Concrete Finishing Techniques
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Almost every fairy tale ends with the phrase “they lived happily ever after.” Usually after these words, we no longer track the further fate of the heroes of history. For floors, the phrase, “they served happily ever after” ends the stage of concrete finishing. And the work begins!
Concrete Finish in the building environment is considered one of the most critical stages in the installation of floors.
Exterior concrete finishes is necessary to improve the quality of coatings and increase the service life of structures.
Heat and moisture treatment of concrete
Heat and moisture treatment of concrete is a technological process that accelerates its hardening, thus achieving design strength. The technology is implemented in special chambers at atmospheric pressure or in autoclaves, in thermoforms, cassettes. The heat carrier is hot water, water vapor or hot air with high humidity.
How to finish concrete? General cycle of heat and moisture treatment:
- Period of preliminary aging.
- Period of temperature rise – until reaching the highest level.
- Isothermal heating.
- Cooling period.
Heat and humidity capital concrete finishing leads to an additional increase in concrete strength up to 50-100 MPa
The rate of the temperature rises and the exposure time depends on the stiffness of the concrete mixture, the type of additives and the activity of the cement used. For example, quick hardening cements can increase the rate of temperature rise and reduce the exposure time. Most often, concrete is processed in autoclaves (special sealed chambers).
Full autoclave cycle:
- Steam supply and gradual heating to 100 degrees.
- Increasing steam pressure and increasing temperature to maximum values (0.8-1.6 MPa, 175-203 degrees).
- Keeping products.
- Decrease in temperature and pressure.
- Cooling of concrete to ambient temperature.
In winter concreting, the source of heat more often is the energy of electric current. Concrete processing can be implemented by passing current through reinforcement and metal molds.
In the summer period, it is more difficult to obtain high-quality concrete. Due to high temperatures and low humidity, water evaporates intensively from the surface, so it needs to be protected with film materials. When preparing and laying the working solution, it is required to accelerate the hardening process with the help of accelerator additives or quick-hardening cements.
Surface preparation and cleaning is a labor-intensive and complicated technological operation, which is performed almost always before repair and application of intermediate, finishing layers. Concrete must be strong in tension, compression, shear, bending, have a certain moisture content, without depressions, protrusions, cracks, shells and foreign inclusions.
The surface should be homogeneous, without mold, dust, dirt or oils. This is the only way to achieve high quality work when applying protective, moisture, waterproofing, decorative coatings.
Best way to finish concrete – Processing Tasks:
- Removal of easily exfoliating, loose layers.
- Elimination of shells and cracks.
- Removal of all layers that prevent adhesion.
- Removal of layers affected by chlorides to the depth where their content is unacceptable.
- Cleaning fittings.
Criteria for assessing the condition of the base:
- Concrete surface cleanliness – there should be no foreign components on the base that reduce adhesion to subsequent layers. If you wipe the concrete with a black rag, there should be no residue on it.
- Humidity control – determine the need for wetting or drying concrete. For organic solutions, humidity should be 5%, for mineral solutions – not higher than 8%.
- Temperature control – is carried out in order to comply with the coating laying regime.
the presence of cement milk on the surface – if you scrape the base with a knife and dust forms, it must be cleaned, otherwise adhesion to the following layers will be insufficient.
- Homogeneity – if there are irregularities of more than 3 mm on the surface, they are removed or smoothed by leveling and repairing compounds.
- Pollution of concrete – it can be chlorides, nitrates, sulfates, fungi, etc.
Concrete contaminants are removed locally or together with salted concrete.
This is a universal method of exposure, which is used almost everywhere.
Work is carried out using:
- Metal brushes
- Milling cutters
- Grinding wheels
- Diamond cups
- Needle hammers
- High-pressure apparatuses
- Construction vacuum cleaners
- Rake finish concrete
The equipment used differs in performance and power. The implementation of methods that lead to polishing is unacceptable where surface roughness is needed. In addition, mechanical Concrete Finish can cause microcracks. Well-prepared concrete should be smooth, rough and without depressions and protrusions.
The main criterion for choosing materials intended for processing specific structures is the nature of the operating conditions.
Depending on the conditions, paints and varnishes are divided into waterproof, weatherproof, resistant to special environments (UV, high temperature, oil, chemistry, bioactive substances).
It also takes into account what type of finishing is done: machine or hand finishing concrete.
However, such an assessment is not enough, so other technical and economic factors should be taken into account:
- Compatibility with other protective equipment used (say, cathodic protection),
- Suitability for restoration and repair,
- Application technology,
- Fire safety and sanitation requirements, and
It would seem that if we are talking about an essentially uncomplicated operation of leveling concrete poured floors, the brand of equipment used does not really matter. However, practice shows that it is in this part that the technology for the production of industrial floors makes great demands.
