Technical Information for Polished Concrete

What is Polished Concrete?

 

Polished Concrete

It was once confined to the stone and terrazzo industries only, but today it is widely used in residential, public sector and commercial buildings.

From gigantic stores like Wal-Mart to corporate offices, schools, hospitals, churches and private residences, polished concrete floors are everywhere. High-tech concrete floor polishing equipment is used to make concrete surface shine and gleam. However, polishing a concrete floor isn’t a piece of cake. It needs specific skills and experience. Thus, it is recommended that you use a experienced polished concrete flooring contractor.

Polished concrete is concrete that has been treated with a chemical densifier and ground with progressively finer grinding tools. The grinding tools are progressive grits of graded diamonds and diamond polishing pads. Typically, concrete is not considered polished before 400 grit has been applied, and it is normally finished to either an 800, 1500, or 3000 grit level.

 

The demand for polished concrete floors is growing worldwide. The process of polishing concrete with a concrete floor grinder is similar to refinishing wood with a floor sander. Concrete grinders are used to gradually grind down the concrete surface using a combination of metal bond diamond abrasives followed by resin bond diamonds to achieve the desired shine and smoothness.

 

Polished concrete is considered a good sustainable design option because it makes use of the materials already present. Most modern buildings are built on or with a concrete slab; polishing the exposed concrete eliminates the energy and material consumed by applying a floor covering. It is something to consider when building or modernizing towards a more green solution.

 

Polished concrete floors are low-maintenance, as they are more durable and easier to clean than many flooring options. Its relatively high coefficient of friction can make it non-slippery. Polished concrete reduces dust mites and allergen problems, and does not support mould growth. Anecdotal evidence suggests highly reflective polished concrete reduces lighting needs and improves natural lighting. Polished concrete flooring is hard wearing and will not naturally chip or dent like softer surfaces such as timber. Mopping with warm water and flooring conditioner once a week is the only maintenance required. A concrete floor that has been hardened and polished will have an extremely long life expectancy compared to other flooring. For example, tile that may only last 10–20 years(tile is a vague term. porcelain will last hundreds of years with no maintenance), but a polished concrete floor that has been properly maintained may give 100+ years of service.

 

What Guarantees do we get?

  • We do guarantee your floor is bespoke to your project.
  • We do guarantee a minimum 10 year dust free surface.
  • We do guarantee a minimum gloss reflective surface of 65 GU using test method for 85° specular gloss of emulsion floor polish
  • We do guarantee a minimum slip resistance level of 58 dry & 36 in wet as measured with a pendulum slip tester and applying temperature variant of -3 points.
  • We do guarantee a minimum compressive strength 35N/m2
  • We do guarantee the lifespan of your floor is a minimum 20 years with the correct cleaning and maintenance.
  • We do guarantee the abrasion resistance of a minimum AR1.
  • We do guarantee a stain resistant surface when our cleaning and maintenance instructions are followed.
  • We do guarantee all our products used in the creation of your floor are sustainable and ecofriendly.
  • We don’t guarantee your floor will be as flat as a snooker table
  • We don’t guarantee that aesthetically it will be pleasing to all (beauty is in the eye of the beholder)

 

What makes us Different?

From a simple scrubbing and sealing flooring solution to grinding, colouring and polishing, polished concrete floors have come a long way from its origin. Many products are available that work for BREEAM points and promote virtually zero percentage waste. We use UV-stable colorants in order to harden and densify the concrete.

 

All our polished concrete consists of a considered concrete mix design, proven finishing and curing processes, grinding, honing, densifying, polishing and the application of stain guards in order for us to produce the finished product.

 

In 2007 I was asked which changes or advancements have had the biggest impact on polished concrete floors, primarily in the industrial and commercial market sectors.  Although we could discuss equipment improvements or how diamond tooling technology has significantly advanced through the years, the biggest impact by far is how concrete slabs are poured and treated from the ground up.

 

This first became apparent, when another contractor asked that we polished a floor that they had installed to evaluate the floor, we attended site and it was immediately obvious to us that the floors were not being poured with polishing in mind as the surface was very coarse with aggregate exposure. The polishing time was extended from 1 week to four weeks to achieve a finish acceptable to the client.

 

To improve the overall quality of the polishing, we needed to start by improving the quality of the concrete and its placement, especially how the slabs were being finished, cured and protected during the construction phase. That’s when we decided to bring the installing of the concrete in-house.

