Sandcrete Blocks
The term sandcrete comes from "concrete" by replacing the first syllable "con" with the word "sand". This is done to make it clear that this building product contains only sand as an aggregate, and no stones. It can also be called "fina-grained concrete" but the new term sandcrete is preferred as it corresponds to landcrete.
A pallet is put into the mould box of the machine and the box is filled with a mixture of cement and sand; then the lid of the machine is used to compact the material to the required size (for proportions of the mix, see the Table).
Unlike landcrete blocks, sandcrete blocks have to be made upon a pallet, as they are too soft to be carried when freshly made. Differently shaped blocks can be made with this machine by changing the height of the pallet or by using inserts.
MAKING THE BLOCKS
Making blocks with this machine is similar to making landcrete blocks.
a. Put one or more pallets into the mould box, according to how thick you want the blocks.
b. Half-fill the mould box with the ready mixed sandcrete.
c. Compact the corners with a piece of wood.
d. Fill the mould box completely and again compact the corners. Add a little more if necessary to fill the box flush to the top edge.
e. Compact the sandcrete by repeatedly banging the heavy lid on it, until the lid fits exactly in its lowest position. Sometimes the lid does not close properly because the mould box is too full. in this case, scrape off a small amount of sandcrete with your trowel and repeat the compaction. If you fail to do this the block will be wedge-shaped and difficult to set in the wall.
f. Open the lid wide and pull the handle to push the block out.
g. Remove both pallet and block at the same time and set them in place for hardening and curing.
- NOTE: Before use, the pallets must be soaked in water thoroughly, to prevent them from bending during the drying process. If this is not done the pallets will probably bend and crack the blocks.
DECORATIVE BLOCKS.
PLANNING THE WORK
As in the plan of operations for making landcrete blocks, for sandcrete blocks also the speed and ease of the work depend on how well it is planned.
Fig. 1
Originally, a decorative block was understood to be a solid block with decorative textured faces. What we now commonly call decorative block is in fact part of a decorative openwork screen built intc an opening. The correct term is "decorative grille" (also spelled "grill"). This kind of block is made in a special iron mould. It can serve several purposes:
- To give an attractive appearance
- To provide light without installing burglar-proofing or any kind of louvres, shutters, etc.
- To provide permanent ventilation without using ventilation blocks
- Or a combination of two or three of the above requirements.
The illustrations of blocks on the opposite page show that almost any design is possible, given a fertile imagination. Remember however that the strength of the blocks depends also on their shape (Figs. 1 to 5).
NOTE: To make it easier to empty the mould, short pins can be welded onto each corner at the top of the mould. This allows you to tap the pins gently on a hard, level surface; thus loosening the block from the mould (Fig. 6).
Drilling small holes into the bottom of the mould can also make it easier to remove the block. The holes allow air into the mould as the block comes out.
VENTILATING BLOCKS
These are blocks which have an opening (or several openings) in them. They are used to ventilate rooms, stores, the spaces above ceilings etc.
There are various types of ventilating blocks. Some are designed to keep out rain, others include mosquito-proofing or a decorative front face (Figs. 1, 2 & 3),
In cases where a maximum amount of ventilation is desired, it is advisable to make a ventilating unit which is constructed out of two identical halves (Fig, 4). The inside of this unit can be painted in a bright colour, to increase the amount of light inside the room.
Simply shaped blocks for ventilation can be made in the sandcrete block machine by inserting wooden blocks according to the desired shape.
More complicated designs usually require a specially made wooden mould. The advantage of this kind of mould is that any size and shape of block can be made.
Pre-cast sandcrete or concrete are not the only choices of materials for ventilating units. Local potters' skills in baking earthenware can be used and one can design ventilating units from clay. Existing clay shapes can be used, such as tiles and pots (Figs. 5 & 6) or new shapes can be invented (Fig. 7).
When designing these ventilating units keep in mind Ihe direction of the driving rain. Make sure that the inside of the unit is higher than the outside, and that there is no place for water to become trapped inside the unit to make a breeding place for mosquitos (Fig. 5).
Apart from the above considerations, there is no limit to the imagination of the Rural Builder in designing different shapes and kinds of ventilating units.
