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polished-concrete

Frequently Asked Questions - How to Grind, Polish and Maintain Floors 

More articles and how to information about floor grinding, polishing and maintenance

Why polish concrete?

Polished concrete has many advantages: it is durable, easy to maintain, cost effective, dust proof, LEED friendly, has increased light reflectivity, and is slip resistant, among other benefits.

  • The life expectancy of a concrete floor will far surpass that of most other flooring surfaces, making it a common choice for warehouses, manufacturing facilities, large stores, schools, hospitals, and government buildings. Polished concrete floors are also becoming more popular in residential homes.
  • Durable enough for heavy machinery, forklift activity, and extensive foot traffic, polished concrete is easy to clean, requiring only occasional mopping.
  • These floors also eliminate the need for special waxes or  coatings, as well as the associated labor, time, and expense to apply them.
  • Polished concrete floors are generally no slicker than untreated concrete surfaces and are about 40% less slippery than a hardwood floor, waxed linoleum or polished marble.
  • The high light reflectivity of polished concrete is another important aesthetic benefit, especially for office buildings, hotels, restaurants, and other public facilities that want to project a bright, clean, professional image.
  • Furthermore, polished concrete may be stained, stenciled or engraved to add character and further improve its appearance. The available options for coloring concrete have never been greater, and there is also an endless array of other decorative effects. In short, polished concrete is a popular flooring solution because of its practical advantages, as well as its decorative appeal.

What do I need to get started in concrete polishing?

We recommend a complete surface preparation system including: a floor grinding and polishing machine(s), vacuum system(s), diamond tooling, chemicals (densifier and sealer) and dyes (optional). It is also important to receive proper training to ensure that your projects are completed in a professional, timely and cost effective manner.

Where can I get trained and certified on the LAVINA system?

Superabrasive's LAVINA distributors offer floor grinding and polishing training classes at various locations many times throughout the year. See SCHEDULED TRAININGS / DEMOS or contact Superabrasive for details at (800) 987-8403. Typically, LAVINA trainings are two day, hands on classes, and cover topics such as: concrete floor prep, polishing process steps, chemical applications, diamond tooling options, burnishing, etc. 

Which floor grinder and diamonds should I select?

Choosing the proper floor grinding and polishing machine and diamond tooling is critical for the success of the job, and the following questions should be addressed first:

How big is your project, and how much time do you have to complete it? This will determine the size of the grinder and vacuum needed, as well as how much tooling will be required. For example, a LAVINA 20 (20 inch) is appropriate for small residential projects, like garages or patios, whereas larger commercial projects will require a larger, more powerful machine such as LAVINA 30 or 32.

How old is the concrete? Freshly poured concrete floors require at least 28 days to cure. Conversely, older concrete should be inspected for pits and cracks, which may be treated by a product such as Quick Mender®.

What condition is the concrete in? The condition of the concrete will determine the initial grinding steps needed to prepare the floor for polishing which include coatings or epoxy removal, etc. If the floor is in optimal shape, you could start with 120 grit metals, but if the floor is uneven and blemished, you should begin with a coarser grit, such as 30.

How much aggregate would you like to expose? If you want to show aggregate, you must grind the concrete more aggressively (longer and deeper) than if you simply want to polish only the cream.

How hard is the concrete? Typically concrete under 2500 psi is considered soft, between 2500-4000 psi - medium, 4000-5500 psi - hard, and above 5500 psi - extra hard. We recommend testing the concrete hardness of the floor prior to selecting diamond tools. A popular and easy to use tools for testing the concrete hardness is the Moh's pick set (scratch tester).  

How much shine do you want? If just a honed finish with less shine is desired, you may stop processing the floor after grit 400. However, a shiny and mirror-like finish will require processing the floor to a much higher grit - typically 3500. For maximum shine, you can go up to 8500 grit resin, such as Superabrasive's V-Harr BUFF pad.

Grinding wet or dry? This will sometimes depend on the job and job site. Most operators prefer the dry process, as it requires less clean up; however, wet grinding is best for some applications. Keep in mind that dry grinding will always require a vacuum for dust removal.

Is your project indoors or outdoors? This will determine which sealer and dyes are needed. Some guards and sealers are appropriate for indoor applications only. Water- and acetone-based dyes are also for interiors only because they are not UV stable. Others such as ColorJuice™, however, is UV stable and ideal for concrete porches, patios, driveways, sidewalks and pool decks. Contact us for additional information about your specific job and the appropriate chemicals to use. 

