January 28, 2020

The Definitive Polished Concrete Guide

The most helpful guide to polished concrete flooring written by industry experts. We go over pretty much everything do with polished concrete.

A polished concrete factory floor

Polished concrete flooring has been highly popular for a few years now and that trend shows no signs of slowing down with more and more new build properties of many different types now opting for concrete flooring within their initial floor plans, from slab on grade builds to raised foundation homes and passiv houses.

There are also a growing number of existing properties that are choosing this durable and low maintenance flooring solution for anything from extensions, garages or for replacing and renewing floors within the general living areas. Concrete patios are a popular option too!

The robust nature and striking contrast between the floor canvas and chosen interior furnishings of the home create a unique aesthetic; almost industrial yet contemporary in feel. Concrete floors polished not only look stunning, they can be highly practical in many residential settings and commercial environments.

In our Polished Concrete Guide by the experts at CARRcrete, we will explain the pros and cons of concrete polishing with the aim of helping you make the right choice of finish, selecting an installer and of course choosing the right polishing expert.

It is fair to say that our guide will be very different to others on the web; you know, the ones that are written by copywriters who know nothing about this subject matter and have the sole purpose of filling a sales representative’s diary? We aim to provide you with something much more factual, practical and in line with our vast experience in the industry.

What Is Polished Concrete?

Before we jump too far ahead, I suppose we should explain exactly what polished concrete is, what it isn’t and what it can and cannot do. There is a surprising amount of confusion surrounding ‘diamond refined polished concrete’ and what it really is.

So let us briefly explain in simple terms. Polished concrete surfaces such as floors, walls, concrete countertops and furniture are all essentially large heavy, rigid slabs comprising of cement, sand, aggregates and water. These ingredients are mixed together either in a ready mix truck for delivery to a building site or locally onsite in a smaller concrete mixer, to form a paste that can be placed into moulds or shuttering or laid to form a floor surface.

As soon as this mixture is brought together, it starts a process called ‘hydration’ whereby the cement begins to gel up and coat the other ingredients in the concrete mixture. The constant rotation of the concrete mixing machine ensures that the cement gel is blended thoroughly with the sand and aggregates. This gel begins to stiffen as time passes and the new concrete begins to set, later forming crystalline bonds which essentially glues everything together.

It is important to realise that all concrete will need to have aggregates incorporated into the mix, whether you want to see these aggregates or not. It is largely how the freshly installed concrete is prepared and laid that determines how the surface will look on completion.

The amount of cement and water is critical to producing a quality concrete, these two ingredients determine the strength, porosity, shrinkage and overall abrasion resistance of the concrete slab. Too much water and the surface will be soft, dusty and highly porous; too little and concrete will be very difficult to put in place and smooth out before it sets.

Concrete can be worked in a variety of ways for a floor surface and one of the most effective methods to achieve a quality finish is to use a power trowel (powerfloat). It is widely believed that a power trowelled concrete is the same as a polished concrete, but this is not the case. The purpose of using a power trowel is to smooth, flatten and compress the concrete surface so that it’s more durable when cured.

Concrete cannot be considered polished until diamond abrasives have been used to refine the power trowelled surface. We do this by repeatedly working the floor with progressively finer and finer grades of diamonds. It is this continual refinement and removal of surface scratches that produces the tight, incredibly smooth, polished finish that naturally reflects light and resists damage.

We do this in combination with using a chemical silicate densifier. This does a number of important things, namely hardening the surface to help with the refining action of the diamonds and also reducing the porosity of the concrete by filling in and forming crystals within the aeration holes that are always present in concrete. Densifying the concrete at the same time as polishing it is massively beneficial to the end user, not only in giving a better overall look but also working hand in hand with any sealant used to increase stain resistance when the floor is in use.

Here’s A Few Regions We Have Worked
But please do not forget we undertake project throughout the UK
Birmingham - Cardiff - Derby - Exeter - Leicester - Lincoln - Nottingham - Sheffield - York

What Are The Benefits Of Having Polished Concrete?

Once a surface has been mechanically polished with diamond abrasive tools and treated with chemical silicate densifiers, the concrete substrate can offer a variety of benefits to the homeowner, store owner or facilities manager.

