A Guide to Polished Concrete Part Two
Jun 29, 2016


SELECTING THE MIX

Concrete floors are normally made from three basic ingredients, sand, cement and aggregate.

The ratio of these ingredients to each other affects the appearance, colour, strength characteristics of the floor.

Sand is the base, the finer background material. The aggregate is the larger material, crushed stone chippings. The cement binds the mix together and affects its strength, colour and tone.

Other ingredients can be added to this core mix to alter the characteristics further.

A standard concrete mix has a ratio of 5 to 1 to 5 of sand, cement and aggregate.

The choice of sand, in itself, will hugely affect the appearance.

Its colour, grade and consistency will affect the base or background of the mix

There is an huge choice of concrete types available. Some options are more expensive than others. The most economical choice is to use a standard concrete mix or a mix with up to 70% Eco-cement (which is much lighter in appearance). The standard mix supplied by each factory will vary depending on the aggregate and sand types used.

The choice of aggregate, its colour, variety and size again will hugely affect the appearance of the floor.

Coloured aggregate can be applied to the concrete mix. The % and types of aggregates and sand in the concrete mix can be altered to lighten, darken or bring colour to the concrete floor. These will be exposed by the grinding and polishing process later. This is generally a more expensive way of altering the concrete colour.

A less expensive method of altering the colour of the concrete is to add a pigment. These are available in a wide range, with the cost varying depending on the selected colour.

Another option available is the seeding of glass into the mix. Seeding is where glass is sprinkled evenly into the freshly poured concrete. The grinding and polishing process will reveal the glass pieces. Nails, bolts, computer chips, or any other objects can be seeded into the mix and then polished smooth.

CONCRETE POURING TIPS

The ideal depth of the concrete screed over under-floor heating pipes is between 75mm and 100mm.

Ideally, polypropylene fibres should be used in the concrete mix to prevent tiny shrinkage cracks on the surface of the concrete.

Frost can damage concrete when the water content freezes causing blistering and cracking to the top of the concrete as it freezes. As a general rule Concreting should not be commenced until a temperature of at least 2°C has been reached on a rising thermometer and should be stopped when the temperature reaches 4°C on a falling thermometer. Every care should be taken to protect fresh concrete from the effects of frost by covering with layers of dry straw or other approved means.

Pour the concrete as is delivered from the concrete plant. Make sure not to add extra water to the concrete in the truck as this will weaken it.

When pouring the concrete, it is essential that the levels are correct.

If the floor is to be ground and polished the concrete should not be tamped as this will push the aggregate down from the surface resulting in patches in the floor where the aggregate wont be seen.

Once the floor has been poured and leveled you should wait until it has sufficiently cured which allows the bleed water to evaporate from the concrete. If the bleed water is not allowed to evaporate completely the water is sealed in the concrete resulting in a weakened top layer of the concrete.

The next step is to pan float the concrete and power-float it to fill any air pockets on the surface with the fat from the pan floating.


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