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Polished Concrete

Polished concrete is a popular choice for hard surfaces that might otherwise be tiled. It can be plain concrete (in fact many existing floors can be polished with great results) or it might be concrete made with specially selected aggregates and oxides. Floors can be heated with electricity or water heating methods. Alternatively floors can be heated with passive solar gain taking advantage of concrete's high thermal mass (basically because concrete is a very dense material, good design can allow for concrete to be cool in summer and warm in winter.

Some polished concrete benefits are:

 

Concretes high mass provides great thermal properties, concrete floors wont

dramatically change temperature unlike tiles. Passive solar design incorporating

concrete floors can provide very comfortable homes.

 

Polished concrete reflects light, reducing costs in commercial areas, and improves

natural lighting.

 

Polished concrete floors don’t retain dust or dust mites (great for asthmatics)

 

Polished concrete is affordable, most homes already have a concrete floor specified.

Even standard concrete floors look great polished.

 

Polished concrete can be unique, you chose the depth of the grind, the oxide and

the aggregates (such as limestone, river pebbles etc..)

 

About the process

Talk to your builder, your builder must be “onboard” with the polished floor

concept. Great care should be taken to plan for good crack control, well placed saw

cuts or possibly crack inducers at key locations to reduce drying shrinkage stress in the polished floor areas. This planning must be done prior to pouring concrete. A simple thing such as fixing wall brace props in the middle of a polished floor might ruin the appearance. We will gladly meet you and your builder on site and discuss all aspects.

A 25MPa minimum grade concrete needs to be used with your choice of aggregates and oxide. Always notify your concrete supplier that you intend to polish your concrete floor.

The concrete placer and all contractors working with the floor must be aware that the floor will be polished (ie the concrete placer will be careful to place the concrete in a manner to maintain an even distribution of aggregates (as best they can).

Once placed the concrete should be cured (ideally with water for at least 7 days).

After approx. 14 days the floor can get the initial grind (preferably before frames are erected). We suggest asking for samples of various depth (2-5mm) grinding be made in a discrete area for your approval.

We suggest the concrete be covered and protected from staining (ie. builders hammers & coffee!) with polythene or your grinding contractor may put a temporary sealer over the concrete. Plywood or carpet may stain your concrete so be careful!

When construction is almost complete your grinding contractor can either:

a. “Grind and seal” where the concrete is ground (any voids or defects are filled with a slurry coat) and sealed with a urethane, epoxy or similar.

b. “Grind and Polish” where the concrete is ground (any voids or defects are filled with a slurry coat) and a surface densifier (typically sodium or lithium based) is applied and the floor is polished.

 

 

Important points

Your concrete contractor will use his experience to place the concrete in such a way as to provide a uniform appearance when the concrete is polished (usually the concrete is placed similar to an exposed aggregate). There will naturally always be some variations in finish.

Although concrete aggregates are washed and are generally very clean due to the sources of these materials they main contain impurities such as small pieces of wood, iron or coal, these may be visible in the final product.

What can go wrong?

Actually, lots can go wrong. Polished concrete floors are easily obtainable but the customer must accept the chance of things not going to plan. For example;

 

It could rain on the concrete during placement.

 

The floor could crack after all precautions have been taken.

 

The weather conditions could cause problems with the concrete finishing process

 

It is possible that contaminates such as driftwood, coal, blasting cord, polystyrene or other impurities are noticeable in the finished floor.

 

Machinery breakdowns (concrete plant, concrete truck, concrete pump, finishing equipment.)

 

There will always be minor defects, remember it’s the overall appearance of the floors that’s important. If these risks are unacceptable a factory made flooring solution such as tiles, vinyl, carpet or timber will be a safer choice but they will never have the character of polished concrete!

 

We suggest you discuss all options with your grinding contractor before placing concrete.

 

Always remember

As with any concrete project the same basic principals apply which are; well compacted base course, well positioned reinforcement, sensible concrete thickness (we recommend 100mm min. for residential works), consistent water curing as soon as possible, well positioned joints (tooled joints may be required at high risk areas), saw cutting as soon as is practical.

 

 

 

 

Counties Ready Mix Ltd | Phone: 09 2946222 | Fax: 09 2946333 | email: info@crml.co.nz | PO Box 471, Drury, 2247

Physical address: 14 Bremner Road, Drury, Auckland, New Zealand | Google map link