Concrete that has undertaken the concrete polishing process will be inherently low maintenance with a non-slip surface and in a residential setting, require nothing more than regular dust mopping and the occasional damp mop if required. Commercial and industrial concrete floors would be better maintained with a scrubber drier machine and use of a fine non abrasive cleaning pad with a well diluted pH neutral cleaning product; our PROcare is an ideal product for this.

There are no epoxy coatings to replace, no paint to reapply, no lacquers to sand and replace. Just a hard, smooth, largely seamless surface that is easy to clean. Stain resistance is pretty good compared to other natural products but with added stain protectors, this attribute is greatly enhanced and we highly recommend that all polished concrete is thoroughly sealed with an impregnating stain resistor.

Concrete floors work very well with underfloor heating systems, the aggregates absorb heat and effectively work like a huge storage heater, withholding heat for a good while and cooling down slowly. A heated floor feels amazing under foot!

Finally, the overall long term costs associated with polished concrete is significantly lower than other flooring options that utilise coatings, which inevitably will need to be renewed periodically.

Stain Resistance And Durability Of Polished Concrete

Having spoken with hundreds of clients over the years, the general consensus is that they often believe concrete to be rock hard, unbreakable, difficult to damage and so resilient that it will either never need to be maintained or will simply last forever.

If only that was the truth of the matter! Concrete, like any other flooring option such as natural stone, epoxy resin flooring, timber and tiles can be damaged, stained and abused and still need to be treated with care.

Mechanically polished concrete offers very good resistance to knocks and bangs where objects have been dropped. That is not to say that they are impervious to damage; they are not. However, given that the concrete was of good quality, mixed and laid well initially, it will have an inherent resistance to damage through regular, everyday use once polished.

Resistance to footfall is high and it is typically only the damage from grit and stones trapped in the soles of shoes that creates small amounts of wear. The use of boundary mats is recommended and will significantly reduce the potential for wear and the amount of cleaning required in both residential and commercial environments.

Whilst concrete will not be damaged by falling objects as easily as resin flooring, timber or tiles, it is still possible to dent and chip a polished concrete floor by dropping hard and/or heavy objects. This often shocks clients who have let heavy items fall onto their floor, especially from height. Admittedly, any damage tends to be far less visible than the same damage on another seamless floors, but there may be damage nonetheless.

Concrete can also be etched by almost anything acidic coming into contact with the polished surface. As concrete is a calcium based structure and inherently includes a source of free lime in the concrete’s makeup, there is always a chance the concrete could be damaged by things such as fruit juices, vinegars and fizzy drinks when these are on the surface of the concrete for an extended period of time.

Fats, oils, wines and dropped foods can also stain polished concrete and leave darkened patches if they are given the opportunity to linger on and penetrate the surface. The use of a quality concrete hardener together with a stain resistor will lessen the penetrative aspects of these contaminates but it should always be the aim of the user to clear any accidental spills as quickly as possible.

We use a solvent based penetrating sealant as well as our professional grade silicate densifier on all of our polished concrete projects. The idea is that while the densifier adds strength and begins to seal the concrete from the inside out, the solvent soaks into the pores of the concrete, lining all the sand and aggregates with an ultra fine film of resin. This film of resin sets rock hard, actively increasing the surface tension of the concrete to resist and repel water and oil based contaminants.

We feel it is important to address the term of ‘stain resistance’ overall. There is not a sealant on the market that can 100% protect concrete from staining indefinitely. They all give you a window of resistance and opportunity to remove any spills from the surface. Failure to remove spills within this window will likely lead to either staining or etching of your polished concrete.

Does Polished Concrete Always Look The Same? What Finishes Are Available?

When decorative concrete flooring is mentioned, friends and other contractors will often think of some kind of grey flooring usually with a type of lacquer applied. Thankfully, floor polishing has way more to it than just that, there is a huge amount of skill and knowledge required to refine the surface with diamond abrasives in a productive and aesthetically pleasing manner.

A few years back we created our own concrete polishing concept called InfinityFloor, which is our systematic process for polishing concrete. Like everything we develop, InfinityFloor is continually upgraded and improved as technology advances.

