Frequently Asked Questions
Some common questions we are asked.
Honing provides the most-durable and most-versatile polished finish. It involves grinding the concrete surface (with progressively finer abrasives) until the desired glossiness/lustre are achieved. Grinding (depending on the depth) may expose the aggregates used in the concrete.
While normal concrete mixes can be used, special aggregates are usually chosen to give a polished stone appearance.
Hard aggregates such as quartz and igneous rocks (eg granite) are preferred as they polish well and provide a surface with excellent wear characteristics. Aggregate colours, types (round or crushed), sizes, mineral-content, etc can all be selected and blended to produce a variety of finishes including polished granite-type (reconstituted stone) finishes.
The cost of special aggregates for large areas can be reduced by using them only in a topping or by seeding them into the surface. Because the latter process is difficult to control for smaller areas, it may be more economical and/or better to simply use the selected aggregate throughout the mix.
‘Terrazzo’ is the name traditionally used for honed concrete incorporating marble aggregate it is now often used to cover honed concrete containing other aggregates. Glass has sometimes been added to give a translucent appearance, but this is not generally recommended since undesirable reactions can occur between the silica in the glass and the alkalies in the concrete.
There are a number of ways of providing a coloured surface to the concrete slab, ranging from the addition of a pigment into the concrete mix or topping to the application of chemical stains and dyes/tints to the surface (typically used when patterns are to be provided).
The use of pigments is the most common method of colouring the full thickness of the concrete or topping layer. The amount of pigment required is expressed as a percentage of the cementitious material within the concrete and is typically in the range of 5 to 8% of the mass of cement in the concrete mix.
When used in conjunction with a honed finish that exposes the aggregates, a dosage of only 1 to 2% is usually adequate since the colour of the exposed aggregates dominates the final appearance.
Integral colour - Pigments
Pigments are available as either powders, granules which dissolve, or liquids. The ultra-fine particles of the pigments disperse as fine solids throughout the concrete matrix and are bound into the concrete in the same manner as the other aggregates.
Dyes and tints
Dyes and tints contain coloured particles in either a water or solvent solution and can produce colours that are not available with chemical stains, eg red and yellow.
Dyes have very fine coloured particles and will penetrate into the concrete while tints have larger particles, are opaque and remain on the surface of the concrete. Unlike chemical stains, dyes and tints do not react with the concrete.
This makes the results more predictable and less dependent on the consistency of the concrete or the weather conditions. Dyes and tints produce strong vibrant colours and along with other colouring options, extend the palette of colours possible to provide a vast range of colouring solutions for both large and small projects.
Dyes and tints are also used to correct the results from chemical staining by colouring areas where the stain did not provide the required colour, or areas where the stain created a colour that was darker than intended.
The UV resistance, and hence the ability to use the product externally needs to be established for each dye or tint.
Polished concrete surfaces are easy to maintain, with regular cleaning generally being all that is required. Depending on the application and contribution of the concrete surface to the risk of slipping when wet or contaminated by other substances, the common maintenance issues are cleaning, application of floor polishes and replacement of the surface sealer.
These areas are covered in detail in Slip Resistance below.
Floors need to be regularly cleaned to ensure that the intended slip resistance does not diminish with contamination or over time.
As most level polished concrete floors will have adequate slip resistance if clean and dry, the simplest maintenance procedure is to avoid contamination. If contamination does occurs, its spread over the remainder of the floor should be limited by prompt cleaning.(Mop and bucket, steam cleaning).
Slip resistance is a measure of the ability of a surface to substantially reduce or prevent the risk of a pedestrian slipping in both dry and wet conditions. With the increasing popularity of polished concrete finishes, providing adequate slip resistance has become an important consideration.
The aspects of a concrete floor or pavement surface that may impact on the risk of slipping include the surface finish, texture and applied sealer (if present). These three combine to produce a final surface roughness. All polished concrete surfaces will provide adequate slip resistance when dry or not contaminated by other substances. The surface roughness of floors should be maintained by regular cleaning to remove any contaminants that may increase the risk of slipping.
The typical concrete used for most residential slabs has a compressive strength of 20 MPa, and is designated as normal-Class N20 concrete.
However, for polished work, the use of a higher strength concrete is recommended: N32 for steel trowelled and honed finishes; N40 for burnished finishes.
