Polished concrete is becoming extremely popular finish virtually in every type building whether residential, industrial, or commercial establishment is the ideal choice. What many people are not aware of is that not every concrete floor slab can achieve the optimum appearance.
A professional concrete floor polishing company have many tricks in its tool box to fix certain imperfections when found during the grinding or polishing process, but what no polishing company cannot do is perform magic. Unlike going out to granite shop for a new granite countertop or floor, where you can pick and choose the granite slab which has been polished and ready to be cut to size to sit in the kitchen, the concrete slab that is in place that you want polished is what the concrete polishing company has to work to get the best polishing results out of this slab. Having said that, it has been out experience working in the greater Toronto area, is that better than 93% of concrete slabs we encounter will produce a beautiful polished concrete floor. We have also observed a new trend mostly in lofts and older office building in downtown Toronto, which originally started and became very popular in New York and now our Toronto based clients actually prefer lots of imperfections we find in concrete slabs that are older than 60 + years, as it adds character and modern charm to the appearance of the floor.
Many new builders, architects, home owners who are involved in building new projects with polished concrete floors as part of their plan, are not aware that there is some planning required for their cement mix which will form the floor to be polished. Below we will discuss things to be aware of when planning polished concrete floors in new buildings or homes.
Although currently there are no specific industry standards specifying concrete tolerances specific to polished concrete, the concrete polishing professionals are coming up with their own set of standards to obtain an optimum quality polished concrete floor. On new concrete installations that will ultimately receive the polishing process, certain criteria needs to be met so the polishing can be performed in a uniform quality.
On new concrete installations, the concrete mix design is critical for optimum end results of polishing. Using a cement-rich concrete (typically 3200 to 3,500 psi) provides a dense surface free of voids for the polishing process. Usually water-reducing admixtures keep a low water cement ratio without jeopardizing the workability during the concrete pouring and placement. Wet curing of the new slab is an excellent way of curing but many times is not practical. If this is the case, dissipating liquid curing compounds application is a very good way to cure the concrete floor slab. Should any remaining curing compound that does not dissipate prior to polishing is usually easily removed during the initial coarse-grinding phase prior to the polishing process commencement.
Equally as important to the appropriate cement mix design is how the cement is poured and finished. The flatness and levelness of the concrete substrate is critical not only for a uniform polishing finish, but also how the project is priced. Floors that have excessive highs and lows will require a tremendous amount more grinding, increasing labour costs as well as the costs of diamond tooling which is required to grind and polish.
According to concrete industry standards, finished concrete slab shall have a minimum Floor Flatness rating of minimum of 40. Industry standard for terrazzo flooring is no more variance than 1/4 in. in a 10-ft. span, which could apply to polished concrete as well. If the new poured concrete floor is machine troweled with walk-behind equipment, it is imperative that the contractor is aware that the slab will serve as polished concrete and to not leave any indentations or boot marks behind since they are not easily removed during the grinding or polishing phase.
The most common methods of colouring concrete floor which will be polished can either be integrally colouring the concrete mix at the source or dyeing the surface after the fact after the grinding phase or prior to the polishing phase. By far the easiest and most controllable method of coloured concrete is to have the cement mix integrally coloured by the cement mix supplier prior to the pour. Most integral colour is either in the liquid or powder form and added at the ready-mix batch plant and then mixed for a specified time. Colour loads for integral colour should never be smaller than 3 cu. yds. for colour consistency. Coloured aggregate or crushed glass can be added to the concrete mix or hand seeded into the top layer of the mix by the new concrete slab finisher and power troweled. The grinding and polishing process will reveal the underlying aggregate placed in the mix.
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