So, let’s go through the three finishes most commonly specified when polishing concrete floors.

InfinityFloor Cream Polished Concrete Floor

CARRcrete InfinityFloor Cream Finish

InfinityFloor Cream, this is a very heavily power trowelled surface. The name ‘cream’ refers to the creamy material that rises to the surface whilst the contractors are working the power trowel. It is this creamy blend of sand and cement along with the movement of the power trowel that produces the appearance of clouds and swirls in the surface that so many find pleasing to see. You will see no aggregate with this look.

InfinityFloor Cream is the one that is most commonly found in Grand Designs and architects brochures, it looks stunning and is highly sought after. We often polish to this specification in new build properties that have the space to get the power trowel into each room before walls are erected and also in industrial settings where the contractors have used large ride on trowels to smooth the surface after laying the concrete.

It would however, be very fair to say that achieving a suitably power trowelled surface is difficult and over the last few years we have found that many experienced contractors have now retired from the trade and therefore the amount of experienced power trowel contractors is sadly dwindling. As a result we see a growing number of floors specified for InfinityFloor Cream that are not installed to a good enough standard and in order to be polished, need either to be ground down (exposing the aggregate) or covered with a micro cement overlay.

When opting for the Cream polish, always ensure you use a professional concrete contractor that has experience in producing a finished floor with concrete using a power trowel. Do not be tempted into saving money by using your builder or ground worker; you will be disappointed.

InfinityFloor Cream can be specified for a matt, satin or a gloss level of refinement and will be sealed with our penetrating sealant for optimal protection.

InfinityFloor Salt & Pepper Finish

CARRcrete InfinityFloor Salt And Pepper finish

InfinityFloor Salt and Pepper. Imagine a Cream floor that has had some of the creaminess ground off to reveal fine particles of sand and the tips of aggregates and you have the Salt and Pepper look. The installation is pretty much the same as a Cream floor in that the concrete floor surface needs to be very flat and smooth and worked with a power trowel.

So with this in mind, please contract a professional to install and finish your concrete inline with our concrete specification to prevent the need for additional works and charges and most importantly to ensure that you receive the floor you’ve desired and imagined.

Our process begins by using a fine metal bonded diamond to gently remove around 1-2mm of concrete material from the surface to expose the aforementioned sands. This action helps to smooth the surface further and remove any minor irregularities before the resin bond tools are used to polish to the desired shine.

A Salt and Pepper polished concrete floor is very industrial looking and often specified for hard wearing industrial and commercial settings where there will be a lot of footfall and fork trucks etc. We have also polished a lot of garage floors where the home owner requires a tough functional floor surface on which to work with their motor vehicles.

Even though Salt:Pepper is of a more industrial look, it can still be completed in matt, satin and gloss levels of reflectivity and is internally hardened and sealed with the same system as used on our other InfinityFloor systems.

InfinityFloor Stone Finish

CARRcrete InfinityFloor Stone Finish

InfinityFloor Stone. This is an exposed aggregate polished concrete, where the surface has had at least 2mm of material ground away to expose the sand and stones contained within the concrete. Exposed aggregates look very similar to the terrazzo floors of old. Incredibly tough, robust and hard wearing, this is often specified for existing floors, newly installed floors that have experienced problems when laid or simply where you want your floor to stand out and be more of a feature in a room.

The aim with a Stone look is to aggressively grind down into the densest layer of the concrete matrix, to get right down into that bed of stone that sits beneath the surface. The exposed aggregate usually has a diameter of 10mm or more, though there will be variations in size and uniformity. It is very difficult to achieve a consistent exposure of stones without a extreme amount of material being removed; lots of grinding is expensive.

The more you grind down, the more the colour of the concrete will be that of the sand used in the mix, varying massively across the country. It is very rare to get a grey stone floor, we’ve only seen this in Wales where slate was used instead of sand.

InfinityFloor Stone still needs to be densified and sealed as mentioned previously, otherwise it will be susceptible to the same damage from acids and oils.

How Are Costs Calculated For Concrete Polishing?