Choosing the right diamond tools for a floor grinding and/or polishing project

Understanding how diamond tools work is a must to anyone who wants to be successful in this industry. Diamonds are not all the same. The two terms most often used when speaking of diamond tools are diamond grit and bond. Most diamond tools are made of synthetic diamond powder, measured in microns and called grit, and a bonding material, usually metal or resin, or a combination of bonding materials (hybrid tools). They are bonded together through injection molding, hot and cold pressing, electroplating, and vacuum brazing. Speaking of tooling bonds, there are two common problems that you can run into: the tools cut well but their life is too short (premature wear) - this usually happens when using soft bonds that easily open on soft / abrasive floors; or, the tools don't cut well at all and just slide on the floor surface, which is called tool glazing - typically happens when using hard bond tools on hard concrete.

Each grit is designed to refine the scratch pattern, and the rule of thumb is each consecutive grit is to be approximately doubled in size, so it can remove the scratches of the previous step. For example, if you start with 30 grit, the next grit is 50 or 70, then 100 or 120, 200 or 220, 400, 800, etc. Following proper grit sequence is a fundamental principle in concrete processing. Skipping a grit step will put you up against some serious scratched floor challenges. The grits steps are usually divided into three stages — grinding, honing and polishing.

Concrete Grinding - Popular Diamond Tooling for Grinding

Grinding includes the steps from the lowest starting grit (it depends on the floor and application and could be as low as six grit but typically 30 or 50 grit) up to 120 grit. The tools used here are usually metal-bond tools, brazed tools for lippage removal and floor leveling, or pcd tools for coating and glue removal. There are many shapes and designs on the market — round button segments, rectangular segments, single, double or multiple, plugs, etc. But what is more important, especially in the initial cutting steps, is the bond or hardness of the tools. Many contractors have trouble understanding how bonds work relative to different kinds of concrete. Depending on the bonding material, abrasives have different hardness which determines how diamonds are exposed. Hard concrete requires a softer bond to prevent glazing and to allow new diamonds to get easily exposed for maximum cutting. Soft concrete requires a harder bond, so it can last longer (soft bond will cut but it will wear out too fast on soft concrete).

Concrete Honing - Popular Diamond Tooling for Honing

Honing includes the steps between 100 to 400 grit, the tools used in this stage are usually hybrids and/or resins. The hybrids, made of a combination of bonding materials — metals, resins, or ceramics (such as Superabrasive’s Calibra discs or HD discs), are especially useful for removing scratches left by the metal bond tools.

Concrete Polishing - Popular Diamond Tooling for Polishing

Polishing is from 800 grit up to 3,500 grit. The most popular choice for concrete polishing are resin pads/pucks, which are made of poly-phenolic and ester-phenolic. Another thing to consider when choosing tools is there are bonds/tools designed for wet use only, dry use only or wet/dry use. Improper use can cause problems like glazing, sticky residue on the floor, and so on.

“Following all the grits may seem like a lot of steps, but well-trained contractors know that this is crucial for proper floor refinement and achieving a good wear-resistant floor finish,” says Elliott. “It is tempting to buy the cheapest diamonds but concrete grinding and polishing is a very labor-intensive business and lost productivity and time spent redoing a floor is much more costly.”

The point made is that not all diamond tools are created equal, and diamond tools should be always chosen relative to a specific project. Knowing what kind of concrete you are dealing with is important for finding the right combination of bonds and grits which will increase your productivity and ROI, and produce the best floor finish.

Maintenance - Popular Diamond Tooling for Maintenance

With proper maintenance, facility managers can keep their polished floors looking good at a comparatively lower cost than alternative flooring options. Traditional daily maintenance includes mopping and auto scrubbing, using only water or non-reactive cleaning agents when necessary, and cleaning spills and stains promptly. However, in order to maintain their shine and light reflectivity, polished floors require more than that. They require a maintenance program which includes periodic mechanical maintenance with diamond impregnated pads and periodic treatments with chemical cleaners. Furthermore, the maintenance program or schedule has to be designed for a specific floor (not for concrete floors in general), and it will be different from one facility to another, depending on the type of facility, foot traffic, etc. Without proper maintenance schedule in place, the floor shine quickly deteriorates and facility managers end up with a “failed” polished concrete floor. 

Diamond impregnated pads are usually the tool of choice for mechanical maintenance of polished concrete floors. How often to do periodic maintenance is largely determined by the facility foot traffic.

How to estimate my cost and bid for jobs?

Here is an excerpt from a great article from www.forconstructionpros.com  - 12 Tips for Bidding Concrete Polishing Jobs by Rebecca Wasieleski.

