Concrete is made from natural materials, and this means the surface has character as it is naturally variable - one of its key design benefits. From experience we know that the inherent natural properties of concrete are not to everybody's taste and it is important you understand the following.
Concrete is a porous material with a smooth or rough surface that can become the victim of stains, dirt, biological growth, etc. The situation in which the concrete is being used and its surrounding environment will significantly influence the concrete colour - exactly the same as for paint. The amount and type of light reflected on the coloured concrete changes the appearance, as will surrounding decor and furnishings.
How concrete is finished, trowel strokes (will be visible) in different directions, concrete finished in the shade versus being finished in the sun, using a steel trowel or a mag float on different angles or in different ways will all significantly contribute to the finished surface. It is important to understand that once acid has been applied to concrete in different application methods it may darken the concrete surface and may expose some aggregate. It is very important to choose the right contractor for this.
When sealer is applied to concrete it changes its appearance, again similar to what you see on a sample disc (shading). Sealing will also significantly change the slip resistance whether the surface is steel trowel finish, broom finish or exposed pebble/aggregate.
During the first two weeks of curing the concrete may also become slippery as all the calcium and salts are brought to the surface, this will wear off over time. All these noted in this information sheet should be considered when choosing a concrete type and finish along with the concretes use and being fit for a specific purpose.
The colour of normal concrete, even without added colour pigment, varies with a number of factors like raw material color, weather conditions on the day, how it is handled and placed, and how it cures and dries. The colour made is absolutely consistent but when it is added to concrete the same normal variations can occur as above - the tone is the same but the shade may vary. Plus, all samples are cast in a mould under controlled conditions so the texture and colour will not represent the surface on site.
Cracking can happen and should be expected in most cases. As concrete hardens, excess water evaporates which causes the concrete to shrink, and this is what can cause cracking. The proper use of construction cuts, proper site preparation, and good concrete placing and curing will significantly reduce the risk of any cracking. Even then, cracks can occur. To find out more information on cracking please visit the Cement and Concrete Association of New Zealand webpage.
Occasionally, after the concrete is sealed, dark patches may appear when the surface is wet and then disappear when the surface dries. This is called ‘measling’. It’s caused by microscopic holes / cracks / high-points in the sealer that let small amounts of water into the concrete. It only happens from time to time and is the result of concrete being concrete, not because of bad workmanship or faulty materials. The effect will occur less and less over time. To fix it, we suggest topically applying more coats of sealer. You need to be careful however, not to add too many coats over large areas as it may make the surface more slippery.
Very occasionally irregular, dark blotching (or “Pinto”) may appear on the surface of your concrete. This can happen regardless of whether colour is used or not. It’s not known exactly what causes this, but it seems to be related to the curing of the concrete i.e., how it dries and how moisture moves through the slab. Ensuring consistency of placing and curing across the slab should help to prevent it. If this does occur, sanding the surface then applying a light acid wash may reduce the effects.
Concrete has a characteristic mottliness or cloudiness. Peter Fell colours or other suppliers’ colours often highlight and extend this. It is unlikely to be uniform colour, but this is part of the appeal. It gives your space a natural element – one of the key design features of concrete.
Efflorescence is a crystalline deposit of salts, usually white, that forms on or near the surface of concrete. It forms when salts are dissolved by water migrating through the concrete then precipitated at the surface. Efflorescence is particularly noticeable on dark or coloured concrete where its effects are seen as colour differing in intensity and shade from that intended, varying over the surface and changing with time. Efflorescence cannot be removed by traditional cleaning products, can often be treated with a mild acid watch. In the Peter Fell System, PFL Surface Preparation, PFL Surface Prep Lite or PFL Acid Gel can be used to treat efflorescence and sealing the concrete can prevent any reoccurrence of the salt deposits.
If you are planning on using coloured concrete in your next project there are a few important things to think about. Put time into thinking about the layout and design of the area.
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