Leveling is a crucial step in creating concrete floors
Concrete floors are widely used today in civil and industrial construction. The most important part of the technology is leveling: after the concrete screed is poured and leveled, before it completely dries, it is necessary to remove the smallest bumps and irregularities present on the surface. And here the “helicopters” come to the aid of the builders with trowels, also called smoothing, concrete machines. The use of “helicopters” is a prerequisite for obtaining a perfectly smooth and even floor surface.
How to trowel finish concrete? Concrete Finish using a trowel is produced in two stages. At the first stage, the roughing disk performs roughing – removing large flows and significant defects. The readiness of the poured concrete for leveling is determined by the print of the operator’s footwear – the trace depth is not more than 1-2 mm. At the next stage, the disk is replaced with nozzle blades, and with their help finishing, the concrete surface of the floor is done to the desired degree of evenness. When choosing the size of the blades, the volume of work performed is taken into account. The working area depends on the diameter of the rotor – from 600 to 1200 mm or more. Moreover, the larger the area of the blades, the more wet concrete can begin to cover them. The blades are available in three versions. These are floating, usually used at the initial stage of smoothing concrete and able to replace grout disks. Combined blades most effectively level the floors. The grouting time of the surface of fresh concrete with a disk can be reduced if, after a short period of leveling with a grout disk, the disk is replaced with floating and combined blades to continue leveling.
Finishing blades are used for the final polishing of the concrete surface. In most trowels, the angle of inclination of the blades with respect to the work surface can be adjusted. For various stages of smoothing and concrete condition, an experienced operator selects the rotation speed and one or another position of the blades, thereby increasing productivity and quality of work.
There are one-rotor and two-rotor trowels for concrete finish options. In single rotors, a group of so-called hemmers is distinguished – small, compact units with a rotating outer protective ring that protects the trowel blades or the trowel from contact with an external barrier. These machines do an excellent job of processing sections of the floor near walls and columns; for maneuverability, they use rotors with a diameter of not more than 600-750 mm. Single-rotor machines with a blade or disk diameter of 900, 1200 mm are used when leveling small areas of concrete pavement in halls, production halls, etc.
For operation in enclosed spaces, electric hemmers are used.
Single-rotor machines are controlled by the operator, and management, as a rule, does not cause problems even for an unprepared employee. The operator must have a solid support surface under his feet and stand behind the machine in the center of the handle. By smoothly increasing the speed with the regulator on the handle, it sets the speed of rotation of the disk or blades required by the technology, and then, pressing the handle down, can turn the machine on to the right, and by lifting the handle up, set the machine to the left motion vector. Similarly, by turning the control knob slightly to the right or left, the operator forces the machine to move forward or backward.
A two-rotary trowel moves independently on the surface to be machined, and control is carried out by an operator located on a seat in the upper part of the machine. The control of the speed and direction of movement of the machine on the surface, as well as the angle of inclination of the blades and the speed of their rotation, is quite simple, using joysticks or levers, depending on the model and manufacturer of the machine. Two-rotor ones are divided into two main types: with overlapping trajectories of the blades on different rotors (overlapping) and without it (double-disk or non-overlapping).
Machines are used for leveling concrete screeds of significant area. An example is an industrial garage concrete finish. They work with different diameters of discs and blades — 600, 900 and 1200 mm—and are designated as 2×750, 2×1200 or 2×1600 mm.
The task of all trowels is to level the surface of the concrete floor, eliminate bumps and air cavities, prepare the surface for either coating, or for the grinding operation with a mosaic grinder.
Concrete Finish – Concrete Floor Grinding
Concrete grinding is a method of treating a concrete surface, in which the old coating is removed, damaged areas are restored and the base is leveled for further application of protective materials. Such work significantly increases the service life of the concrete floor and makes it perfectly smooth and beautiful.
Grinding of a concrete surface is carried out in rooms for various purposes, as well as in open areas. Processed concrete finishing can be seen in various places:
- large shopping and entertainment centers and supermarkets.
- medical institutions.
- water parks and centers for sports.
- cinemas, museums, restaurants and other recreational facilities.
- schools, institutes and other educational institutions.
- suburban areas.
- garages, warehouses, outbuildings.
- lobbies and corridors in residential buildings, etc.
- After grinding, the concrete floors look aesthetically pleasing and attractive, while improving their technical characteristics:
strength and reliability are increased.
- the term of operation increases.
- the coating becomes resistant to moisture and chemical influences.
