Unless the subfloor, the screed, the moisture barrier, the adhesives, the underlay, or whatever else is needed to provide a perfectly installed floorcovering is correct, the floor will not perform in accordance with the specification, and may even fail. More than often the floor itself is blamed, but it’s the substructure that has failed.
Substrates and slabs
The most common substrate provided for any floorcovering is a concrete floor slab. In the case of a ground-floor slab, this in situ floor slab can be direct-finished by power-floating, or provided with a screed or topping to provide the required finish.
In the case of suspended slabs, the in situ concrete can be directly finished, or a screed or topping (as indicated above) can be used. Suspended floors can also be constructed using precast hollow-core concrete planks or even beam and block systems. Such floors often require a structural concrete topping to ensure structural integrity. This topping can be floated to the required finish.
In many cases chemical admixtures may need to be added to the concrete mix: to modify some of its properties (such as increasing its workability and reducing water content to increase strength); to compensate for poor aggregate properties; to reduce total cost; and many others.
In floor-on-the-ground applications it will be necessary to provide joints in the floor or to reinforce the floor with reinforcing mesh, conventional reinforcement or steel fibres to control cracking. Such joints must be continued through any screed or topping and, in some cases, the floor finish or covering as well. Professional advice should be sought from the Cement & Concrete Institute (011 315 0300/ email@example.com/ www.cnci.org.za) to ensure that the jointing or reinforcing is correct for the application.
Precast floor options offer several advantages over in situ floor casting, including speed of erection, lower building costs and consistent quality levels. Also, the use of high-strength concrete, coupled with pre-stressing, means that hollow-core slabs can achieve considerably larger spans than in situ reinforced concrete slabs of similar depths.
However, the fixing of ceramic tiles or most other hard floorcoverings onto any concrete suspended floor slab requires special attention if cracking is to be avoided.
Flexible adhesive is the answer, nevertheless several basic rules must be followed to ensure success, and the Concrete Manufacturers Association (www.cma.org.za) has produced a comprehensive list of brochures and pamphlets on concrete floor slabs, so it would be a wise move to contact them before making a decision.
Screeds & Toppings
Before we proceed with further things one finds ‘Below the Surface’, we should touch on the all-important screeds and toppings which, if not applied correctly, often result in failure of the floorcoverings.
Screeds are essentially light-duty flooring elements and are suitable for wearing surfaces of floors of utility rooms in domestic premises (storerooms, garages); and of floors covered with carpets, plastic tiles or linoleum, and subjected to relatively light traffic such as in offices, shops and hospitals.
Screeds are generally not suitable as wearing surfaces in commercial buildings, schools or industrial premises. Preferred methods of floor construction for such premises are full-thickness, trowelled concrete or a topping on a concrete base.
Screeds and toppings should be specified only where placing and finishing the concrete floor to acceptable standards is impractical.
Although available in a range of colours, screeds are generally carriers for other flooring systems such as vinyl flooring, where an exceptionally smooth surface is a necessity.
It must be remembered that the characteristics of screeds and toppings may differ considerably depending on the use to which they will be put, so it pays to seek the advice of an expert, or pose your questions to the Cement & Concrete Institute to get the correct answers.
It is essential with modern floorcoverings that the subfloor be adequately protected from external dampness, because many problems that occur with floorcoverings adhered to the subfloor are as a result of moisture in the subfloor due to lack of a damp-proof membrane in the structure; an inefficient or faulty membrane system in the structure; or residual moisture in the subfloor.
This means that damp-proof membranes can be laid beneath the concrete base slab (recommended), or onto the base slab and topped with a screed/topping at least 50mm thick (not recommended), or applied to the surface of the slab.
They are generally polythene membranes, but can also be hot-applied bituminous compositions; cold-applied bitumen or rubber/bitumen emulsions; or polythene membranes (some coated with self-adhesive bituminous compound or similar) – depending on the application and the potential problem.
Make sure the flooring contractor conducts a moisture test on the subfloor before installing the floorcovering.
Underlayers and subfloors
These are very important aspects of any flooring project in both residential and commercial applications. Their proper selection and installation is crucial to the proper wear and stability of any floorcovering. As the quality of the finished floor will only be as good as the subfloor over which is has to be laid, the importance of using an underlayer can’t be stressed enough, regardless of the type of floor being used.
The underlayer sits between the substrate and the flooring material, and is meant to absorb the roughness or imperfections of subfloors, so that the floorcovering can be installed on top of a smooth, hard surface that will give the material extra support.
Underlays for soft flooring like carpet are very different from those for hard surfaces, and others may be required to perform certain functions, such as providing a moisture barrier, sound deadening, or cushioning.
Whatever floorcovering is anticipated, the underlay requirement should be discussed with the manufacturer or supplier before materials are ordered or installed.
This is the next operation before the final floor material is installed, and here the choices are definitely ‘horses for courses’. With the accent on ‘green’ these days, considerable developments have been made by the adhesives industry to meet demands for the use of fewer volatile organic compounds (VOCs), thus reducing emissions and odours that can contribute to respiratory problems and poor air quality in buildings. Look out especially for adhesives with very low or no VOCs which are tested and marked with the GEV-EMICODE® EC 1 label.
Ostensibly, flooring adhesives are a combination of binders (polymers and resins) that provide adhesion; fillers (usually very fine aggregates) that provide volume and a better working consistency; and a liquid (water and/or solvent) so that the adhesive is workable during application and as it dries adhesion is achieved.
This means that acrylic-based and pressure-sensitive adhesives have become popular with flooring contractors who demand high performance from adhesives when fitting vinyl floorcoverings. Pressure-sensitive adhesives that can be allowed to dry completely before fixing are also becoming increasingly popular.