"A polished concrete floor project can be a tough job to bid because of the many variables a contractor needs to consider — labor, abrasives, the floor itself, just to name a few ...This list of tips will help you better determine costs before you turn in your bid to a general contractor or home owner.

  • Repairs. Planning for repairs can be one of the most challenging issues a contractor will face when bidding an existing floor project...One thing to remember is sometimes toppings like carpeting and tile were put on a floor because the concrete was bad in the first place. Contractors usually specify spalls per square foot and cover them in the bid. Spall repairs required beyond the allowance in the bid are priced out in an addendum to the bid, as are necessary crack repairs and spalling along joints.
  • Utilities. You need to make sure power in the correct voltage will be available to you on site. If it is not, the power for your equipment will need to come from portable generators.
  • Construction schedule. Find out how much time you have to perform your work and during what times of the day you can do it. If you are working under a tight schedule, or working a job on an existing building still being used for business, you may find yourself confined to do your work nights and weekends. If that is the case, you will need to pay your employees a premium and consider those extra labor costs in your bid.
  • Job schedule. A job schedule, i.e., a plan that lays out when certain trades will be in a building and who they will be working around, is typically not accurate at bid time, so be prepared to be flexible when it comes time for your crew to get on site. What is especially important to pay attention to in that job schedule, however , is mainly two things: floor protection and walls. You may have to arrange for floor protection before and/or after your polishing job. Be sure it is clear in the bid who is responsible for installing floor protection and who will pay for it. You will also need to know if you will be polishing before or after the walls are built. If you get the floor before walls are up, you will have minimal edge work. But if walls are in you will have to consider the extra edge work in your bid.
  • Edges and handwork. This is where all the hard work is. Edges could double your price if you have a lot of small rooms on a project.
  • Samples. Samples and mock-ups take time and resources, and you may want to charge for them. If you get the job, the price the client paid for a mock-up can be deducted out of the contract.
  • Abrasives. There are several factors that will affect your abrasives costs, including hardness of concrete and the number of steps you are required to perform throughout the grinding and polishing process.
  • Cut. Cream, salt and pepper, or aggregate – if the desired cut of the floor is not clear in the specifications, make sure it is before you submit your final numbers on the job. You will see your profit disappear if you bid for a cream cut and have to spend on abrasives to handle an aggregate cut.
  • Joints. Most specifications will require the polisher to do joint work on the floor. While a saw cut control joint might be 1/8-inch wide, a construction joint can be ½ inch wide. Your joint filler material needs will vary depending on the types of joints in your floor. That material isn't free; plan for that amount in your bid. If you find out on the job you are running short, you might have to pay high costs for shipping in extra to the jobsite – costs that will come out of your pocket.
  • Mix design. Find out the mix design of the concrete. It will tell you the psi of the concrete, which is one factor in determining your diamond usage for a project. 
  • Disposal. Take a look at you job and decide if it will be a wet grind or dry grind. You will need to factor into your bid equipment and costs for dust control or slurry disposal."

Specifying a polished floor

This article is from an interview with Jim Cuviello, which was published in 2009 on www.forconstructionpros.com . Jim Cuviello is the owner of Cuviello Concrete - Polished |Stained |Crafted (concrete-medic.com) and the director of the Concrete Processing and Polishing Technical Institute, CPTInstitute.com, located in Stevensville, Md.

When a designer or architect is specifying a processed concrete floor, the first step is to determine the desired finish. Considerations need to be made for the surface cut, clarity of reflection and decorative applications such as coloring, saw cuts, engraving, seeded decorative aggregate, etc. After the desired look has been determined, specifications for completion need to be written. For new concrete the specifications start in "Division 3 - Concrete." Within this section you will find the specifications for mix design, finishing, curing, control joint placement, protection and sometimes the processing process. If the processing process is not listed in Division 3 it will most likely be found in "Division 9 - Finishes." Following are some brief points to take into consideration when specifying a "Polished Concrete System."

Mix Design

Mix design varies from one geographic region to the next as a result of available aggregates and weather conditions. If possible, do not air-entrain; if entrainment is necessary do not exceed 3 percent. Keep fly ash to a minimum, not to exceed 20 percent of the cement weight. Do not use calcium chloride-based accelerators. Use a 3,500 - 5,000 psi at 28 days mix. When exposing aggregate, understand how the aggregates will look when polished and how well that polish will hold up compared to the concrete's finished surface. Final color of dried mix if the floor does not receive stain. Final color of dried mix will affect the overall color of stains.

