Wooden flooring: the importance of installation

Wood flooring has always had great appeal due to the warmth and natural look they bring into every room. Since wood is a “living” material and grows “old” through the years, installation should always be carried out by experts because they can evaluate the state of the floor, wood type chosen by the customers, the room in which it is installed to provide a state-of-art work.

Proper wood flooring installation involves aspects which only professionals can take into account to provide a state-of-the-art result Wood flooring has always had great appeal due to the warmth and natural look they bring into every room, especially thanks to the latest finishing materials which enhance the beauty of raw material. Compared to other floorings, wood needs particular care during the installation stage, since wood is a “living” material and grows “old” through the years. Therefore, installation should always be carried out by experts because they can evaluate the state of the floor, wood type chosen by the customers, the room in which it is installed to provide a state-of-art work.
Following reviews are taken from the “Wood flooring installation manual for civil use”, published by Edilegno/Federlegno-Arredo, currently a point of reference within this field in Italy. Compared to Northern Europe, in Italy there are no schools for installers with a certification following an introductory training in order to practice the profession. Therefore, there are lots of improvised installers leading to negative consequences for installation.

TYPES OF INSTALLATION

Substantially, parquet can be installed in three ways: glued installation, raised or floating installation, nailed installation on slats dipped in concrete screed or on joists, or on a wooden floor installed on joists or solid-wood or wood based panels. We will consider in detail the first type of installation since it’s the most popular for both solid flooring (traditional) and multi-layered floorings (p finished).

CONCRETE

Besides being the base on which wood flooring is installed, screed is the key element for the installation to be successful. There are three main types: traditional concrete screed, anhydrite concrete screed and fine blacktop concrete screed. There are also other installation surface types: installation surfaces consisting of old floorings, and installation surfaces consisting of wood-based panels. Usually, installers work on the concrete screed laid by the construction company, or more rarely now, by experts in this field. Therefore, before the installation process, it’s hugely important to check the screed conditions, such as compactness across its thickness, adequate thickness for detached screed, rigidity and surface hardness. Moreover it’s important that screed has no cracks and splits, and it is dry, protected from water and steam infiltration and diffusion, smooth and properly cleaned and leveled. Let us discuss in details what is fundamental for installation: seasoning, humidity, protection against water and steam infiltration and diffusion.

Every screed, according to the material it’s made of, needs a proper hardening time and then a proper seasoning time in order to achieve its hygrometric balance corresponding to a certain residual humidity related to climate conditions.
Hardening and drying times of materials used for screeds are different according to the installed thickness and to environmental conditions.

As an example, the following table refers to 20°C with 50 percent Rh (relative humidity).
Generally, concrete screed drying time is a week and a half every cm thickness in dry weather, whereas during wet periods, drying time is doubled. Flooring installation is allowed even if the screed is not perfectly balanced, yet as long as residual humidly stays under the following values. If these values are topped, installation is not allowed, except for screeds treated with proper surface waterproofing products. This treatment is not recommended for surfaces under roof or exposed to constant infiltration. In this case, it is necessary to find out why infiltrations occur, where as for under-roof surfaces, a waterproofing membrane must be laid down, extending up along the wall covering a sufficient portion to protect the floor from lateral infiltration, and then a new screed shall be laid onto this substrate. Humidity is measured with electric or carbide hygrometers. Electric hygrometers measure the electric resistance between two electrodes (nails) fixed into the screed at a given distance.
Electric conductivity in concrete is strongly influenced by its own humidity level and by concrete type, by granule type and their granulometry, and by other elements. Therefore they cannot be used to measure humidity level in screeds reliably (since there are many variables involved), but they can only be used as reference indicators. Carbide hygrometers directly measure humidity level in the screed through chemical reaction, independently of its composition. The test is based on chemical reaction between water and calcium carbide with acetylene formation. The humidity level of the sample, showed as mass, derives from the conversion table supplied with the device.

MATERIALS FOR SUBSTRATE PREPARATION

Once screed features have been checked, specific materials are to be used to restore screed optimal conditions, such as sizes, solidifiers, products for crack filling, waterproofing, leveling and shaving materials.

Gluing

There are different types of glue which can be used to glue floorings to screed or other surfaces:

1) water glues made of water-dispersed synthetic resins modified with strengthening and plasticizing substances;

2) alcoholic glues made of synthetic resins melt in synthetic organic solvents (ethylic alcohol) modified with strengthening and plasticizing substances:

3) two-component glues made of liquid resin modified with different additives and strengthening fillers, and a hardener which is able to react with liquid
resin.
They have no water and contain just few solvents (or noneat all) so that wood is not deformed;

4) one-component, hygro-hardening, polyurethane silanic glues.