Before the installation can be started, it is necessary to prime the already prepared concrete slab with a primer. Usually this is an acrylic-based, solvent-free primer.
After drying, a cement-based levelling compound will be applied in a thickness of 2-3 mm, to provide a very smooth and constant absorbent surface. This is necessary under all kind of adhesives.
Vinyl, PVC, rubber and hardwood floorings can be installed using a two-part polyurethane adhesive. This product is a reactive resin system where two components are mixed together and a chemical reaction takes place so that it cures and hardens sufficiently in 4-6 hours to take foot traffic.
Wood flooring with a traditional tongue-and-groove fixing system that needs an adhesive should use a one-part polyurethane or a one-part SMP adhesive because it has an elasticity for a bounded movement especially for planks that always takes place once installed.
This type of adhesive is also used where floors are required to be stuck down, although a damp-proof sealer or moisture barrier should be applied to the substrate before installation in these cases.
The most common types of wood flooring adhesives include water-based adhesives certified as ‘very low emission’. Especially, GEV-EMICODE EC 1 tested and labelled products will guarantee that they are free of solvents or VOCs and safe to install. However, their range of application concerning certain types of wood or subfloor is limited.
Solvent-based adhesives have been well proven for wood floor installation over many years, but the non-hazardous solvents which they contain are said to evaporate during the first weeks after installation is completed.
Usually more expensive than other adhesives, SMP or urethane-based/moisture-cure adhesives offer the largest range of application and the highest installation security.
The latest innovations include an elastic adhesive which is an adhesive mat for laying floors; a new fixing system which makes the use of screws, nails, glue or clips obsolete for the laying of parquet and strip floors.
The three main categories of setting materials that are used for ceramic, porcelain and natural stone floors are mastics and cement mortars, and epoxy or urethane adhesives. Mastics are premixed and easy to use, but they are weak compared to cement mortars and don’t like exposure to water, so they are not recommended for floors in wet and also not in dry areas.
Epoxy adhesives are commonly used for industrial or pool applications. These are usually high-performance, two-component, epoxy-based adhesives used for a variety of materials, ensuring full bond and maximum adhesion to these components.
Cement mortars, of which there are several varieties, are strong and can stand up under exposure to water and other stresses that a tile installation may undergo.
Cement mortars are often called ‘thinset mortars’, which come in powder form and must be mixed with either water or an acrylic additive (some powdered thinsets have an additive already blended in); these have a stronger bond and are more flexible than pre-mixed adhesives.
Cement-based tile adhesive is used for general tiling on solid concrete floors, and is generally cheaper than other types of tile adhesive, but it should not be used on cracked cement floors or where there is the influence of acid-based chemicals or cleaners or where some movement is expected. It is supplied dry and is mixed with water before being applied.
Modified cement-based tile adhesive is often used to cope with small amounts of movement. It contains polymers so that if the tile moves slightly it will not crack. For example, on concrete or over floor heating systems or for big ceramic tile sizes.
Fast-setting tile adhesive is used when the tiles need to be in service within four hours. For example, ceramic floor tiles can be walked on within four hours. Especially this kind of adhesive will be used for the installation of water-sensitive, natural stone coverings.
Carpet adhesives come in two main types. There are adhesives that come pre-applied to carpets that facilitate installation; other adhesives are in a spreadable form and must be applied to the carpet backing with a trowel or roller – but the right adhesive must be used for the type of backing on the carpet, otherwise the installation will be affected.
For more detail, and an update on the latest technology in flooring adhesives, look out for our annual feature in the next issue of FLOORS in Africa.
So now we have dealt with everything that is needed to support, keep dry and stick down floorcoverings. Let’s take a look at other benefits to the end user that can be found ‘Below the Surface’, of which probably the most efficacious is the heating of the floor surface.
Although quality underfloor heating has been available in South Africa for over 25 years, it seems that the residential market has finally taken to the idea of heating homes in winter.
This demand has, of course, caused a proliferation of ‘experts’ in the marketplace and one can expect that there are now a lot of charlatans out there, so it would be a wise decision to use only those systems that have a proven track record of quality, performance and customer service over several years.
The old underfloor heating systems were inside or even under the screed, so the concrete had to be heated before any effect was felt in the room. The modern surface floor heating elements are fitted on top of the screed directly under the surface floorcovering, thus getting the room to the required temperature much faster.
Thermostatically and timer-controlled, these modern systems provide the heat when and where it is required and, with a wide variety of options, they can be used with any type of floorcovering.
They are also cleaner because no fossil fuels are used; they emit no smoke or dust, or noise; and no more queuing for bottled gas when the weather turns really cold!
Access floors; cable management and airconditioning
With thousands of square metres of office space now fitted with raised access floors throughout South Africa, it has become normal practice for the design of new buildings (or even the retrofitting of old ones) to include this facility.
This not only increases the asset value and the rental capability quite considerably, but it ensures an extended lifespan in providing the adaptability that office churn or tenant changes demand.
In more specialist applications such as operating theatres, ICUs, call centres and anywhere that has a high electronic requirement, an access floor or a quality cable management system becomes imperative.
Installations devoted solely to cable distribution could be as low as 75mm although, when incorporating air distribution systems, plenum depths can range up to one metre. Floor voids for modern airconditioning need be no more than 300-350mm, but the access floor must also accommodate the ducts, grilles and other equipment related to the building’s HVAC system.
This is such a vast subject that space restrictions for this feature apply, but anyone wishing to know more about this final ‘hidden’ benefit should refer to the first issue of FLOORS in Africa for 2012 where it was covered in some detail.