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How to Deal with Concrete Surface Impurity before Floor

Date: 2017-01-02
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The quality of the concrete base combined with the floor coating or repairing adhesive material depends to a great extent on the cleanliness of the concrete surface and the surface cleaning and preparation work. The ability to resist water, antifreeze salts, sea salt (liquid or gaseous), oxygen, carbon dioxide and other corrosive contaminants is usually taken into account by the needs of the user, the outer structure as a whole. In addition, the impact of the repair work on the environment (such as noise, dust, etc.), the overall performance of the structure, the durability of the restoration material, the impact on human health and its safety should also be considered.

1, the common surface impurities

 Surface impurities are liquids or solids that can potentially affect the adhesion, conservation, or associated use problems of the coating material with the concrete. Surface impurities must be completely removed before repairing and pasting work, so as not to affect the adhesion of coating materials and concrete base properties, some common impurities are as follows:

1.1 conservation solution

Some of the curing solution may be compatible with the coating material, but should be thoroughly removed with adverse reactions.

 1.2 Dust

Industrial pollution or dust caused by the surrounding construction will pollute the concrete surface, should be used vacuum clean equipment or clean oil-free compressed air blown away.

1.3 Salting out

Salt precipitation in concrete material and water will migrate to the concrete surface, water evaporation, the crystal remained in the concrete surface. Water and dissolved salts migrate from the high temperature side to the low side.

 1.4 cement floating slurry

Aggregate segregation The resulting cement slurry forms a weak layer on the outer surface of the concrete. Usually due to improper water-cement ratio or in the construction of the lower temperature of the concrete continued exposure to the air or the opposite layer of plastering over-pressure and cement particles were taken to the concrete surface. The thickness of the floating slurry layer is 1.6-3.2mm.

 1.5 Release agent

It is a release material used to facilitate the removal of molds, often remaining on the concrete surface.

 1.6 grease, tar pitch and resin

These substances penetrate into the concrete to make it difficult to clean up and penetrate into the coating material to form stains. Tar pitch, resin, and asphalt-based materials have the same effect as grease. In addition, the hydraulic fluid such as brake fluid, transmission fluid and so has a strong penetration, need to use some special methods to clear.

 

2, the common surface defects and internal impurities

 2.1 Burr

As the edge of the burr coating surface tension pull back, resulting in glitches on the coating is not flat and the thickness of the lack of application of grinding tools to polish the surface of concrete, and then wipe the surface layer of floating dust with cotton yarn, and finally with a vacuum cleaner or strong air cleaning Machine cleaning.

 2.2 "Eggshell"

This is a thin, sometimes translucent-like cement slurry film. When the residual moisture in the membrane after the formation of pores in the concrete surface and honeycomb. This layer is very easy to break, exposing the hole under it. The "shell" area should be positioned, to be cleaned up, the hole should be formed to repair, so that with the surrounding concrete as smooth.

 2.3 tie hole

For the removal of the template after the pull rod left in the concrete surface of the small holes should be cleaned and repair the formation.

 2.4 Plastering

Some handmade plaster can cover small defects in the concrete surface and fill some pores, but its adhesion is very low, so it must be removed before the coating work.

 2.5 Internal impurities

Concrete itself may contain chemical impurities and hidden mechanical defects, such as chloride, sulfate and nitrate salts can produce swelling caused by concrete cracking. Chloride will lead to corrosion of steel, the surface of the concrete will be carbonized.

 

3, cleaning methods

 

Should make concrete exposed clean, solid surface, should try to avoid hammering and rough chisel, so as not to concrete surface in the range of about 9mm to form split area.

 3.1 Chemical Cleaning

Typically, hot water-soluble trisodium phosphate (TSP) or some detergents and emulsifiers are used to remove surface contaminants. In order to avoid chemical cleaning materials remain in the grass-roots surface, after the need for clean water for washing.

 3.2 Hydrocarbon solvents

Methyl ethyl ketone (MEK) and xylene should not be used as cleaning agents, although they can dissolve impurities, but will impurity diffusion to a larger surface area, while deeper into the concrete, should follow the recommendations of manufacturers Selectively used.

 3.3 Steam cleaning

This is an effective method to remove water-soluble impurities on the concrete surface. Steam cleaning using a large number of wet or dry steam, high density and a certain rate of direct action on the concrete surface to soften and remove these impurities. Cleaners, degreasers and other chemicals are sometimes added to the water to improve cleaning efficiency. Steam cleaning has limitations and can only be used to clean the surface of the concrete rather than impurities in the pores.

