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How to prepare a concrete floor

installer preparing floor surface

Preparing a concrete floor can vary hugely in terms of time and technique. The importance, type and degree of preparation required before painting, depends on the type and condition of concrete, the exposure, and the coating system to be applied. The concrete should be clean, dry and free of dust, dirt, oil, surface matter and form release build-up.

When using any of the equipment or chemical solutions recommended below, be sure to follow all manufacturer’s instructions and follow any recommended safety procedures.

Hand Tool / Broom / Vacuum Cleaning

The first method of preparation is the removal of all surface dust, dirt and any other loose/friable material using either a broom or vacuum cleaner. These can be complemented with a sander or wire brush to remove loose matter from the surface and/or to abrade the existing surface to provide a ‘key’ for any subsequent coating.

Chemical Cleaning

An alternative, to the mechanical methods of the preparation of concrete floors for epoxy coatings application, can be accomplished by using chemical cleaning methods:

Acid Etching
Etching is a very low-cost chemical method commonly used to treat concrete floors to remove laitance and provide a profile. The objective of acid etching is to dissolve the weak surface layer known as laitance and open the pores to allow penetration of the sealer coat. Acid Etching products are a concentrated Hydrochloric Acid and should be diluted with water. The volume dilution ratio can range from 1 part acid to 3 parts water to as weak as 1 part acid to 10 parts water depending upon the floor being treated.The surface is pre-dampened and the diluted acid applied uniformly over an appropriate area. The approximate spreading rate is normally around 10sq.m per litre of acid mixture. The acid should remain on the surface for two to three minutes of bubbling reaction. After application of the acid, scrub the surface with a stiff bristle pavement, scrubbing broom or a rotary power scrubber will facilitate the etching process. The vigorous formation of bubbles indicates proper etching and must be obtained. The absence of bubbles or a weak reaction indicates the presence of a curing compound membrane or a surface hardener on the concrete. Once etching is completed, thorough rinsing with fresh water must be done before the surface dries – in order to avoid the formation of salts on the surface. Once formed, these salts are difficult to remove. Any residual acidity must be neutralised with an alkaline cleaner followed by thorough rinsing with fresh water.
A properly etched concrete surface will be hard but porous and will have a profile similar to that of fine sandpaper. Water will penetrate easily and will hot bead up on the surface. In many cases, more than one etching operation is required to obtain a satisfactory result. The etching solution should never be more concentrated than 1 part acid to 3 parts water. If satisfactory results are not obtained with this concentration, repeat the etching procedure. If the surface is rougher than fine sandpaper after one etching, more dilute acid solutions (dilution up to 1 part acid to 10 parts water) should be used. In addition to muriatic acid, proprietary etchants, which contain phosphoric acid and concentrated cleaners, are available and may also be used.As an alternative to etching with hydrochloric acid, the use of phosphoric acid (which is non-volatile) should be considered in sensitive situations.Please note that Acid Etching will not be effective over release agents, most curing membranes, or most surface hardeners. Should you wish to remove greases, oils, or other types of contaminants, these can be treated with a powerful degreaser prior to etching procedure.IMPORTANT SAFETY INFORMATION: Please further note, that both hydrochloric and phosphoric acids cause burns to skin and eyes, and the inhalation of acid fumes may be harmful.

Solvent Cleaning
A Solvent Cleaner is a unique blend of fast drying solvents. Effectively cutting through rubber, grease, oil and stubborn marks this unique cleaner will dry extremely fast and be ready for any repair or coating almost immediately. However, please be aware that this will produce a strong odour and will not be suitable for food or sensitive environment. In enclosed environments, correct breathing apparatus should be used.

