Introduction to concrete building products
Practical Action
Figure 3: A building of concrete blocks and roof tiles in Nepal. Photo: Practical Action.
Concrete blocks are usually popular with builders and building owners. Building with them is not
particularly heavy work, unlike the construction of rammed earth walls, and the builder does not
have to have specialist bricklaying skills. The owner may like the thickness of the block walls
which confer security and provide good insulation, and may consider a concrete block house to
confer a degree of status within the community. As a result the producer may not find it too
difficult to sell blocks to small-scale builders and plot owners, provided the selling price is not
considerably more than that of other materials.
Drawbacks of Concrete Products
Up to now this guide has considered mainly the benefits and advantages of concrete products, but
there are also some disadvantages which need to be mentioned.
Firstly cement is used in making the blocks, and in many countries cement is a very expensive
commodity. The producer who can minimise the usage of cement through good quality control is
at an obvious advantage.
Also, because cement hardens and gains strength rather slowly, concrete products require one or
two days undisturbed curing before they can be handled and then at least a further seven days of
curing before they can be used in building, a large curing area is required where a whole days
production can be set out. In the middle of a city, where land prices can be high, concrete
products manufacture might not be feasible.
In addition, although blocks, which are usually made with a semi-dry mix, can be turned out of
their moulds straight after casting, other products are usually made with a wetter mix and so need
to be left in the mould until hardened. The producer therefore needs to invest in a large number of
moulds - equivalent to a full day's production. Steel or plastic moulds are expensive and buying a
large supply of them would form a sizeable part of the investment in the whole plant.
When concrete blocks are taken out from the mould, they have little strength and are very fragile.
Handling them carelessly at this stage can result in a significant number of damaged and worthless
blocks.
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