How to achieve different levels of sheen on a polished floors and a better understanding of Polished Concrete:
At a level 3 polish, your concrete floors will really begin to shine and clearly reflect side and overhead lighting.
Depending on the diamond grit you use to polish a concrete floor, you can achieve different ranges of polish and different levels of sheen, from matte to a glassy mirror-like finish. These ranges are typically categorized in levels ranging from 1 through 4. For coarse grinding, you’ll generally start out using diamonds embedded in a metal matrix. As you begin to polish the floor in successive passes, you’ll typically switch to finer diamond abrasives bonded in a plastic or resinous matrix to achieve higher degrees of shine. Here are the four levels of polishing and the degree of shine you can expect to achieve at each level. (Source: Bob Harris’ Guide to Polished Concrete)
Level 1 polish A level 1 polish usually can be obtained by stopping at the 100-grit resin bond. When you look directly down at the floor, it will appear somewhat hazy with little if any clarity or reflection.
Level 2 polish A level 2 polish is obtained by stopping at the 400-grit resin bond, producing a low-sheen finish. When you look directly down at the finished floor and at a distance of roughly 100 feet, you can start to see a slight overhead reflection. This grit level produces a low-luster matte finish.
Level 3 polish A level 3 polish is achieved by going up to an 800-grit diamond abrasive. The surface will have a much higher sheen than that of level 2 finish, and you’ll start to see good light reflectivity. At a distance of 10m – 15m, the floor will clearly reflect side and overhead lighting.
Level 4 polish This level of polish produces a high degree of shine, so that when standing directly over the surface, you can see your reflection with total clarity. Also, the floor appears to be wet when viewed from different vantage points. A level 4 polish is obtained by going up to a 3,000-grit resin-bond diamond or by burnishing the floor with a high-speed burnisher outfitted with specialty buffing pads.
Measuring the gloss level Once you have completed the entire polishing process, you’ll be left with a beautiful, shiny surface. But how do you accurately assess the degree of shine, other than by simply visually inspecting the amount of light reflectivity or clarity of the polished surface? Today, specifications for polished concrete are now including specified gloss readings, determined using gloss meters (see table). Gloss values express the degree of reflection when light hits the concrete floor surface, and range from 20 to 30 (low gloss) to 70 to 80 (high gloss). For example, a gloss value around 30 will generally produce a low-satin sheen while a value of 80 will produce a very high shine, especially after high-speed burnishing.
Gloss Level Table
Level 1
Grit – 100
Sheen Level – Dull or matte look
Gloss Reading – N/A
Appearance – Floor has little if any reflectivity.
Level 2
Grit – 400
Sheen Level – Low sheen
Gloss Reading – 40 – 50
Appearance – From a distance, floor will start to reflect images from the side. Floor has a whitish or cloudy appearance.
Level 3
Grit – 800
Sheen Level – Shiny look that is slightly cloudy
Gloss Reading – 50 – 60
Appearance – At a distance of 10m to 15 m, the floor reflects from side to side. Floor starts to shine, but has a slightly fuzzy appearance.
Level 4
Grit – 1,500 – 3,000
Sheen Level – High sheen with clarity
Gloss Reading – 60 – 80
Appearance – Looking straight down on the floor, it clearly reflects overhead and side lighting. The floor is very shiny and looks wet from a distance.
It needs to be noted that different aggregates offer varying grades of shine. The harder the aggregates are, the better level of shine can be achieved, versus the softer aggregates. (Refer to Moh’s Hardness that is a measure the ‘hardness of the materials’)
Different materials and aggregates can offer different results. The binder content of concrete, is of course cement. The higher the strength of a mix, the better the result and the better the wear and abrasion resistance the surface will offer. The optimum strength we recommend is a 35Mpa. (One also needs to be careful of concrete mixes with a high ‘extender content’ (eg fly ash / slagment). Pump mixes will reduce the uniformity of
the aggregate dispersion. We generally recommend the addition of polypropylene micro fibres, which helps to make a more ‘ homogenous mix’. The placing of the concrete needs to be placed by a team that is experienced and understands what the expectations and requirements of a polished concrete is. It is essential that the concrete vibrated with a mechanical vibrator and the surface is pulled/ struck off using a vibrating beam. The surface is to power floated smooth (not burnished) and ensure that all the pin holes are closed.
Please find below CHCSA approach for the installation of a diamond polished concrete floor.
Planning
1. Ensure that the concrete is designed at the most suitable thickness and the right strength.
2. Concrete overlays (topping) can be done on top of concrete. We generally recommend that this be a minimum thickness of 50mm.
3. Joints need to be designed in the right strategic places. One should always try to reduce the amount of Construction Joints and put them in strategic places. (Saw cuts generally offer far neater finish)
4. We recommend that joints should not exceed more than 30 x’s the concrete thickness (eg, if concrete is 100mm thick x 30 = 3000mm x 3000mm)
5. The aspect ratio also needs to be considered (length : width). This should not exceed more than 25%
6. Joints should planned that they preferably intersect with corners.
7. Corners are always introduce a risk of cracking. Shear bars / crack prevention bars should be installed in the correct position. (We have a document that can advise further on this)
8. All walls and columns should be properly isolated with a ‘closed cell expanded polyethylene’ (typically Jointex)
Concrete quality
1. Ensure the best mix design is used for the concrete. Concrete must be a minimum of 30mpa.(We would prefer to see a 35Mpa)
2. We generally recommend to include a polypropylene micro fibre at 600g per m3
3. Maximize the stone content
4. Minimize the water demand
5. Use mixes with the best possible sand and sand gradings be used.
6. Ensure the correct cement is used with the correct volume of cement replacements (Mixes with high dosages of extenders, such as Flyash and Slagment, can reduce surface abrasion resistance)
7. Ensure supply consistency and correct slumps
Concrete placing
1. Make sure correct level control is in place.
2. Make sure concrete will be protected from the elements (sun / wind)
3. Use the correct equipment to place, consolidate, strike off and level the concrete.
4. Prevent rapid loss of moisture from the surface immediately after placing and continue doing so until power floating commence.
Power floating
1. Be careful of starting with the power floating to early
2. Use pan fitted power floats for the initial power floating and continue using this until the surface is properly consolidated.
3. Use blade fitted power floats to make the surface dense
4. Start curing procedure as soon as you can walk on the surface without leaving any marks on the surface
Diamond Polishing
1. Grind surface to expose aggregate: 3-4 steps, metal bonded tools
2. Do all repairs if required and grout surface
3. Remove grout with metal tool
4. Apply liquid densifier
5. Polish surface – 5 steps Resin bonded tools
6. Apply suitable liquid densifier
7. Buff surface.
8. There are additional sealers which can be applied to the surface, which can further enhance the floor finish as well as help reduce the risk of staining. Certain sealers are available which reduce the risk if slipping.
Should you require further information, please contact myself for experienced advice. Chris Howes chris@chrishowes.co.za
We look forward to being of further positive and constructive support!