Sanding

Wood flooring sanding is basically a surface leveling and smoothing operation. For wood flooring sanding belt or disk sanding machines with abrasives such as corundum (aluminum oxide), silicon carbide and zirconium oxide are used. Proper environmental conditions for a proper wood/environment balance are: 18/22-25 transpiration; 45-60 percent humidity. Only if these conditions are achieved, sanding operation can be carried out. Sanding should be carried out when all rooms have undergone all finishing operations such as wall and ceiling painting, tapestries application and so on. During sanding, environmental conditions should be such to avoid possible further settlements of the wooden flooring. Most of the flooring’s final appearance depends on the sanding operation. Therefore, if sanding is successful, final result will probably be compromised, as the sanding operation cannot be disguised with subsequent finishing operations. Before starting with sanding, floor needs to be cleaned up with a broom or a vacuum cleaner, checking if there are poorly fixed pieces on the floor so that they can be replaced; protruding nails because they would damage sanding machine abrasive and roll; and anything that could possibly hinder the operation. Sanding consists of different passes using a set of abrasives with finer and finer grain. This is usually called roughing: first passes (usually two crossed) to rough the surface, level it and eliminate irregularities. It is carried out with coarser abrasive. Then, actual sanding consists of intermediate passes (usually two crossed) to smooth the surface, eliminate deep scratches due to roughing and prepare the surface for the final stage; finishing consists of final passes (usually two crossed) sometimes carried out with a brushing machine to have a regular and smooth surface for the final finishing treatment (painting, waxing and oiling).

Filling

Sanded-flooring filling is generally carried out using resins and dust obtained from sanding with sanding paper number 120 or, in some cases, with ready to-use pastes. Filling should be carried out before the last finishing pass. In filler and its application, viscosity, wood powder granulometry, and mixing ratio between resin and wood dust are critical.
The filler’s most important properties are: filling cracks without “falling” into them; rapid drying allowing final sanding to be very fast; flexibility of filler submitted to dimensional wood elements variations and to treading stress; adherence to wood and capacity of not staining wood.

Primer

The main purpose of applying a primer is to create uniform surfaces in order to: close pores partially, reduce and uniform wood absorbency, isolate the material so as to prevent the paint from getting in contact with substances in wood causing color alterations; good adhesion of the paint layer; better yield of the finishing coat (better final appearance). The most popular primers are one component solvent- based or two component water-based polyurethane products. According to wood type, choosing the proper primer provides a good paint, just like inaccurate choice might compromise it.

Painting

Painting products are blends of liquid substances which, after full drying and hardening, form a film with certain physical and chemical properties. Hardened paint film protects from stress or external agents; it also delivers higher surface hardness and impermeability to the floor, making it easier to clean and maintain. Parquet finishing is transparent to let the wood grain be visible and offers different brightness grades (glossy, semi glossy, satin, opaque, matte).

Painting product requirements

Adhesion: capacity of adhering to wood and to finishing layer. It depends on resins affinity with wood or other layers.

Penetration: capacity of penetrating wood pores. It depends on: painting product viscosity, pore diameter, pore diameter surface tension, surface tension of painting product and wood or other layers.

Flow: capacity of the product to create a uniform and smooth film (no orange peel effect).

Coating power: capacity of filling pores while leaving the grain visible if applied in thin coats.
This can be achieved applying two or three layers of painting product according to the type of wood.

Pot-life (for two-components products): its the preservation time from the preparation of the blend of two components at 20°C, if the product is kept in the preparation bucket properly closed.

Drying time:

• free of dust time after product application, after which dust in the air no longer sticks to the paint:

• free fingerprint or dry at touch: when, pressing a finger softly onto the surface, no fingerprint is left;

• over paintability time: time span in which paint can be re-painted with another pass;

• sand ability time: when the film is hard enough to be sanded without clogging the sanding paper;

• full hardening: when the film is completely hardened across its thickness, achieving its physical and chemical properties.

Waxes

Waxes for wood floorings are made of both synthetic and natural waxes dispersed in hydrocarbon solvents or in solvent blends containing turpentine essence. Usually waxes are sold as more or less viscose pastes or fluid dispersions. Pastes are used for floor waxing, whereas fluids are used for floor maintaining. Some pastes, called “hot waxes”, are made of particularly hard waxes and can applied only using a brushing machine with special slots. Waxes can be white, uncolored, yellow or darker, to lend specific color shades to treated wood.

Oils

Oils for wood floor treatment and staining are generally made of natural and synthetic siccative oil blends, with variable amounts of mineral solvents. Their hardening occurs both through solvent evaporation and through oxypolymerization due to atmospheric oxygen. Oils application doesn’t create a surface film but a proper staining with wood porosity saturation, maintaining good breathability, therefore normally wood becomes darker.

Do-it-yourself installation? No, thanks!

From what we have explained so far we have just given general concepts without going through technical details it clearly comes out which and how many aspects are hidden in a state-of-the-art wood-flooring installation.