The question we are asked most often - what does polished concrete cost? Very briefly, polished concrete floor costs are determined by the location, size of project, number of rooms, level of gloss and amount of grinding and polishing required. As a rough ballpark figure, you should expect to pay between £40 - £80 per square metre for mechanical polishing. Concrete overlay products start at around £80+ per square metre.

Costs can be reduced greatly be installing the concrete professionally to reduce any additional grinding charges, by erecting dividing walls after the polishing has been completed and ensuring all obstacles such as kitchens and bathrooms are not in place before polishing starts.

How To Install Concrete For A Polished Floor

It goes without saying, if you want a surface that is smooth, easy to maintain and suitable for polishing, you need to have your concrete installed by a professional contractor following a tried and tested concrete specification. We can of course give your installer our well respected specification to follow, unless they already have one they currently use.

We recommend that the mix for a polished concrete slab should be a minimum of C35 grade, which is a good hard concrete supplied to the building site via a concrete mixing truck. We would advise for this type of concrete floor that you do not use a volumetric mixing solution as every floor we’ve worked on that has used this method of delivery has been of substandard mix quality.

It is CARRcrete’s recommendation that you use major suppliers like Tarmac, Lafarge, Hanson etc as their quality control and documentation seems to be far superior to that of small companies.

100mm of slab thickness is a minimum over underfloor heating systems and insulation boards. Laying to this depth reduces the risk of cracking through shrinkage and movement.

The C35 concrete mix should be placed with no added water (which would reduce the strength). The mix should ideally be screeded into place and magnesium floated in multiple directions to remove any tamp lines and to flatten the floor out ready for the power trowel.

An Example Of A Badly Laid Floor

It is really important that no low spots, lines or gouges are left in the surface after the magnesium float work has been done. If the concrete is not flat and smooth the power trowel will not remove any lack of preparation.

The finish the client requests determines how much power trowel work is needed. For example an Cream finish concrete floor needs multiple passes with a trowel to tighten and burnish the surface to produce the cloudy, swirly patterns we often see. This is a highly specialised technique which requires years of experience to master.

Salt and Pepper floors need plenty of power trowel work to compress and tighten the mix but not nearly as much as the cream finish. This is mainly because the surface of a Salt and Pepper floor receives a light grinding before the polishing process.

The Stone finish needs the least amount of work with a power float, but it still needs to be done to ensure the floor is flat, smooth and compact. The act of trowelling the surface helps remove air, breaks down installation marks and lines and overall produces a much better polished concrete floor.

Once the concrete has been laid, is smooth and trowelled to our recommended specification for finished floors, you need to allow any surface bleed water to evaporate before curing the concrete to ensure that it hardens correctly. Curing of the concrete can be done either by covering with plastic sheeting (ensuring that there are no creases in the sheets which could cause curing marks) or by ponding water on the surface.

It is our recommendation that newly installed concrete is left for at least 28 days before any grinding, polishing, densification or sealing works are carried out. Special care should be taken during the colder months of the year as concrete will not cure properly in cold temperatures. Ideally the temperature should be at least 10degrees centigrade for best results. Concrete should never be left to cure on a non-weatherproof site or be left exposed to the elements.

How Do You Polish Concrete Floors?

At CARRcrete we’re always being asked how to polish concrete and the truth is we employ a few different techniques in our polishing process. We often use a combination of wet polishing and dry polishing techniques with our polishing equipment as we have found through years of experience that this allows us far greater flexibility when dealing with all the different concrete mixes we encounter across the country. Most of our projects employ the use of a concrete grinder or a high-speed burnisher.

An Example Of The Diamond Tools We Manufacture For Our Work

In brief, here is a quick overview of our InfinityFloor polishing system, we will at a later date give each finish far more detail in their own article.

For a polished concrete Cream finish we use diamond impregnated fibre polishing pads to gently smooth the power trowelled surface. This very delicate process removes almost nothing from the surface to ensure that the texture and colour of the floor is not erased, while still allowing the diamonds to polish and refine the surface.

As with all concrete there is a quality concrete densifier applied to convert the source of free lime within the concrete to a much harder, less acid sensitive and less porous substance. Once this chemical solution has dried we are then free to continue polishing through the fine grit fibre pads to mechanically polish the surface to a light reflective sheen or high gloss.

