All information on this page is copied material from Gulvfakta, which is a technical reference material, Source: Gulvfakta

5.3.0.1 Introduction
This section mentions:
• Requirements for takeover before grinding begins.
• Instructions on the method for sanding different types of wooden floors and associated outcome requirements.
• Requirements for acceptance before surface treatment begins.
• Instructions on methods for surface treatment of different wooden floor types and associated outcome requirements.
Cleaning wooden floors is not mentioned here. Reference is made instead to the section Cleaning wooden floors

Wooden floors have been used in the Danish building tradition for centuries. The background for the many years of use is that wooden floors have a beautiful appearance and great wear resistance and thus a long life. In addition, wooden floors are pleasant to stay on. There are many different types of wood, which in this section are divided into soft wood species, especially conifers, and hard wood species, especially hardwood and exotic wood species. Both in connection with renovation and in new construction, wooden floors are sanded and surface treated to an ever greater extent. It is important that this work is carried out in a professional manner.

In order for this to be achieved, it should be described in the tender phase exactly which requirements there are for the finished result, e.g. in terms of flatness, the strength of the surface treatment and the extent of visible pinholes or scars that can be accepted. Many different materials are offered for the surface treatment of wooden floors. When choosing a surface treatment, it is important that both conditions of use and appearance are carefully considered. Cleaning and maintenance plans must be drawn up in order to ensure the floor's appearance and wear resistance, see more about this in the section on Cleaning. When designing sanding/surface treatment, reference should be made to this section on Gulvfakta's website. This ensures that the bidders give a price and carry out the work according to the same guidelines and quality standards. When preparing the instructions in this section, the flooring industry has largely taken as a starting point the experiences and practices of the supplier members.

5.3.0.2 Construction site conditions - prerequisites
If the work takes place on floors other than the ground level, mechanical transport should be available to transport the floor sanding machine. A waste container is assumed to be available. Free access to electricity is required - preferably 380V/16 A - as floor sanding machines are very power-demanding. In the vast majority of private homes, there is only access to 230V/10 A. In residential installations of recent date (diaset and neoset fuses), fuses of 230V/13 A can be used. It is necessary that all other unnecessary loads are switched off from that group , which must pull the floor sander. Sanding wooden floors is dusty. A decision must therefore be made as to whether there is to be cover to adjacent rooms and objects located in the room or rooms where sanding is to be carried out.

Houseplants and livestock as well as coated paper, e.g. fax and photocopy paper, can be damaged and should therefore be removed before surface treatment is carried out.

Temperature and humidity in air and in wood
Before the work is carried out, the building must be closed and dry, and the building must be heated. During the entire execution, the temperature must be 17-25°C and the humidity 35-65% RH. The wood's moisture content should be between 7 and 12%. During the execution of the surface treatment, drafts must not occur.
Quality requirements
In order to achieve a satisfactory quality of the sanding work and the subsequent surface treatment, it is important that the tender documents describe exactly what is to be carried out and what outcome requirements are expected from the finished work. General construction site and temperature conditions etc. are described above. In the following sections, specific requirements regarding the takeover of the floors and expected outcome requirements are described. Furthermore, there are specific outcome requirements set out in each job description regarding surface treatments.

Takeover requirements
Upon takeover, the following requirements must be met:
The floor must lie firmly and be stable, otherwise inappropriate marks/scratches may appear after sanding. Any major damage must be repaired when lice are removed. Nails or screws must be sunk/recessed min. 2 mm. (It is necessary to sink/countersink nails and screws to avoid damaging the sanding paper/roller, as well as to counter the risk of sparks being emitted which could ignite the sanding dust in the dust bag). The floor surface must be free of grease, mortar blobs, putty, glue, paint, silicone, etc. All sand strips along edge restrictions (walls) as well as sweep strips by doors should be removed so that sanding can be done all the way to the edges.
ATTENTION! The wear layer in older slatted boards can loosen during sanding and surface treatment. The reason may be small vibrations and heat generation from the sanding machine. When painting, surface tension in connection with the hardening of the paint can also lead to adhesive failure between the wear layer and the underlying layer.
Sanding and subsequent surface treatment of wooden floors should be carried out as late in the construction process as possible to avoid damage to the floor from other craftsmen. However, the last painting of woodwork must wait until after sanding and possibly surface treatments of the floor have been completed, as minor damage may occur to adjacent walls and woodwork. If there is underfloor heating, the temperature must be lowered to a normal room temperature (20-21 °C). The temperature of the underfloor heating system must not be raised again until 5 days after the surface treatment has been carried out. The temperature in the underfloor heating system must never exceed the maximum temperature set by the wooden floor supplier.

