The requirements for surface treatments of concrete floors naturally vary within a wide range – everything from in principle, no treatment at all, to very sophisticated coatings with built-in flexible membranes, etc.
Despite the floor being among a structure’s most important components, too little effort is perhaps expended on finding the best and proper covering. This often is because of lack of knowledge and placing all too much trust in the salesman’s cheerful advertising brochures. One can never replace quality with long warranties.
Fundamental for all surface coating systems is that they shall be designed to comply with specified requirements. Simply put, a floor covering consists of two basic elements, namely, the right product and the right execution. If one of these elements is faulty, the covering will also be faulty.
To be able to determine the right product, one must be sure of the requirements specified for the floor, and be knowledgeable of the various products’ functions and properties. The requirements one shall place for the floor are attained through a so-called requirements analysis. Such an analysis can include:
- Mechanical stress on various parts of the floor
- Temperature variations
- Chemical stress
- Freedom from pores
All floors are subjected to mechanical stress but this naturally varies within different parts of a building. To protect the concrete against high point loads, the coating must have a thickness that is determined by the load’s size. Obviously, the coating material must have a compression strength that in itself withstands the load. Many product sheets entirely or partially lack information on mechanical strength.
Floors for truck traffic should never be thinner than 3 mm. For pedestrian traffic, it is often enough with 0.3 mm.
One of the most common reasons for coatings not lasting is that the purchaser chose a coating that was too thin. Practical experience has shown that one can expect load distribution with thickness’s from 3 mm. Extreme loads that arise from impact or from heavy objects being dropped or dragged along the floor can demand special arrangements such as fibreglass reinforcement. See the section Necessary layer thickness for more information.
The floor’s temperature while in use, as well as local temperature variations, is important to know when choosing products. All plastic-bonded coatings have a thermal expansion that is greater than that of concrete. In practice, this means that rapid variation in the floor temperature causes shearing stresses in the concrete-coating boundary layer. Such stress arises, for example, when warm water is spilled on the floor or in front of a bakery oven when the doors are opened. Of the binding agent types epoxy, polyurethane and methyl methacrylate (acrylic), epoxy has the lowest thermal expansion and withstands temperature variations well.
Under normal conditions, floors have a temperature of +15 – 20°C, and the coating material’s properties are adapted to this temperature. If the normal temperature is higher, the coating’s composition should be adapted to this.
Chemicals that will come in contact with the floor coating should be known. In the machining industry, they are often cutting oils, hydraulic oils and solvents, but there are also a number of acids used in etching.
In the dairy branch, there is often lactic acid, and in the chemical industry, nearly anything can be found. The epoxy plastics have very good chemical resistance but there are naturally limits.
In studying chemical resistance lists, one shall be certain of how testing was carried out to be able to make relevant assessments. For example, it can be mentioned that an epoxy coating that is submerged in acetone breaks down relatively fast, but spills of acetone on a floor generally have no affect because the acetone is very volatile.
Anti-skid, i.e. a certain roughness on the surface, is often on the wish list. In dry environments, it is usually unnecessary, but in wet environments and where spills of, for example, oils occur, it is necessary. The degree of anti-skid should be established by assessing a test coating, which will later be the norm in execution.
Cleanability is often related to the degree of anti-skid. Certain types of coatings have built-in anti-skid, which entails that quartz grains in the surface are encapsulated in a scratch-resistant lacquer layer. In this way, both cleanability and anti-skid are attained. Sometimes the requirements for cleanability are very stringent, for example, in nuclear power plants and laboratories. The coating shall then be completely smooth and glossy.
Freedom from pores
In the foodstuffs and pharmaceutical industries, there are naturally substantial demands for coatings being free from pores. Here, the orderer must be very observant. Certain types of coatings, primarily of the type dry mortars and top loaded screeds, can appear free from pores if one looks at the surface. If the coating shall be free from pores and tight, however, each quartz grain must be completely surrounded by binding agent.
The supplier should be able to document tightness and freedom from pores. This can be accomplished with thin grinding or photography of a section in the coating.
That tightness should be considered when planning is perhaps not entirely obvious. One often expects that an epoxy coating is tight, but so-called mortars of coloured sand and binding agent have, for reasons of application technique, too little binding agent. For these compounds, the binding agent content is normally about 15% by weight. Coloured quartz sand is relatively uniform, i.e. the grains are about the same size. For full saturation, binding agent of about 23% by weight is required. This difference cannot be compensated by surface lacquering. The low binding agent content is insufficient to wet the substrate, which is evident if the mortar is laid on a glass sheet. The tightness requirement sometimes demands that consideration be taken to cracking risks in the concrete substrate. Cracks that arise in the concrete after the coating is applied usually result in a crack in the coating. This is because an extension from 0 to something is always an infinitely large elongation, and no coating can withstand this. The only option is thus to first apply an elastic membrane of a few millimetres’ thickness and thereafter a laminate of fibreglass and epoxy, followed by the ordinary coating.
One type of coating is sold just because of its fully open structure. It incorporates natural stone in sizes 4–6 mm that are held together by a very small amount of epoxy, normally 7–10% by weight.
This coating has an attractive appearance and is assumed to save on cleaning costs. This is correct because the open structure has space for quite a bit of dirt. A 15 mm thick coating has space for about 4 litres per square metre. The coating has become very popular, in among other areas, auto-mobile showrooms. What one should not forget is that the open structure also has space for, for example, 4 litres of petrol per square metre, which can entail a very significant fire risk. One should also consider that the total surface area of stones in a 15 mm thick coating constitutes about 10 square metres of exposure per square metre of floor surface.
A floor’s levelness is often of fundamental importance. Examples are high bay storage areas and floors for hovercraft.
Minor unevenness in the substrate is evened out by coatings in thickness’s from a few millimetres and upwards, but large depressions must be levelled before coating. The most advantageous is if the levelling is accomplished with epoxy products instead of cement-stabilized compounds. This pertains to adhesion and surface strength.
Damages that occur because of impact, chemicals or increased temperatures cannot be avoided. Such damages should be remedied as soon as possible to restore function. It can be generally said that epoxy coatings are easy to repair. However, one must expect that a small difference in shade or gloss will make the repair visible for a time.
If possible, the repair should be made with the same material as the coating. It is thus very important that coating work be documented, both by the orderer and the contractor.
When the requirements analysis is complete, it is time to find the products that can be expected to fulfil the set requirements.
Preferably, one should engage a reputable manufacture of epoxy products. If one chooses a supplier with a functioning quality system who is third-party certified, one is guaranteed that the products are well-controlled quality-wise prior to delivery, and that cans contain the right amounts of the right products. Additionally, each package from a quality certified manufacturer is labelled with a batch number, which makes the product traceable back to both final testing and testing for each included raw material. Analysis certificates for the supplier’s products can always be obtained if so requested.
As mentioned in the introduction, a floor coating does not just consist of the right product, but also to a very high degree, the right execution. The installation of a coating is a craft and naturally places requirements on the contractor’s skills, expertise and resources. The contractor must be able to assess the conditions for coating work, both in regards to the substrate’s strength, cleanliness, temperature, etc., and the time it will take to correctly perform each of the various tasks. He should be able to place a quality plan at the orderer’s disposal and be able to document all activities performed that can influence the quality of work executed.