The specification of the concrete is only the first step in achieving the desired polished finish; as in all concrete work, the adoption of good site practices is of equal importance if expectations are to be met. All aspects of concrete and concreting are covered in detail in Guide to Concrete Construction. Important points for polished concrete floors are below.
The concrete for any given area should be kept as consistent as possible as minor variations between batches can affect the colour. The incorporation of appropriate joints is a common way of masking any minor colour variations that may occur when concrete from different batches is used in a particular area.
For concrete placed by pump, the priming material used to coat the pump line should be excluded from the finished work as it may cause colour variations in steel trowelled finishes. Concrete should be placed as close as possible to its final location and vibrators should not be used to move concrete. This may result in uneven aggregate distribution in honed finishes.
Adequate compaction of the concrete significantly increases its strength, abrasion resistance and general durability by providing a dense concrete with little entrapped air (from the batching, mixing and placing processes) and lower permeability.
These characteristics also contribute to the reduction of drying shrinkage, thereby minimising the risk of drying shrinkage cracking in the polished concrete finish.
While any deeper sections of the floor/pavement such as edge thickenings and downturns should be compacted using an immersion vibrator, for slabs on ground that are 100mm or less in thickness, adequate compaction can usually be achieved through the placing, screeding and finishing processes.
Sometimes, surface vibration will be used in the form of a small hand-held vibrating screed. Immersion vibrators are not recommended for 100-mm-thick slab-on-ground construction, as the slab depth does not allow proper immersion of the vibrator head, and the plastic membrane (if provided) may be damaged.
For honed finishes, care must also be taken when compacting concrete. The use of immersion vibrators may cause sand streaks in the finish and also uneven distribution of the exposed aggregate in the polished surface resulting in a patchy appearance.
Rectification usually involves grinding the surface to a slightly greater depth to obtain an even exposure of the aggregate.
Care must be taken when finishing concrete that is to be honed. Once concrete is placed it is usually screeded with a straightedge to provide a surface having the specified level and flatness properties.
If the surface is worked too much with the screed to settle the aggregate and fill depressions, the aggregate exposure in the surface may, after grinding, be uneven and there may be lines or sand streaks in the finish. As mentioned earlier, grinding to a greater depth can provide a uniform finish, but not all ways successful.
Avoiding Early Cracking
This Data Sheet summarises the recommendations for avoiding early cracking of concrete. > View
Avoiding Surface Imperfections in Concrete
This Data Sheet covers blowholes, crazing, dusting, flaking, honeycombing and popouts. What are they, what are the causes and how to minimise their occurrence are some of the issues discussed. > View
The sealer prevents staining and should keep the finish looking good for many years. Most sealers will last about five years in a domestic application, with recoating being a simple and economical way to restore the original finish. In wet areas it should generally be removed and replaced to maintain the original surface roughness, rather it.
Note that recoating the surface without removing the original sealer may be an option depending on the initial surface roughness. For areas that remain dry, adding another layer of sealer, similar to floor polish, will not affect the slip resistance of the surface. For solvent-based products, the solvent in the new sealer will allow some re-distribution of the old sealer and hence a more even coat to be applied.
An option to avoid re-coating and a build-up in the sealer thickness over time may be to lightly wipe over the floor with solvent. This redissolves the sealer, evens out the coating and should restore the lustre to the floor. The sealer manufacturer should be consulted regarding the solvent required and compatible sealers.
Note that penetrating sealers are largely protected by the abrasion resistance of the concrete itself and therefore tend to have a good service life.
Many existing concrete floors can be polished to produce a low-maintenance durable floor surface.
The normal approach of lightly grinding the surface to remove stains and minor defects, remnants of adhesive, trowelling marks and to provide a more uniform surface should generally improve the appearance and give satisfactory results.
Since such slabs have not been designed to receive a polished finish and the surface may have been repaired or had sections replaced to run new services, a variable finish should be expected.
Cracks and poor joint details may also need attention. If cracks are exposed, these can either be filled or repaired to reduce their impact, or left as features in the floor.
Depending on the application, they can often add character to the finish. In most cases, people’s attention will not be focussed on the floor, so the overall impression becomes more important than some of the minor details.
Concept™ combines the durability of traditional concrete products with an unrivalled choice of exciting colourways and three contemporary finishes.
Design and build inspirational living areas to reflect all that you value and feel good about in life with Boral polished concrete flooring.
Imagecrete offers an inspiring range of colours and decorative aggregates for you to combine and finish, achieving your chosen style.