Outcome requirements - grinding
In general, after finishing sanding, the floors must comply with the following:
• The floor surface must be flat and even, and there must be no visible gaps between the individual boards/poles. The surface must be without a visible "washboard effect".
• The floor surface must be sanded to clean wood.
• There must be no "grinding stops" or "transitions" between grinding the surface and along edges and in corners.
• The floor, assessed at normal standing height (1.6 m above the floor), must appear smooth, and there must be no visible scratches.
• It is recommended that cam holes larger than 10 mm in diameter and/or more than 5 mm deep, as well as nail and screw holes, are filled with suitable material.
Clean wood means that the surface after sanding is completely free of the old surface treatment. For varnished floors, this means that there must be no varnish residue in the wood.
After finishing sanding, floor surfaces as well as adjacent horizontal surfaces (footboards, window sills and the like) must be vacuumed for reasons of subsequent surface treatment. Wood is a natural product that changes color when exposed to light. There may therefore be color differences after finishing sanding if the floor has been exposed to different light effects.
Outcome requirements - surface treatment
In general, after finishing the surface treatment, the floors must comply with the following:
• The surface must appear uniform and smooth and without visible transitions.
• There must be no air bubbles or significant impurities in the surface.

Figure 1. The washboard effect can reappear in wooden floors that are not protected against moisture from below.

Smaller dust particles in the surface may occur because a dust-free environment cannot be achieved. Small dust particles on the surface are quickly worn away by cleaning and using the floor. It is recommended to make a sanding and treatment test before starting the work to determine the quality. Such a grinding and treatment test is billed separately.
Machines
The most frequently used machines on the market are belt and roller sanders for large surfaces. There are also planing machines for leveling old floors made of soft woods.

For edges or hard-to-reach places, edge and beak sanders are used, respectively. For stairs, edge grinders in smaller models or eccentric grinders are used.

In addition, a disc/polishing machine with a sanding net and/or various polishing pads is used.

Common to all machines is that there should be a built-in vacuum cleaner with a dust bag. What is special about belt and roller sanders is that they must always be precisely set so that the pressure against the floor is the same, i.e. that the rollers must sit completely straight. The rollers must be kept clean to achieve the best result, i.e. free of dust and stuck-on particles, e.g. paint residues. Cleaning of rollers should be done with compressed air. The rollers should be checked regularly, and always after transporting the machine.
Environmental requirements, including personal protective measures
When sanding, it cannot be avoided that fine dust spreads in the air. In addition, grinding machines make a lot of noise. Other people should therefore not work or stay in the areas where grinding takes place. The person carrying out the sanding must protect himself with the legally mandated protective measures in the form of a respirator with associated filters and hearing protection. It is recommended to use a grinding oil with a low grinding code. The supplier's instructions for use must be followed. The packaging for surface treatment products, abrasive oils, etc., must be labeled in accordance with applicable legislative requirements. Instructions for use and safety data sheets must be available at the workplace. For environmental reasons, all product residues should be handed over to the local chemical depot.
Fire and safety requirements
Sanding dust is easily flammable and flammable, and the sanding dust must therefore be removed immediately. Products for surface treatment are also easily flammable, why used rags etc. must be poured over with water and placed in plastic bags. If the cloths are to be reused at a later time, they must be stored in a suitable metal container with a tight-fitting lid. Good ventilation must be ensured until the surface treatment is dry.
Covering etc.
In general, sanded floors should be surface treated immediately to avoid soiling. If this is not possible, the floor must be covered with suitable material depending on which activities/traffic are expected.
For further information on covering, refer to the section on accessories and special materials.