 3.4 Chemical stripping

Chemical stripping is a wet treatment of surface clean-up, usually with methylene chloride and a hydroxide-containing base to soften or dissolve the coagulated coating for each subsequent mechanical removal. Additional cleaning and surface preparation is required to aid chemical stripping prior to coating work. In addition, the high pH of the coating stripping agent should always be placed in the final selection. The method is generally limited to small areas where more efficient preparatory work can not be done.

 3.5 Shot blasting treatment

Centrifugal shot blasting is a highly efficient, clean and dust-free method for hard surfaces. This method is most commonly used. Shotblast processing equipment for the internal rotation of a high-speed impeller, abrasive, dust and impurities are cleared to the debris recovery machine, after cleaning up the steel shot can be recycled. Shot peened concrete surface clean and hard, there are relatively uniform texture. This method is particularly useful on barrier-free horizontal surfaces.

 

Usually a shot blasting treatment will make the concrete surface cut to 3mm. If only the treatment of floating layer or the need to deal with the surface layer thickness <890um, you need to use fine steel shot abrasive. The use of fine steel pills or high-speed moving gears produces very light scoring on the concrete surface to make it easier to bond the coating and paste layer to the concrete surface. If there are multiple layers of thin adhesive layer, use a beveled steel grit. Grit without puncture the piercing layer, will not adversely affect the grassroots, but the use of angle grit will increase the wear of the device. Composed of about 60% steel shot and 40% abrasive, it can reduce the wear in the same working environment compared with 100% bevel abrasive, but should pay attention to prevent the steel balls or abrasives from being mixed with grease, impurities Mixed together, and to avoid water. Shot peening is not very effective when cleaning elastomeric materials.

 3.6 Blasting cleaning method

Blast cleaning is performed by impacting the concrete surface with a fine abrasive that is driven by clean compressed air for high speed movement. These abrasives are usually composed of hard, bevelled minerals with well-chosen particle sizes. The sand blasting treated concrete surface texture uniform, hard and no impurities. Concrete surface hardness determines the effect of surface treatment by sandblasting.

 

The same tools, the same air pressure, hose length and nozzle size and abrasives should be used in the test area, and the treatment time, effectiveness, and surface coarseness of the coagulation surface should be evaluated. Generally larger size abrasive used in concrete rather than steel products. Sand abrasives with a particle size of 1600-2000um are often recommended for handling difficult surfaces. If only the superficial slurry of the concrete is to be removed, a sand abrasive having a diameter of between 350 and 840 um is sufficient. Mineral abrasive should have a sharp bevel and the hardness of at least Mohs hardness of 6.5, otherwise the mineral is too soft and ineffective. Too soft abrasive broken rate, in the impact of concrete surface can easily lead to excessive dust, reduce work efficiency. Should avoid the use of free silica sand abrasive, so as not to cause the occurrence of the operator silicosis. The need to suppress dust can be used wet sandblasting method. The rubber elastic material, sandblasting effect is not very satisfactory.

 3.7 Vacuum cleaning / air purging

 The use of vacuum and oil-free compressed air pressure gas blowing, can remove the concrete surface of the dust, debris. When the need to control the scattering of dust when the preferred vacuum method.

 3.8 Acid etching

Acid corrosion can make the concrete surface roughening, but can not remove the floating layer or other loose material. A 10% hydrochloric acid solution is usually used. Concrete should be pre-wet, all grease, paint, putty, resin, tar and other impurities should be removed in advance to ensure uniform surface corrosion. Some products contain surfactants to remove grease from the concrete surface. Tar, resin and other thick and soft impurities can be scraped or frozen and then strong scraping. Thoroughly remove impurities, every 5 - 7m, the concrete surface spray 4. 5L acid solution and maintain 2 - 3min, and then immediately rinse with water to prevent the formation of salt. Repeat this process until the concrete surface is as rough as a medium sandpaper. It is recommended to use the minimum pressure of 14MIPa water rinse, with 150 nozzles can achieve better results. Pressure water can rinse the surface of the concrete particles and ensure that wash away the acid weak layer and the surface corrosion layer, in order to improve the adhesive layer and the substrate adhesion.

 

Construction sometimes does not have the conditions of pressure water, a neutralizer can be dispersed into the water to neutralize the acid. With 4% ammonia in the volume ratio of 1:21 mixed concrete surface after washing effect is better. Neutral solution in the concrete surface infiltration of 5min after rinsing the surface with water. If the drainage inconvenience, can be used to vacuum to stay stranded water and then rinse with water. This process was repeated until there was no impurity particles in the rinsed water. After washing, the concrete surface should be tested with litmus or pH paper to ensure that it has been neutralized. Acid etching is used when no other method is feasible.


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