The interlocking Stumbelboc system is ideal for smaller builders.
The Cape Town Building Centre in Rondebosch is featuring a stand promoting a new concrete block-making system that can make building a lot simpler, says Mike Grose, chief executive of Technical Finishes which supplies the bonding agent for the blocks.
The system, to which the inventor and developer Andre Esterhuizen has given the name Stumbelbloc, will enable people in outlying areas to build for themselves at greatly reduced costs. The product is especially suitable for those in small rural communities, squatter camps, on farms or any area to which the delivery of concrete blocks might be prohibitively expensive.
Stumbelbloc supplies the customer with very strong plastic moulds into which the freshly mixed concrete for the blocks is then poured and compacted. The mould is stripped after 48 hours and the block is left to cure for seven days. The operation can be carried out almost anywhere, provided that there is water, cement, sand and stone available and provided that the curing can take place in the shade.
The moulds sell at R198 each with discounts for large orders.
The defining features of the new blocks, says Esterhuizen, are, first, that they are hollow core and therefore ideal for home building as they reduce heat transmission. Second, they have seven male/female indentations top and bottom which ensure that they interlock vertically with complete uniformity and do not require special blocks to go around corners.
“The ability to lock the blocks together imparts considerable extra strength to the wall structure and this is enhanced by the base of the blocks being dipped in a Technical Finishes product known as Blockgrip. This is a quick hardening cementitious product that sets in three hours and strengthens the joints between the blocks,” says Esterhuizen.
“The system does away with the need for conventional cement mortar (dagga) bonding and as a result makes for far faster building. Once the base course has been accurately laid, the blocks can be laid by unskilled workers after minimal training. What is more, they can start anywhere on the wall – two or three can work on the same course simultaneously because the blocks will always fit together.”
Esterhuizen says it is almost impossible to lay these blocks incorrectly. If a block is not laid as designed it simply will not fit. In this respect the system is similar to children’s building blocks, like Lego.
Two types of block are made: the full size block measures 398 mm x 178 mm x 198 mm. The half block is to ensure stretcher bonding as in conventional brickwork.
Esterhuizen stresses that, as the blocks are all handmade and as they do not call for a big capital investment, they are ideal for use in remote areas where job creation needs boosting and deliveries are expensive. They are also ideal for situations where the builder wants to conform to ‘green’ requirements: the manufacturer requires no power, minimal transport and makes little mess.
All those who have observed the operation in use have been impressed by the speed at which blocks can be laid, says Jamie Heathcote-Marks, general manager of the Building Centre.
“In one case,” he says, “a 2,4m high column was erected in under three minutes. This is a fraction of the time that would be required for conventional building with mortar.”
The block making, too, says Heathcote-Marks, is speedy: one person can make as many as 50 blocks in a single day.
A demonstration room (with a tiled roof) has been built at Technical Finishes’ Epping factory to demonstrate the new system. On this a three man team with no previous experience of the work were able to erect 30m² of walling, including a door and a window, in four hours. This time could be halved with a little practice, says Esterhuizen.
“The blocks are load-bearing from the moment they are laid. Provided good materials are used in the concrete, strengths of 9 MPa can be achieved quite easily. A standard double storey home requires block strengths of 7 Mpa,” says Esterhuizen.
Grose says there will be many small housing and building teams, farmers, township entrepreneurs and many hundreds of home handymen who will welcome this opportunity to produce a well finished, accurate block themselves at low cost.
“The new block design is perfectly adapted to the smaller operator who wishes to use his own labour force and to keep his costs substantially below conventional building methods,” says Grose. “Now you can build your own boundary walls, columns, additions, garages or even houses using this revolutionary system.”
Call Andre Esterhuizen on 083 228 8036 or Mike Grose on 021 535 4455.