1How strong is the block?

The strength of the finished block is determined by the mixture. The recommended mix is 2,5 level wheelbarrows of sand, 1 x 50kg bag of 42 MPa cement and 2,5 level wheelbarrows of chipped stone (Not larger than 13mm stone), gives a block of roughly 5,2 MPa strength. The required strength in most countries for a concrete block (Reference B-Block) is 3,5 MPa. The block can be strengthened to any level by simply adding more cement. The above mixture makes 32 large blocks.

2Can other fillings be used?

The blocks can be made with any material that can bond with cement. As stated previous, the strength of the finished block will depend on the material used. For example, volcanic sand/any crushed rock material is ideal when mixed with cement. Please note: ORGANIC material is not suitable for making the blocks and should not be used.

3Can any sort of sand be used?

Yes, any sort of concrete or plaster sand may be used but the finer the sand the weaker the finished block will be. Sand containing any organic material or salt should not be used. River sand is preferred. Sand with best properties comprise of particulars that has a variation of fine to coarse sand grains and must have no clay form.

4How does Stumbelbloc save cost in building?

Much less material is used than in conventional building and the labour cost is a fraction of the normal rate because unskilled labour can be used to do the work of otherwise expensive artisans. For standard openings (windows/doors) Stumbelbloc may be used in place of lintels – saving time, money and procurement/delivery costs. Finally, the use of Stumbelbloc eliminates almost all building waste. Any surplus standard mortar can be used to make more blocks.

5How does it save time?

The method of building is 10 times faster than normal. A standard structure can be built to roof height in one day. No time is wasted on setting up profiles and preparing mortar mixes. The labourer carrying the block actually lays it instead of handing it to the artisan. No time is spent cleaning up afterwards. If required, several labourers can work at the same time without interrupting each other’s work.

6Are there other benefits?

Apart from being able to use people who have never constructed a dwelling before, the speed of the process allows very productive and profitable results. From a social perspective, Stumbelbloc allow unskilled workers – even if they are unable to read or write – to both make and build with the blocks without any energy or power source. Some simple tuition is all that’s required. Blocks can be made in remote areas (Including disaster zones) providing that local sand and cement is available. The resulting structures providing permanent and very robust accommodation.

7What are its thermal properties?

Because the block is wet cast, it is far more dense and compact than dry pressed block and is therefore superior in thermal and strength quality. The construction method using the bed mortar leaves the block cavities completely clean. Traditional blocks need standard mortar which tends to block the cavities. Of course, the cavities themselves may be filled with any form of insulation material.

8How will the plumbing and electrical installations work?

These are all simply fitted into the hollow cavities which are completely clean by virtue of the bonding process.

9How high can you build in single level?

This is determined by the block strength. 4, 8 MPa can build up to 5, 3 m load bearing walls. Maximum wall plate height is 3, 5 m and maximum gable height 5, 3 m

10How many levels can you build?

Stumbelbloc has been approved in South Africa for single storey dwellings only. Refer to your countries building regulations and requirements of MPa strength for different levels

11How many moulds do you need to make enough blocks for a house?

This depends on how much time you have and the size of the house. A small dwelling of 58 m² needs 1 500 blocks. 60 moulds will keep 1 labourer busy daily and will produce the required number of blocks in 50 days. 2 labourers will mean 25 days etc. And so on prorate.

12How much does it cost to build a structure?

Obviously, this will depend on the type and size of structure and, the local material and labour costs.

13Can you build a swimming pool, pond or anything else with it?

Anything that is ordinarily built with traditional blocks can be built with Stumbelbloc , but with Stumbelbloc it is cheaper, faster and easier.

14What approvals does it have?

Made to the recommended concrete mix at 4, 8 MPa Stumbelbloc blocks conform to SABS requirements of more than 3, 5 MPa. When built with SABS and NHBRC approved thin bed mortar, they can legally be used to build with in RSA. Stumbelbloc does have Agrement and NHBRC approval.

15Do the structures need to be rendered or bagged?

Ideally, yes. In order to maintain structural integrity, it is recommended that a suitable plaster is used. This not only provides a cost effective and waterproof layer to the blocks, but also penetrates the horizontal gaps between them.

For thin bed mortar “Block Grip™” and “Skim Plaster™” please visit www.technicalfinishes.com