- the surface is less worn and cracked.
- floor care becomes easier.
Also, grinding concrete allows you to restore the old surface with existing defects by removing the top layer, repairing cracks, removing bumps and final polishing. As a result, the floors look like new.
What types of concrete finish to choose: dry or wet?
The type of grinding of the concrete floor, whether dry or wet, will depend on the type of foundation, but the equipment used to perform these operations is the same. This is due primarily to the fact that a tool of this type is required to cope with both concrete surfaces, for grinding which the dry method is preferable, and stone coatings, which are polished using moisture.
Why is it necessary for a concrete floor to dry sand? Is it because it takes time much more wet? The answer is obvious: while dry polishing, there is a lot of dust, but it does not so impair visibility as it does with the wet method, with its cement slurry. Consequently, visibility in the performance of work will be better, and the employee can easily see his mistakes.
To remove dust from the construction site, industrial vacuum cleaners are used, which are much cheaper than their water counterparts. Vacuum cleaners are also used to utilize and collect liquid sludge from cement, which is removed from the concrete coating during wet grinding.
Today, two types of apparatuses are presented: special-purpose masks and ordinary grinders, for use at home.
Professional-grade equipment is characterized by excellent quality and the presence of the planetary mechanism of a special system, which is a large disk with satellites equipped on it, moving unidirectionally. Satellites, with diamond nozzles attached to them, move in the opposite direction. This complexity of the diamond movement system creates a perfectly smooth and even concrete surface.
Planet grinding professional grinder for Concrete Finish
In addition to the planetary system of moving nozzles and discs, professional grinding machines have speed and water flow control. It has adjustments, the possibility of collecting sludge and dust from a concrete surface and an impressive weight (the more the weight of the machine, the higher the grinding efficiency is higher). Of course, such equipment is perfectly managed with its duties and only its value can scare the average man. A number of models are comparable in price to a good car from an American manufacturer – about several hundred thousand dollars. Fortunately, for ordinary users, there are options available at a very reasonable price, although it is also with “teeth.”
A grinding machine for home use from a professional is compact in size and has a single diamond blade.
The initial stage of grinding is the removal of irregularities on a fresh concrete surface, as well as the removal of old coatings by shot blasting, using a special tool for grinding or milling. During this operation, general concrete finishers advise using diamond disks with a grain size of 25-30. A disk of this type can remove “cement milk” from the concrete coating and it is also able to expose the filler (crushed stone or crumbs). When only the surface layer needs to be polished, in particular, a brand-new concrete screed, grinding can begin with a forty-grit disk.
The task of the second stage is to eliminate all kinds of defects: cracks, expansion and shrink joints, potholes, etc. You can fix them with an epoxy mastic that perfectly fills any bumps. It should be smeared so that the grinding heads of the machine freely pass through defects without clinging to them.
Concrete surfaces “soft” lend themselves to grinding easier than “hard” ones, and at the end of polishing, they look great — only diamond nozzles will have to spend much more on the job.
How to sand finish concrete? Stage Three – in fact, grinding, which can be divided into several levels.
Grinding coarse concrete floor with diamond cups with grit size 40.
Floor hardening. The special composition, as a result of the reaction with calcium hydroxide, which is part of the concrete composition, forms an astringent mineral substance that closes the pores in the concrete, thereby making it much more resistant to moisture and stronger.
The process of grinding with diamond discs with grit from 400 and higher creates a durable concrete layer that can withstand not only the walking of a large number of people, but also the weight of the forklift trucks. This stage can be final, since the concrete surface will already be strong enough, maintenance-free and reliable.
Polishing discs with grit size from 1500 to 3000. The final step is to achieve a perfect smooth surface and an impressive gloss.
The preliminary stage, that is, the assessment work on the inspection of the old concrete screed, should be accompanied by the following points:
If sealants or some other coatings were previously applied to the concrete surface, it is necessary to find out how difficult it will be to get rid of them. Deep scratches or grooves remaining after removing the old coatings will have to be removed by long grinding. Therefore, not only time, but also money will be spent. If potholes, knolls and pits are found on concrete, the volume of used diamond cups also increases.
Voltage is an important element in evaluating an object, because grinding machines require stable current strength and equally stable voltage for normal operation of the machine.
Concrete Finish – the task of grinding concrete floors
The task of grinding concrete floors is to remove small defects, bumps, ripples and open pores. But the wave differences with its help cannot be eliminated, since the machine repeats all the bends of the surface during movement. This problem can only be eliminated by the method of complete re-filling of the upper layer. Therefore, you should not treat the filling just as if, in the hope of the help of the grinder, but do it right away with good quality.
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