 

Today, there is now a heightened awareness of all of the team players involved in producing these floors, and it has dramatically helped to improve the overall quality of polished concrete. It can still be very challenging to work with the various trades and recommend that they perform their work in a way that deviates from the industrial floor norm and standard routines.

 

The new plan

Concrete finishers can be notorious for being set in their ways, and often they don’t like outside sources asking them to finish a slab a certain way. Being a fourth-generation finisher floor layer myself, I appreciate this mentality and I love how most finishers consider themselves artists and take an attitude of ownership of the slab they are finishing. Finishing crews are accustomed to burnishing the slab to the point of darkening the concrete and obtaining a high shine, and they will often wet cure the slab with blankets for three to four days to increase the overall strength of the floor. This combination of wet curing and a burnished slab can wreak havoc with polishing contractors, who will typically need to use their most aggressive diamond tooling combined with wet cutting to expose the appropriate amount of aggregate. We have found that producing a “haze” or “smoke” finish, with little if any sheen or burnishing, is more conducive for Exposed polishing. But the burnishing of slabs whilst finishing provides the best Refined polishing finish.

 

We recommend a pre-slab construction meeting specific to the installation and polishing of concrete floors be arranged and all key people attend. In addition to the key people, including the owner’s representatives, general contractor, concrete subcontractor, UFH subcontractor and polishing contractor this is helpful to plan and design joint positions with the UFH team, concrete installer and polishing contractor, other members of the team that can have an impact are plumbers to agree manifold positions and feeds, plasterers and electricians as there are many different ways to protect concrete floors from general use and abuse their attendance helps in the understanding of how fragile newly laid and polished floors are.

 

Polishing V’S Coatings

There are many different ways to protect concrete floors from general us. We compare floor coatings to penetrating liquid chemical hardeners. Let’s compare four basic methods of floor finishing and protection. Each has its own characteristics, advantages and disadvantages. In order of discussion, they are:

 

Chemically resistant epoxy coatings and moisture-cured urethanes, referred collectively as “thin film coatings”

 

The old saying goes, “Beauty is only skin deep.” If that’s good enough for you, then there’s no better skin than epoxy or urethane floor coatings. In fact, that’s exactly what it is: a skin of hard epoxy or urethane resin that protects the top of your concrete floor. Thin film coatings are shiny, colourful, very resistant to chemical attack and stains, and generally resist dusting. But, like all things that are skin deep, they don’t always age well. Buying an epoxy or urethane floor is a lot like buying a new car. It’s great when you drive it off the lot, but you can’t keep that new-car look forever. While thin film coatings are durable, by their nature they are only temporary. As time goes by, these coatings begin to discolour and show scratches, cuts, chips, and general wear. Depending on the punishment your floor is going to endure, predicting the life of a thin film coating is difficult. Generally, you can count on two to five years. If you’re lucky, you’ll get by with a sanding and a thin topcoat. But if the coating has deteriorated badly, you’ll pull everything off the floor, remove the old coating and put down a new coat.

 

Conventional floor waxes

Bottom line: Thin film coatings are great to look at and very durable in the short run. But the long-term cost can be high, and they are costly and difficult to remove and replace.

 

Floor Wax

Want your floor to be shiny? Put wax on it. Want it to be shinier? Put more wax on it. The more you put on, the shinier the floor gets. But the absolute irony about wax is that the more you use, the worse it is. The heavier the coat (or coats) of wax, the more vulnerable the floor is to scratching, cutting, scuffing and general wear.

 

Are there any advantages to waxing a floor? Yes. It looks like you’re saving money and it might seem to be a pretty easy sell to the bean counters, because wax sounds cheap.

 

But in reality, wax is very expensive. Each cycle includes removal of the previous coats and application of the next new coat or coats, only to be repeated again and again. Figure the 30-year cost on this and you’ll be surprised at how expensive it is. When calculating the cost of waxy build up, you must also remember that wax is doing little, if anything, to actually protect the surface of the concrete floor.

 

Chemical hardeners and densifiers,

The major brands effectively eliminate dusting and create a fairly nice appearing floor while maintaining the natural slip resistance of concrete. While they are certainly a great improvement over bare concrete, densifiers cannot deliver the shine of an epoxy or urethane. Treated floors, however, develop a medium, easy-to-maintain sheen when regular maintenance discipline is followed. We have found that if the concrete floor surface isn’t perfectly smooth to start with, the potential visual appearance of a chemically hardened and densified floor will be compromised.