Degreasing
The removal of any grease, oils and fats from floor and wall surfaces is imperative, prior to applying paint or other coatings.   Polycote Degrease IT is a powerful multi-purpose cleaner and degreaser, containing phosphate, alkali builders and solvents in a highly alkaline detergent composite.Normally diluted with water at a ratio between 1:4 for floors and 1:40 for machinery, Degrease IT may also be used undiluted for removing severe grease contamination. Spray or pour and brush the chemical onto the surface to be cleaned and allow to penetrate for at least 5 minutes. The surface should then be thoroughly scrubbed to lift the grease or oil from the surface. Once done, this should then be thoroughly rinsed away. An Aquavac is an excellent way of removing the waste. Better still, is the use of a Scrubber Drier which will not only lift the contamination from the surface due to the heavy scrubbing motion but will also suck off the resultant liquid into a built-in waste tank leaving not only a well-cleaned surface but also one that is pretty much dry. As mentioned previously, it is important to realise concrete is like a sponge – it is full of air holes. Pour a bucket of water onto any unsealed concrete floor and you will watch almost the entire amount simply disappear. The water will rise and evaporate over the following few days until the concrete reverts to a completely dry state. However, when oil or some other form of contamination has penetrated the concrete, this will never evaporate. As the oil has penetrated into the concrete, it must be realised that a chemical clean will only wash the top surface. The oil remaining within the slab will simply rise to the freshly cleaned surface and the floor will appear to be as dirty as it was immediately prior to cleaning. Before the coating of the floor, priming of the floor should be completed as soon as possible after the completion of the cleaning. A very good primer can bind up to 15% oil into itself and its unique ability to adhere to previously contaminated floors is almost unparalleled.

Mechanical Cleaning

The preparation of concrete using certain mechanical methods has the advantage of speed. If the more rigorous methods such as blasting or scarifying are attempted by insufficiently trained operators, however, removal of too much of the surface can easily result in exposed aggregate and an overly rough and porous surface. It must be realised that improperly performed mechanical preparation can severely damage a concrete floor.

Power grinding, sanding or scraping can be used to open holes and voids and to remove curing membranes, some hardeners, loose matter and laitance from the surface of floor slabs. These methods can be used in place of blasting but are considerably slower and less effective.

Shotblasting This method of industrial floor preparation is widely regarded as the most professional and most effective surface preparation method for concrete is a light blast with a Vacuum Assisted Shot blaster. The objective is the same as acid etching. The blast removes all form release agents, weak concrete, laitance, dirt and contamination. Being connected to one of our highly powerful industrial vacuums assures that at least 95% of the dust is contained.

Scarifying / Scabbling When inspection and testing procedures indicate concrete floors must be chipped down to sound concrete Scarifiers and Scabblers may be used to remove the top layer of concrete to expose a fresh, clean surface. This technique is practical only for floors. Important; dust protection is required when used in the presence of machinery, food or close traffic. We have a full team of qualified operatives ready to complete this work as necessary. However, the equipment can be either purchased or rented should you wish to complete the work yourselves. Please be free to ask.

Hand Held / High-Speed Diamond Grinders Far more than just a ‘sander’, our Diamond Grinders are powerful enough for almost any demanding industrial requirement. They are used for many and varied applications, from the ‘keying’ of existing surfaces, removal of existing paint and weak laitance, to the smoothing out of uneven surfaces, we have a grinder that will be ideal for your application. On the contrary, we are often asked for the complete whereby we are asked to actually roughen the surface to achieve higher levels of slip resistance.Diamond grinding can smooth out floors to a laser level finish, removing minor pits and divots, high spots and roughness on concrete floors. Should two slabs of concrete be poorly laid to a different height, the grinder is used to smooth out the transition from one slab to the other. A huge benefit of the system is that all machines, ranging from simple hand held grinders to the biggest ride-on machines can all be connected to industrial dust recovery units. This, in turn, means that we can achieve a 95% dust free operation.With grinders that have pressure controlled rubber mounted non-planetary grinding heads and specially designed diamonds, you are able to grind and/or polish without scouring the concrete, even on cracks and expansion joints. The specialist disc, embedded with a coarse diamond grit can easily prepare, clean and abrade existing coatings for re-coat. This process will remove thin layer coatings and weak toppings and provide a textured finish suitable for two coatings to bond together. Should an existing coating be already down that is fundamentally adhering very well to the surface but one that simply needs rejuvenating, the keying off this existing surface in order to accept a further coat can also be easily achieved.In comparison to shot blasting, diamond grinding is relatively is slow and intensive. However, the finish left can be far smoother. In some cases, we are asked to actually polish the surface to a super smooth finish.Please do note however that in the wrong hands, diamond grinders can leave swirl marks in the slab should the operative be untrained or overly aggressive.

FURTHER TECHNICAL HELP REQUIRED?

Should you still have been unsure as to the best solution for your needs, please ring our technical helpline now on 01234 846400 and speak to a fully qualified team ready to give practical advice and help assist you as much as possible.

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