If covering is carried out after the surface treatment, the instructions from the supplier of the surface treatment must be followed. Cover must be vacuumed before removal. It is recommended to finish oiled floors before use. Be aware that wood is a natural product that changes color when exposed to light. There may therefore also be color differences after covering if the floor has not been uniform and fully covered.

5.3.0.3 Work description for grinding
Sanding of wooden floors is described for the following types:
• Wooden floors laid as long sticks
• Wooden floors laid in patterns (herringbone, glazed parquet, mosaic parquet, etc.)
• Cork floors
Sanding of old and new floors is described together.

New wooden floors that have been surface-treated from the factory must be treated according to the wooden floor supplier's instructions. New untreated wooden floors must be sanded so that the quality requirements are met. Sanding of stairs takes place according to the same guidelines as for floors, however other machines are used, cf. the section on machines.
Receiving control
Before sanding, a determination must be made of the thickness of the floor's remaining wear layer on laminated floors and the thickness of the top lip of the groove on solid floors. On slatted floors, the safest way to do this is to take a drill sample. Slatted floors with a wear layer of 2 mm and below cannot be sanded. The residual thickness of solid floors can usually be measured with a thin metal blade in the tongue and groove joint.

Wooden floors laid as long poles
Wooden floors laid as long sticks can be made of:
• Slatted boards
• Parquet boards
• Stavparket
• Floor boards

The procedure for preparation is as follows:
• A receiving inspection of the floor is carried out.
• The stability of the floor and the thickness of the wear layer are examined.
• Nails and screws are submerged.
• As extra work, it can be agreed that cam holes and the like larger than 10 mm in diameter and more than 5 mm deep as well as nail and screw holes are puttyed with suitable material in the same type of wood.
The condition of the floor determines the type of sanding to be carried out, including which starting paper and any intermediate papers to be used. The entire floor surface is polished longitudinally by the boards/sticks.

After finishing sanding, both the floor surface and adjacent horizontal surfaces (footboards, window sills, etc.) must be vacuumed.

Wooden floors laid in patterns (herringbone, glazed parquet, mosaic parquet, etc.)
The procedure for preparation is as follows:
• A receiving inspection of the floor is carried out.
• The stability of the floor and the thickness of the wear layer are examined.
• Nails and screws are submerged.
• As extra work, it can be agreed that cam holes and the like larger than 10 mm in diameter and more than 5 mm deep as well as nail and screw holes are puttyed with suitable material in the same type of wood.
• The condition of the floor determines the type of sanding to be carried out, including which starting paper and any intermediate papers to be used.
Wooden floors laid in patterns are usually sanded first diagonally and then in the lengthwise direction of the room. Alternatively, the floor can be sanded in the direction from which the light comes. The entire floor surface is polished in the direction from which the light comes. After finishing sanding, both the floor surface and adjacent horizontal surfaces (footboards, window sills, etc.) must be vacuumed.

Cork floors
It is being investigated whether the cork floor can be sanded. It is recommended to make a sanding and treatment test before starting the work to determine the quality. Such a grinding and treatment test is billed separately. The thickness of the cork is also determined below. Please note that cork tiles can have a vinyl surface. In that case, the floor cannot be sanded nor treated according to the guidelines in this section. The cork floor is finally sanded with net or paper and finished with an elastic surface treatment agent such as hardening oil or elastic varnish. Lacquer treatment is repeated at least 3 times. Oil is applied until the floor is saturated.

5.3.0.4 Outcome requirements for grinding
After finishing sanding, the floor must comply with the following:
• The floor surface must be flat and even, and there must be no visible gaps between the individual boards/sticks/cork tiles. The surface must be without a visible washboard effect.
• The floor surface must be sanded to clean wood/clean cork.
• There must be no "grinding stops" or "transitions" between grinding the surface and grinding along edges and in corners.
• The floor, assessed at normal standing height (1.6 m above the floor), must appear smooth, and there must be no visible scratches.