 

The big advantage to these products is once they change the molecular structure of the concrete in the top surface to be harder and denser, the change is permanent. That makes maintenance from that day forward simple and inexpensive. Thin film coatings and waxes just lay there on the floor waiting to wear off. In contrast, a chemical densifier with proper care (adding conditioner to water before mopping) reduces the long term maintenance costs and promises low cost, long-term performance that is clearly superior to other treatments.

 

We give the thumbs up to liquid hardeners that change the molecular structure of the near surface wear zone, making it denser and stronger. The slip resistance remains unchanged from the original bare concrete. Since liquid hardeners do not leave a film, they are dependent upon the finish of the concrete for visual appearance. Therefore, they are not as glossy as newly applied epoxies, urethanes or waxes. A treated floor will nonetheless be more durable and will maintain its dustproof protection for a very long time.

 

Densifiers

Continuous innovations are taking place in the concrete floor industry, and densifier isn’t an exception. Ideally, manufacturers recommend these products as hardeners. Densifier has several benefits; it hardens the surface, prevents surface dust, and most interestingly, increases slip-resistance.

 

Growing environmental awareness has integrated some more steps, like containment, collection, and standard disposal of waste, in the concrete floor making process. These newly added steps have considerably improved stain resistance, abrasion resistance and dust prevention in concrete floors.

 

The 21st century has made communication easier, faster and streamlined, and polished concrete has not been left behind!

Abrasive smoothing, grinding, and polishing old and new concrete floors is not simply a method for protecting a concrete floor-it is a process for making any concrete floor incredibly dense, smooth and visually appealing. It is the concrete equivalent of fine sanding hard wood.

 

Our process consists of a series of abrasive smoothing steps that, when completed, produces an impressive concrete floor surface, both visually and in terms of durability. When the grinding and polishing steps are combined with the application of a compatible, liquid chemical densifier, the result is a smooth, glossy, durable concrete floor. It produces a light reflective floor that is exceptionally resistant to wear, dusting, marking and abrasion.

 

Our employees maintain a uniformly high quality standard throughout the industry. Our process begins by testing the concrete before grinding and smoothing a concrete floor with diamond-impregnated abrasive discs that are fitted to large, heavy floor grinding and polishing machines. Depending upon the original condition of the floor to be treated-what the installers call “ground zero”-the first step of the process typically begins with coarse diamond pads that level the floor surface for Exposed Polished. The process then moves through a succession of steps using progressively finer diamond pads also used for Fine Polished, increasing the smoothness of the floor with each step to profession pads also used for Refined Polished (similar to progressing from coarse to fine sandpaper when one finishes wood). The original condition of the floor and the desired level of finished polish determine the selection and number of steps. With the assistance of a factory-trained installer we produce a low maintenance, slip resistant, anti-static, dust free and light reflective product.

 

After completing the abrasive smoothing steps, the final step of the process is to apply a high-performance chemical stain resistant densifier. We’ve already talked about similar products in the previous section. In our previous discussion of chemical hardeners, we pointed out that the visual results are dependent on the original condition of the floor. But with the stain resistant process, the resultant floor becomes very smooth and reflective. The use of the chemical treatment is necessary to penetrate, densify and harden the exposed cement paste located in the top 3mm of the floor. The resulting shine of the smoothing process is quite impressive, and takes concrete floors to a new light reflective level.

 

The importance of the chemical densifier cannot be overstated. Its purpose is to hold that shine and to add many years to the expected life of the floor, an important factor when considering the significant cost incurred in preparing and polishing the concrete surface.

 

Our high-tech vacuum air filtration eliminates virtually all airborne dust.

 

There is some debate about whether the grinding process should be done “wet” or “dry.” Historically, stone floors and terrazzo concrete have been ground wet, a process that produces a significant amount of wet cement paste or slurry during the coarser grinding steps that must be properly disposed. After a careful review of the old methods, and a thorough analysis of the available grinding equipment and vacuum systems, we concluded that both have merit and given that all floors are not made equal we endorsed both systems which we incorporate using 5 manufacturers. As we state not all floors are made equal and even though we test all concrete before polishing sometimes differing methods are required. Whilst we have tested many machines from several worldwide manufacturers, we have found that there is not to our knowledge one machine or one manufacturer that suits all floors, given this information we have selected what we feel are the best 5 worldwide and utilise the technical knowledge of all in producing our floors.

