Is it best to polish concrete wet or dry? This is a question that will have to be asked before each job. The condition of the concrete floor, the environment it occupies, the desired look of the finished product, and other expectations and preferences will all play a role in this decision. Many times, it may be best to use a combination of wet and dry polishing.
Wet polishing is the oldest form of polishing. Natural stone is most often polished wet and has been for centuries. In the earliest days of concrete polishing, the floors were polished wet. Over the years, it was discovered that dry polishing increased the level of shine, and equipment and tooling was created with dry grinding and polishing.
Dry grinding has been the most popular method in the United States over the past decade, but wet polishing has made a significant resurgence as part of the "go green" craze and with the bid process becoming more and more competitive.
There are disagreements over which method is greener. Dry grinding solves the disposal problem much more efficiently, as the disposal of slurry can be a problem. The regulations on slurry disposal vary from one jurisdiction to another, and regulations should be researched before any slurry is disposed of. Contractors need to have the proper wet-vac systems, which can be purchased or rented.
Wet grinding solves another environmental problem, silicosis. Wet grinding and polishing eliminate the dust clouds that can come from dry polishing. Asbestos became a huge problem for the flooring industry, and silicosis has the potential to become a similar problem for the concrete polishing industry. Even with a large dust extractor in use, workers can inhale a great deal of dust when concrete is polished dry.
When dry grinding, workers should be instructed to wear protective masks, and masks should always be made available on job sites. Also, special care should be taken in retail environments, as well as environments where customers or workers of the facility are around while the work is being performed. Dust in retail environments also needs to be cleaned up at the end of each day and not left on merchandise.
Wet grinding and polishing also increase diamond life dramatically on medium-hard to very hard floors and allow for more aggressive grinding. Wet grinding can be very effective when trying to remove a significant layer of concrete to expose aggregate. It allows the diamonds to cut faster on medium-hard and very hard floors. Any contractor who has been asked to expose aggregate knows it can take a long time to grind an entire slab down to larger aggregate, taking out high spots and exposing aggregate as evenly as possible. Wet grinding creates more friction and, more importantly, keeps the diamond tooling cooler, which prevents metal bond tooling from glazing over. Using water in the first two or three steps of polishing helps remove scratches left behind by the metal bond diamonds. The floor can be finished out using wet polishing in the higher grits for a duller, easier-to-maintain shine level.
However, dry polishing will always give the floor a much higher level of shine than wet polishing. It will provide a much higher level of light reflection and a classier-looking floor. Dry polishing will also always work better on a soft concrete floor, which can wear even the hardest diamond bonds out far faster than expected, causing job costs to surge and profits to dwindle. While polishing wet on these floors, the diamonds could be overaggressive and leave gouge marks in the floor.
It is not necessary to do a whole job using one method or the other. It is possible to grind wet and polish one step wet, then polish dry to get a high shine and still keep costs and dust under control. The last few steps of polishing leave behind very little dust.
Quality concrete grinding and polishing require an experienced contractor. They require a contractor who knows what is best for his customer and who is not overly dependent upon the advice of vendors, who have to take their own best interests and profitability into consideration as well as those of the contractor. Concrete polishing is a young and evolving industry. It is too early to make absolute and permanent determinations of any kind. Contractors need to take control of their own destiny and always be reeducating themselves. They need to always think of their own profitability and exposure and weigh the best approach on each given job.
Contractors also need to play a role in the education of general contractors and end users, and not leave this task entirely up to the vendors supplying the concrete contractors, as the contractor needs to make certain his best interests aren't left out of the equation.
The smaller and newer contractors in the concrete polishing industry need to take extra-special care to continually educate themselves on ways to provide a nice polished concrete floor faster, cheaper and better. Larger and more established contractors are controlling a larger and larger percentage of the work being done, especially the big work being done. They are established and have more negotiating power with vendors. They have the leverage to be recommended by the vendor for large jobs, especially jobs done by chains and on a national level. Without intending to do so, vendors can become virtually aligned with certain contractors. The system snowballs as the vendor aids the largest contractors and the largest contractors become larger and larger and obtain an ever-growing influence over the vendors. This can't be avoided in any industry. Margins are dwindling, especially for the smaller contractor, so the smaller contractor needs to be especially open-minded about cost-controlling methods that will allow him to remain competitive.