Polished concrete floors burst onto the construction scene a few years ago, and have gained in popularity ever since. They are one of the few areas in construction that continue to grow despite the down economy.
One reason is that because you don’t have to strip or replace them, polished concrete floors can save a lot of money over time for schools, hospitals, stores, and any place where you keep an eye on the maintenance budget.
Another reason is that they can be drop-dead gorgeous.
Here’s a quick look at the basics of creating these remarkable floors.
Grinding/polishing procedures depend on individual floors and conditions. In general though, it’s like sanding wood.
Grinding starts with coarse diamond pads to grind the floor and proceeds to ever finer grits until you get the polish level you want.
At some point, usually around 200 grit, you switch from “metal” bond diamond-impregnated pads to “resin” bond diamond impregnated pads. The difference is that the metal bond holds the diamonds more firmly on the pad, which gives a more aggressive cut, for grinding and removing more floor material.
The resins hold the diamonds less firmly and are less aggressive. Combined with finer grits, they remove less material and provide a shine.
Grinding usually starts with metal-bond diamonds as coarse as 30- or 50-grit. You work up to about 200-grit, then switch to resins. Your first cuts with coarse resin-bond diamonds of 100- and 200-grit are the last steps in grinding. Polishing is usually considered to begin with 400-grit resins.
If you’re going to color the floor with a water-based or acetone stain, this is a good point in the procedure for the first coat – after the grinding but before the polishing.
You increase the efficiency of the polishing by hardening/densifying the floor at the point where you finish grinding and begin polishing – typically where you switch to resin bonds from metal, but after that first color application if you’re using color.
Harder, denser surfaces polish faster and easier because of the increased surface area and decreased porosity. But they also make it harder for the color stains to penetrate, so harden/densify after the color goes down.
Older sodium- and potassium-silicate hardener/densifiers require scrubbing in, flushing, and wastewater collection. Newer lithium-silicate hardener/densifiers can just be sprayed on with a pump-up or automatic sprayer, and then spread out with a mop, brush or pad.
Another benefit of hardened/densified floors is that they don’t generate chalky concrete dust. That makes them an ideal treatment for warehouse floors, polished or not.
You continue with ever finer grits of diamond-impregnated resin pads until you get the level of shine you want. Real gloss starts showing around an 800 grit finish, but higher finishes, 1500 to 3000 grit can impart an almost mirror-like shine. If you want deeper color, put down another coat before the final polishing pass.
Once you’ve got the finish you want, you must protect the floor – especially if you used color.
You can use either film-forming or penetrating treatments. At lower grit levels, like 800, some film-formers can give you an extra level of shine, saving you some polishing time and effort.
Most film-formers need to be replaced or refreshed periodically, since they show wear and traffic patterns. The best are actually burnished in to “meld” with the concrete, so don’t ever need to be stripped and replaced. Simple re-application and burnishing – often, just burnishing alone – is enough to “pop” the shine.
Burnished-in treatments are the best choice if you colored the floor. Some colors can remobilize and run if they get wet when the floor isn’t protected.
Your other choice is penetrating protective treatments. These will not add any gloss or change appearance or texture in any way. They penetrate and repel water – some also repel oils – from inside the concrete pores. There are highly penetrative treatments that work even on hardened/densified concrete.
Because penetrants work from below the surface, they’re much less subject to abrasion from traffic than film-formers – even burnished-in film formers. They have a lengthy service life, easily measured in years.
Whether you choose film-forming or penetrating protective treatments depends on the kind of floor and the environment the floor must deal with. A warehouse, with heavy traffic, for instance, would probably take a penetrating treatment, whereas a museum with lighter foot-only could use a film-former.
Either way, a protective treatment is important, even crucial to the long-term durability of the finish.
It’s a common myth that finished concrete floors are “no maintenance.” They are low-maintenance, and unlike some flooring types such as carpet and VCT, will last the life of the building.
Like anything that gets traffic, concrete floors need regular cleaning and attention – just not as much other flooring types.
But that’s another story.