After a thorough cleaning down, the polished surface of the concrete is then treated with our impregnating solvent based sealer PROseal. We literally saturate the concrete with this solution so that all the pores of the concrete are fully coated with the stain resistant properties of this product.

The process differs for a Salt and Pepper concrete as we need to be more aggressive in our approach so that the surface laitance material is removed and the machines get down into the tougher sand layers of the concrete itself.

Normally we will start with a relatively fine metal bond diamond to remove 1-2mm millimetres of surface, this may be done wet or dry depending on the concrete at hand. Once we have attained a suitable level of sand exposure, we start removing the scratches created during the initial grinding phase with transition tools, which again can be a wet or dry process.

After the transition phase, resin bonded diamonds from 200 grit up to 1500 grit are used to hone and polish the surface to the desired level of light reflectivity and gloss. Silicate densifiers are used at multiple times during the polish process to ensure the highest level of robustness are achieved and the floor is finally sealed with PROseal to help protect against stains.

InfinityFloor Stone polished concrete is the same as the Salt and Pepper system but with a lot more coarse grinding to remove at least 2mm millimetres of concrete mass. This process gets down into the hardest regions of the concrete mix, where all the larger aggregates reside. The more material you remove the more uniform (in theory) the aggregate exposure is although this is not always the case.

Please bear in mind, lots of diamond grinding is expensive! A well mixed and well laid floor will always save you money in the long run.

What Colour Is Concrete? Are There Different Colours Available?

This is a very common question and most people when asked seem to think that concrete will always be a shade of grey. Whilst there is usually a grey cement added to the concrete, it is by proportion a very small percentage of the overall mix. So, more often than not, concrete is the colour of the sand used by your local concrete supplier, unless you request a colour pigment to be added to the mix.

If you require a specific tone or colour we would always recommend the use of a pigment or alternatively have a concrete overlay applied. Both of these options will get you closer to an actual colour palette than waiting for your concrete to be ground and polished only to find out it is a shade of beige as opposed to grey. We do not offer any stained concrete services purely because the results can be very hard to predict and vary across the country according to different mixes. Concrete is certainly not an exact science.

There is a wide range of colour tones available for concrete mixes and overlays, most are based around iron oxide powders but there are also liquid nano dispersions available; everything from reds, pinks, blue, green and yellow through to greys and blacks. Using white cement instead of grey can expand the colour range significantly, though availability is largely down to your supplier.

Can An Existing Concrete Floor Be Polished?

If you have an existing concrete slab for example in a garage, workshop, commercial or industrial premises it can usually be polished. The final outcome is large down to the quality of the installation, condition of the concrete and indeed the quality of the concrete used.

It is very rare to find an existing slab that is suitable for a cream polish as most floors do not have the amount of power trowelling required to create the cloud effect that is desired. It is also common to have to utilise the grinder to remove surface contaminants and built up dirt associated with past use therefore most existing floors end up with a Salt and Pepper or exposed Stone.

As mentioned previously, taking into account the condition of the concrete you want polishing is really quite important. A poor installation rarely lends itself to a premium concrete polishing process or outcome and will often eat into your budget.

We design and manufacture our own repair products for concrete slabs which can be used to patch up holes, cracks and damage to concrete that is already in place. Please bear in mind that while repair products may get close to same colour as the surrounding material, it will never be exactly the same and variation should be expected.

Can You Use Underfloor Heating With Concrete?

Yes indeed! In fact we have found that most slabs laid in the last couple of years are over water fed underfloor heating systems. We would say that the most important factors to consider when installing concrete over UFH is that the concrete is laid to a depth of at least 100mm and perimeter movement joints and crack inducement joints are cut or placed when necessary.

It is also highly important to commission your underfloor heating system in the correct manner, after polishing has taken place, by raising the water temperature slowly and over a number of days to reduce the risk of cracking. This gives the huge rigid slab that are concrete floors time to slowly acclimatise with the heat running through it. From experience we have found that floors which have a surface temperature of 35 degrees Celsius or less experience the least amount of problems from cracking, shrinkage and signs of deterioration.

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