Mixing And Using Cement

One of the most common materials used in home and garden is cement. There are two main types of cement mixture mortar and concrete.

In mortar, cement is mixed only with sand. It is used for building in bricks or concrete blocks and also for the final surfacing of floors and some outdoor walls. Concrete, besides sand and cement, includes varying proportions of gravel. This both reduces the cost of a given volume of mixture but also, to some extent, helps to prevent cracking.

In mixing either mortar or concrete one uses different proportions of sand, cement and gravel for various purposes. Speaking generally, the higher the proportion of cement, the strong the result will be. However, no matter what the proportions may be these are always given by volume, not by weight. A common mixture for mortar is, for example, one part of cement to three parts of sand.

This means that you should take one level bucket of cement and add to it three level buckets of sand.

All materials are mixed together dry, until they reach a perfectly even colour. This is best done by working on a large flat surface. Heap the sand, cement and gravel together and then shovel the pile bodily to one side. After this, return the heap to its original position. Four or five turns like this will ensure that all the particles are intimately mixed. Next add the water. Unfortunately, it is not possible to specify exactly how much water will be needed for any particular amount of cement. This is because the s.:nd and gravel will themselves contain some water. What is important though, is to make sure that you use rather too little water than too much. It is a common amateur mistake to make concrete much too wet, which results in a weak mix that cracks and powders badly.

Adding water is done differently with mortar and with concrete. A mortar mix should have a hole opened out in the top, ratar like the crater of a volcano. Into this pour water, into which you can then gently work the dry powder from the edges. Add more water gradually until the whole heap is evenly moist.

With concrete, the whole heap is sprinkled with water from a fine rosed hose or watering can. Then the dampened mixture is turned underneath and more water sprinkled on. If large amounts of water are flooded on to a concrete mix, it will tend to wash the gravel clear of sand and cement, resulting in an uneven mixture.

Mixing cement of any kind is a heavy job, especially if you attempt too much at one time. If you have much to do it pays to hire a small power driven cement mixer. These can be obtained in most large towns. The dry materials are put in the container and this is run until they reach an even colouring. Then water is added till the mixture is suitably wet.

Coloured mortars or concretes can be made by adding dyes to the dry materials, following the manufacturer’s instructions. Waterproof concrete for ponds is produced usually by adding a waterproofing chemical. Building mortar may be made easier to work by adding a plasticiser, a chemical which can be bought at builders merchants. Often, for this purpose lime is used as well as cement, both for economy and to make the mixture more workable. Where speed of drying is essential, you can also buy rapid-setting cement or separate chemicals that can be added to ordinary cement. There are also frost-proofing chemicals which will prevent the damage that usually occurs to newly-placed concrete if this is exposed to frost before it is completely set.

Storage—Only buy enough cement as is necessary for the job in hand, for it is almost impossible to store it for long at home. It becomes damp and hardened. It then loses much of its strength and should only be used in places where this is unimportant.

You can purchase ready-mixed dry materials for mortar from many chain stores. This makes excellent mortar when mixed with water but is an expensive way to buy if you need more than a few pounds.

For really big jobs, such as paths or drives, or large concrete floors, ready-mixed concrete can be bought. This is delivered in specially equipped lorries and, provided there is access for these big vehicles, the drivers can often place the concrete roughly in position for you. Since the minimum order is usually about 2 cubic yards, weighing several tons, and since all the concrete must be placed within a few hours, it is essential to have the placement area ready and plenty of willing helpers, wheelbarrows, shovels and strong rakes available.

In some areas, it is even possible for such ready-mixed concrete to come to less than buying small quantities of dry materials and hiring a mixer to do the work yourself.

Useful mixtures for mortar and concrete Mortars

For building generally with bricks and blocks.

  • ONE part cement.
  • One part hydrated hydraulic lime.
  • SIX parts builders sand.

For stronger work, floor surfacing and embedding slabs outdoors.

  • ONE part cement.
  • THREE parts sand.

Concretes

Outdoor, large paths and drives, floors, etc. needing great strength.

  • ONE part cement.
  • TWO AND A HALF parts sand.
  • FOUR parts coarse gravel.

Light garden paths, thin slabs, etc.

  • ONE part cement.
  • TWO parts sand.
  • THREE parts coarse gravel.

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