 

Old concrete or new concrete

Our processes are effective on old and new concrete. The upside here is that most aged concrete floors can now be economically rejuvenated with the system. Once the floor has been renewed and a regular maintenance program is adopted, you now have a floor that is low maintenance, slip resistant, anti-static, dust free and light reflective and will last for decades instead of years, with a very affordable amount of care. Regular washing with a specially prepared, concentrated cleaner and conditioner solution is all that’s needed to keep the floor in first class condition.

 

Lowest Maintenance – Key to Success

Certainly polished concrete floors require periodic maintenance like other flooring solutions, but the techniques used to clean these floors are the cheapest methods possible. Moreover, these floors last longer, at-least 20 years. A great variety of colours and designs are also some of the reasons why polished concrete floors have gained so much popularity today.

 

Cracks and Crazing

Whilst every effort is made to eliminate cracks, this cannot be guaranteed. The reason behind this statement is that although we place or insert movement joints, the positions of these joints are calculated using information collect over many years by the engineers and technical folk within the concrete industry. They have calculated tensile stress that is created as concrete drying and measured this against tensile strength of the concrete to determine the most likely fracturing (cracking points). This is where we place the joints to help compensate for the stress. We also consider re-entrant corners and obstacles within the floor, either aligning the joints to the obstacle where possible or increasing the tensile strength in this area by incorporating bars or extra reinforcement. You may ask why not add more joints? The reason is a simple one, we follow an aspect ratio of 1.5 -1 where possible with a max width 40 x depth. If we add more joints the aspect ratio changes and adds the need for more joints and so on. Cracks are also caused by sharp changes in temperature and wind blowing across the surface. Whilst the list of reasons is not exhaustive these are the main reasons found behind most cracked floors. If the floor should crack the likely hook is that the cracks will not be of a structural failure nature as the concrete is reinforced to hold the floor together in this event. Although the cracks can never be hidden, the can be filled to the level of the surrounding concrete and polished. As at the beginning of this paragraph every effort is made to avoid such cracking but due to forces beyond our control cannot be guaranteed. The concrete society state within TR34 section 5.5 cracking “it is difficult to be certain that a floor will be completely crack free”. Cracks that are evident in these types of floors will not be of a structural nature and after the initial shrinkage if they do not appear to be getting wider or flexing under foot traffic loading. These should be monitored as suggested in TR34 as part of the maintenance and cleaning regime. If the cracks do start to decay or spall then they will require evaluation for treatment as described in TR22 none structural cracks in concrete.

 

Every effort is made to avoid crazing at the surface but not guaranteed; this is common on concrete floors and is more visible when wet and these fine cracks trap moisture and dirt. TR34 5.6 Crazing states “crazing is considered to be a matter of appearance only and generally no structural or serviceability issues are associated”. The mechanisms of crazing in floors are not fully understood and as such no recommended measures are available from concrete society that can reduce its occurrence.  TR34 5.6 Crazing states “there is no appropriate treating for crazing and so if this feature is unacceptable to the user, provision should be made at planning stage for over-painting but this will incur on-going maintenance cost”.

 

Summary

Every effort will be made to eliminate shrinkage restraint cracking and crazing, however this is not guaranteed. In the event that cracking or crazing occurs we will ensure the floors structural integrity or serviceability are maintained.

 

Gloss Testing Comparisons

Gloss-Testing-Chart

 

What is a Pendulum slip test and how does it work?

Slip Resistance Certificate on Polished Concrete Floor – Click here to see our slip resistance test certificate.

 

In layman’s terms the Pendulum slip test gives a definitive answer whether your floor is fit for purpose under foot when wet or dry. The instrument stands about 2 ft high on a tripod that takes up 1 square meter. A horizontal arm is released with a rubber shoe on the end. The sprung loaded shoe hits the surface and stays connected to the floor for 127mm carrying a marker that resembles a needle. This needle then travels through the numbered scale and stops at the given level of resistance. It’s this reading that determines the suitability of the surface.

 

Our Polished Concrete Floors achieve 66 when dry and 36 when wet.

 

HSE Guidelines:

Pendulum Test Value (PTV)

0 – 24 High Risk

25 – 35 Moderate risk

>36 Low Risk.

 

 

Proposed Floor Make up for 75mm Polished Concrete with Under Floor Heating.

75mm With UFH