5.3.0.5 Surface treatment
The purpose of surface treatment
The purpose of surface treatment of wooden floors is to protect the wood from wear and tear, to prevent/limit dirt or liquid spillage from penetrating the wood and to give the wooden floor the desired appearance. Wooden floors are supplied untreated or surface-treated from the manufacturer, especially depending on the type. Parquet boards and slatted boards are normally supplied with surface treatment, as it is not necessary to carry out finishing treatment of the surface after the floor has been laid. Parquet floors laid from single sticks, mosaic parquet and brick floors, on the other hand, require sanding after laying, and are therefore surface treated only after the floor has been laid. Laminate floors cannot be surface treated. When the laminate is worn out, the floor must be replaced.

Surface treatment can be used:
• Lye treatment
• Soap treatment
• Oiling
• Wax treatment
• Varnishing

The surface treatment of wooden floors must be repeated from time to time to remove soiling, to renew the protection and to maintain the desired appearance. When choosing a surface treatment, the type of wood and the desired appearance should first of all be taken into account. All types of surface treatment can be used under several different conditions of use, but the required maintenance effort will vary depending on the type of surface treatment, intensity of use and type of use. Also be aware that for some types of wooden floors, the appearance of the floor is significantly changed by surface treatment. This applies, for example, to for wooden floors with a brushed surface. With traditional sanding, the brushed surface will disappear, leaving a flat and smooth surface. Maintenance of the varnish is therefore particularly important for this type of floor. For all types of floors, it is important to make clear from the start at which intervals care and maintenance are required, in order to ensure a satisfactory appearance. In particular, there can be a conflict between appearance and economy if a floor that requires a lot of maintenance to maintain the desired appearance is used where there is a high intensity of use. Cleaning and maintenance of wooden floors is closer to the Cleaning section.

Spruce and pine are suitable for both varnish, lye, wax, soap and oil treatment. Oil and oil with wax are often chosen for treating the dark wood species because of the beautiful glow the wood gets. In addition, oil has the advantage that heavily trafficked areas can be partially repaired, in contrast to e.g. varnish, which usually requires a repaint of the entire floor. Maintenance of oil- and wax-treated wooden floors requires the knowledge of the person in charge of the daily cleaning and maintenance of the floor. It is therefore recommended that maintenance instructions are given before it is started. A product description and cleaning and maintenance instructions for the surface treatment products used must always be submitted. Safety data sheets for the surface treatment products used to maintain the floor can be requested from the supplier. When choosing a product and method, both the wooden floor supplier and the surface treatment supplier should be consulted, so that the optimal treatment in relation to the type of wood, intensity of use, etc. secured. With all types of surface treatment, smaller dust particles may appear on the surface, which will disappear during the ongoing cleaning and use of the floor. Surface treatment of stairs takes place according to the same principle as for floors. However, it should be noted that the wear and tear on stairs is usually greater than on floors.
Protection of wooden floors
To reduce soiling and damage, entrance areas with soil prevention measures should be used, e.g. a combination of scraper grate and mat arrangement, which ensures that dirt and moisture are removed from the footwear before walking on the floor.
Lye treatment
Lye treatment is not a surface treatment, but a preparation for a surface treatment, e.g. with soap, wax or oil. Lye treatment delays the natural yellowing of the wood.

There are 2 types of ready-made lye:
• Softwood liquor, which is used on pine, spruce and pitch pine.
• Hardwood slush/beech slush, which is used on light solid hardwood floors.
• Dark woods should not be treated with lye.

It can be risky to lye treat laminated parquet floors with a hardwood wear layer, as the wear layer can detach from the supporting layer (delaminate). The wooden floor supplier should therefore be consulted before choosing a product.

• Before lye treatment, the floor must be sanded to clean wood. The floor must be clean and free of grease, soap, wax or any lacquer residue.
• The floor must be dry before starting the lye treatment.
• The lye is applied to the floor in an even layer with a roller, mop, brush or similar. The procedure must follow the supplier's instructions.
• The floor must then dry. The drying time depends on the product.
• When the floor is dry, sand it with a circular sander with polishing pads in green or blue. The floor is vacuumed before the desired surface treatment is applied.

