So what is Concrete ??

Decorative Gard Art

So what is this white or grey slurry called CONCRETE that we use to make these wonderful decorative garden planters or beautiful garden art statues and plaques?  

CONCRETE is made by mixing:

• Cement
• Water
• Coarse and Fine Aggregates

CEMENT

Cement powder, when mixed with water, forms a paste. The most common type is portland cement (type I or GP) which is all you need for any small to medium statue or planter. The other types are more expensive and can dry quicker or harder with less heat or no shrinkage. Premixed or Ready mix concrete is more expensive. Simply keep it cheap. Freshness of cement is key though as the minute you open the sealed bag it begins to absorb moisture from the air which will make the lumpy and useless when mixed and poured. Before buying check the bag and make sure it is soft and pliable with no damage to the bag. When not using the cement keep in a dry, well aired place.

WATER

Water is mixed with the cement powder to form a paste which holds the aggregates together like glue. Water should be cool, clean, and free from any dirt, unwanted chemicals or rubbish that may affect concrete. Too much or too little water with not allow the concrete to set properly so add slowly to get the mixture to get like a thick stew but soft and creamy.

AGGREGATE

Aggregates are of two basic types:
COARSE: crushed rock, gravel or screenings.
FINE: fine and coarse sands and crusher fines.Sand should be concreting sand and not brickies sand or plasterers sand.

Aggregates should be:
STRONG and HARD A stronger, harder aggregate will give a stronger final
concrete. Never use a crumble or flakey rock like sandstone.
DURABLE to stand up to wear and tear and weathering.
CHEMICALLY INACTIVE so the aggregates don’t react with the cement.
CLEAN Dirt or clay sticking to the aggregates will weaken the bond between paste and aggregates.
GRADED Aggregates should range in size so that they fit together well. Rounded aggregates give a more workable mix. Angular aggregates make concrete harder to place, work and compact, but can make concrete stronger.

Look for the next post on Admixtures and what they do……

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