Finishing

Floor Flatness (FF) above 40 will minimize a wavy appearance in a floor when finished. Mechanically trowel the surface to the point right before burning and do not allow the power trowel to run dry. In areas that receive hand troweling, make sure the concrete has been well consolidated and troweled as tight as possible. If a fine aggregate finish with minimum aggregate has been specified, thoroughly floating and tamping will help bring more cream to the surface. Curing Hardeners/densifiers react with calcium hydroxide to form additional calcium silicate hydrate (CSH). CSH is the material that bonds the cement to the aggregate. If a curing agent has to be used, ensure it is water based and UV dissipative. Remember, the hardener/densifier and stains must be able to penetrate the surface for a successful installation. A cream finish cannot be obtained if a cure and seal or tilt-up wall mold release agent has to be ground off. If possible, water cure to reduce edge and joint curling. Curled edges and joints will have more exposed aggregate then the rest of the floor when the surface is processed. Concrete must be cured for a minimum of 28 days before processing. Control Joint Placement Control joints should be placed so they are not running down the middle of hallways or in highly visible areas

Installation Process

At no time should any consecutive grits be skipped following the starting grit abrasive.
The Installer will drop back one girt resin abrasive from the last metal grit abrasive used. A separation in grit designation size must be a minimum of 50 when transitioning from metal to resin.
The Installer will refine the concrete surface with each grit abrasive to its maximum potential before moving on to the next consecutively finer grit. The Installer must refine the concrete surface further than replacing the scratch pattern from the previous grit abrasive with the next grit abrasive.
Application of a densifier will be dictated by the concrete but will not be applied any later than 200-grit resin unless circumstances present themselves and are approved by the architect. The surface must be free from any random scratch patterns throughout the process and in the final product.
The floor must be cleaned between each grit until any particulate grit larger in size than what the next grit cut will produce has been removed from the floor before continuing to the next progressively finer grit.
All edges must be uniformly cut and processed when compared to the rest of the floor.
Corrections should be made before application of Impregnating Micro Filming Stain Inhibitor.

Protection

  • Vehicles and lifts are not permitted on surface if possible.
  • Do not allow acids to contact surface.
  • Do not place any material onto surface that may cause staining, etching or scratching.
  • For concrete that has been processed without satin or any type of sealer, a guard or impregnator, it can be covered with rosin paper, masonite, drywall and plastic in any combination as long as there is no vapor transmission. If the concrete is still curing make sure all joints are taped.
  • For concrete that has stain, sealer, a guard or impregnator, it is imperative that it be 100 percent cured before being covered with any material that will not allow it to breathe.

Working with the trades

It is important that as soon as a job has been awarded to a general contractor that the GC award the concrete processing to a subcontractor and set up a meeting with the architect, on-site superintendent and concrete processing contractor. If it is new construction the meeting should also include the contractor placing and finishing the concrete, concrete supplier and anyone else who may affect the concrete work.
Currently architects and general contractors have little or no understanding of the processing contractor's requirements for an efficient and successful installation. Processing concrete requires large areas to be clear of debris and free of other trades. It is important to determine when the processing work will be performed so other trades are correctly scheduled. Equipment that runs on electric power often has large power requirements that need to be planed for. On new commercial jobs, temporary power is rarely sufficient. When processing new concrete the concrete supplier must understand the importance of strictly adhering to mix design specifications. The placement contractor needs to realize the concrete he is pouring and finishing is not a subfloor but the final flooring surface. There has to be a clear understanding of how to finish the concrete to get the best possible results from the polishing process.
There are other intricacies the concrete processing contractor understands that the GC will not be aware of. For example, if the building is block construction the thickness of the felt between the block and pour needs to be considered. In addition, to achieve the best possible finish along edges the processing should be performed before millwork, including door jambs. Concrete processing should also be performed before painting since the equipment is run tight along walls. The most desirable time for the processor is before any interior walls have been placed although this is not always possible. A word of caution for processing contractors when pricing work - don't assume you will be given the area before walls are placed. As we are all aware, working around walls and tight areas increases time. If the building is block construction you will have to work in hallways, small rooms and tight areas. Regardless of whether the concrete exists or if it is new, all trades need to be reminded that the concrete will be used as the finished floor and should be treated accordingly. The time has come for every contractor processing concrete to learn their trade beyond simply going through the motions. We must understand the technicalities of what we do and be able to convey these technicalities to all those who affect the outcome of the processed surface. For those who are specifying processed concrete surfaces it is crucial that you understand what you are specifying. Will your and the customer's expectations be met? General contractors must listen and be willing to work with the concrete processor's needs for an efficient and successful installation.