For surface treatment can be used:
• Soap
• Wax
• Oil
Soap, oil and wax treatment are discussed in more detail in the following sections.

Soap treatment
Soap is available as natural soap and as white lye soap.

Lye soap must not be used on varnished floors.

Natural soap can be used on all types of wood. White lye soap may only be used on light wood species. When using white lye soap, it must not be expected that the characteristic white-grey color will be achieved on the first application.
• The soap is mixed according to the supplier's instructions and applied to the floor in an even layer with a floor cloth, mop or machine. The floor is then dried with a hard-wrung floor cloth.
To achieve the best protection, at least 2 soap treatments should be carried out before the floor is put into use. On hard wood species, a minimum of water must be used when soaping.
Result requirements: Saturated, uniform surface without overlaps, with a white-gray silky matt gloss. The surface must not be rough.

Oil treatment
Unpigmented and white-pigmented wood floor oil is available. Oil with wax is also available. A distinction is made between hardening and non-hardening oil, each of which has different properties and requirements for maintenance intensity. UV-finished wooden floors are also available, i.e. floors that are delivered from the factory with a finished oil treatment, which does not require further treatment, but can be used immediately after laying. In principle, all types of wood can be treated with oil. However, the supplier should always be consulted when choosing a product. When using oil, the procedure must follow the supplier's instructions, as there can be a big difference between the working methods.

However, a typical approach is the following:
• First, the floor is sanded to clean wood.
• The floor is then fine-sanded with mesh 120 and vacuumed thoroughly.
• The oil is applied immediately afterwards in a thin, even layer with swabs with wool fabric, rubber scraper (acid-resistant) or roller in the lengthwise direction of the wood.
• Consumption and application depends on the type of wood and the condition of the floor, cf. the supplier's instructions.

Curing oil
• Oil is applied until the wood is saturated on the surface. Excess oil is removed with cotton cloths on a polishing machine or manually within the time specified by the supplier (approx. 20-30 min.), otherwise shiny shields from dried oil may appear.
• After oiling, the floor is polished with a circular sander with polishing pads and oil according to the supplier's instructions.
• Finally, wipe the floor with a lint-free cotton cloth until the surface appears with a silky matt shine.
• After the specified drying time, the floor can be used. The drying time will be stated in the supplier's instructions.

Result requirements: As oiling is an impregnation, the floor should appear with a uniformly saturated surface, without overlaps and with a uniform gloss. There must be no surface film of dried oil. The oil should be in the wood and not on the wood. When oiling newly laid floors and floors that have been sanded clean, it will usually be necessary to repeat the above processes several times to achieve a saturated and uniform surface. The first oiling is recommended to be done with a base oil, the subsequent ones with a maintenance oil. In each process, exactly the amount of oil that the floor can absorb/absorb should be applied and excess oil should be removed.

The number of oilings should be included as part of the basis of the agreement. If nothing else has been agreed, an oiling of a newly laid floor, or a floor that has been sanded clean, includes a basic oiling and a maintenance oiling.

Non-hardening oil
• Oil is applied until the wood is saturated on the surface. After approx. After 1 hour, the oil is distributed again and more oil is applied to the absorbent areas.
• After approx. After 24 hours, the floor is polished with yellow or white polishing pads on a circular sander and re-polished with dry floor cloths.
• Finally, polish with crepe paper on a polishing machine, possibly with heat.
After the specified drying time, the floor can be used. The drying time appears from the supplier's instructions. Non-hardening oil should not be used on wooden floors without tongue and groove, which lie on an asphalt base, as this can cause discolouration in the wood. Furthermore, the use of non-hardening oil on the laminated parquet is not recommended unless the wooden floor supplier has approved this.

Result requirements: As oiling is an impregnation, the floor should appear with a uniformly saturated surface, without overlaps and with a uniform gloss.

