concrete, 42.5: Bamburi Nguvu, Bamburi Powermax or Simba 42.5N. The 32.5 cements, including Bamburi Fundi and Tembo, are masonry cements for mortar, plaster and screed. Using 32.5 in a slab saves about 75 shillings a bag and permanently reduces what the structure carries.
- What does C25 actually mean?
- Twenty-five megapascals of characteristic compressive strength at twenty-eight days, on standard test cubes. It is a performance specification rather than a recipe, which is why batching to a class is more meaningful than mixing to a nominal ratio like 1:2:4.
- Why is adding water at the chute such a problem?
- Strength is governed principally by the water-to-cement ratio, so extra water makes concrete easier to place and weaker in roughly equal measure. It is the single most common way good concrete becomes poor concrete on a Kenyan site. If a mix is too stiff, the answer is a plasticiser or a slump specified at the plant.
- Is there a minimum load, and what happens below it?
- Yes, and below it you are charged for the drum rather than the concrete. On a two or three metre pour that surcharge can approach the value of the material, which is why a volumetric truck that mixes on site is usually the cheaper answer for small work. We will say so rather than sell you a part load.
- How do I compare aggregate quotes?
- Insist on a rate per tonne and the payload of the vehicle. Kenyan aggregate is quoted per lorry and a seven-tonne Isuzu and a twenty-two-tonne trailer are both a lorry. Published ballast figures that appear to span a factor of three all sit between about 1,350 and 1,850 per tonne once you divide.
- Do I need a pump?
- If the pour is above ground floor, yes. If a loaded truck cannot get within reach of it, also yes, and in Nairobi that second reason is the more common one. Decide when you book, because a pump is a scheduled resource and asking for one on the morning means concrete waiting in a drum.
- How much notice do you need?
- A few days for a standard delivery. Longer where a pump is involved, where an estate needs to clear a heavy vehicle, as in Runda, or where the site can only take deliveries at night, as on Westlands commercial sites. Those are permissions and scheduled equipment rather than things available on request.
- What happens if I order too little concrete?
- You get a cold joint, which is a plane of weakness through the element and cannot be repaired once the formwork comes off. It is why we calculate from drawings and add a realistic allowance: a small overage costs a few thousand shillings, and the alternative cannot be bought back at any price.
- Can you deliver in the long rains?
- To the site, yes. Onto the plot, it depends on the plot, and that is a real question in Syokimau, on unfinished Kiambu Road estate roads and on the private approaches in Karen and Runda. Where unsurfaced access will not carry thirty tonnes, we discharge on made ground and pump the rest.
- Do I get proof of what was delivered?
- A batch ticket with every load, showing the class. On anything structural that ticket is the only evidence you will ever have that what you specified is what went into the building, and it is worth keeping with the project records rather than losing on site.
- Where do you deliver?
- Across Nairobi and the surrounding construction corridors: Karen, Kilimani, Kileleshwa, Lavington, Westlands, Runda, the Kiambu Road and Thika Road corridors, Syokimau, Athi River, Ruiru and Kitengela. Each area page sets out what is genuinely different about delivering there. Open Monday to Saturday, 6am to 6pm.
Send us the area
The class, the cubic metres, the date and a photo of your gate. We will come back with a rate and a slot, and tell you plainly if the truck cannot reach the pour.
Sub-base compacted in layers · edge restraint haunched · falls set at survey, not by eye