UV curing oil
• UV-hardening oil is used exclusively for factory oiling. The oiling is carried out by rolling the oil onto the wood in a mechanical process, after which the oil layer is irradiated with UV light. Due to the special composition of the oil, curing with UV light takes place within a few seconds.
• UV-oiled wooden floors usually do not require any finishing. The floor can be used immediately after laying, but after use the floor must be continuously maintained according to the wooden floor supplier's instructions. When polishing floor surfaces, only soft cotton cloths should be used. The use of the sanding net and coarse polishing pads is not recommended.

If the floor is damaged during installation, repairs should only be carried out in accordance with the wooden floor supplier's instructions. The interval for maintenance with care oil depends on the floor's place of use and traffic intensity. However, it is important that the oil does not wear through, because it is difficult to achieve a satisfactory uniform surface when repairing worn areas. Heavily stressed areas in homes, e.g. kitchens, corridors and the like. may require maintenance oil several times a year, while it may be years before areas with less traffic, such as bedrooms and living rooms, require oil maintenance. In public environments, e.g. cafes, shops and the like. in places where outdoor footwear is used, it may be necessary to apply care oil to the floor several times a week. It is therefore recommended that specific care instructions be drawn up for these areas. Repairing damaged floor surfaces can be difficult and should only be done in accordance with the wood flooring supplier's instructions. For heavily damaged surfaces, it may be necessary to sand the floor to clean wood and then carry out a traditional oil treatment.
Wax treatment
Wax for surface treatment is available for both untreated and lye-treated wooden floors. Both unpigmented and white-pigmented wax are available for wooden floors. White floor surfaces are delicate and therefore require frequent maintenance. The wax supplier should therefore be consulted if this type of surface treatment is desired.
Freshly sanded floors
• The floor must be sanded to clean wood and be free of wax, grease, lacquer and the like.
• The floor is vacuumed thoroughly for residues of sanding dust and other impurities.
• The wax is applied with a felt roller in an even layer. A brush is used along edges and other hard-to-reach places. The procedure must follow the supplier's instructions.
• After 6-8 hours, the floor is polished with a polishing machine or manually.
After the specified drying time, the floor can be used. The drying time appears from the supplier's instructions.
Lye-treated floors
The floor is thoroughly cleaned of soap film and vacuumed until the surface is completely free of dust and dirt.
• The wax is applied as described under freshly sanded floors.

Outcome requirements: Saturated, uniform surface without overlaps and with a silky matt gloss. The surface must not be rough.

Varnishing
• Varnishing is a surface treatment which forms a film of a few hundredths of a mm thick on the surface of the wood. The varnish can help to emphasize/preserve the natural colors of the wood.
• Varnished floors can usually be used for a long period before it is necessary to re-treat. In homes, the lifespan will often be several years.
• Lacquer is resistant to the most common household chemicals and is available in different qualities for use in both homes and rooms with greater load.

There are different types of 1- and 2-component, water-based and solvent-based varnishes on the market. The paints most often consist of a system where a base coat is first applied and then finished with a top coat.

New untreated wooden floors and wooden floors that have been sanded to clean wood should be primed to reduce the risk of lateral bonding/gluing. It is recommended to contact the paint supplier, who can recommend products for base coating that prevent side bonding. It is not recommended to use water-based varnish on wooden floors made of Maple that have been sanded to clean wood. Maple can contain sugar crystals, which when exposed to water can cause reddish-brown spots on the surface of the wood.

When choosing a varnish, it is important to assess how much wear is expected in the area in question. There are special varnishes for areas that are exposed to a lot of wear and tear. In the past it was necessary to use isocyanate varnishes, but today water-based varnishes with similar wear resistances are produced.

Most varnishes can be used both for new floors and for repainting. However, acid-hardening varnish cannot be used for repainting water-based varnish. The varnish supplier should always be consulted.

Freshly sanded floors
• The floor must be sanded to clean wood and be free of wax, grease, lacquer and the like.
• The floor is vacuumed thoroughly for residues of sanding dust and other impurities.
• Primer is applied to the floor in an even layer with a roller or brush. The procedure must follow the supplier's instructions.
• After basecoating or the first top coat (depending on the supplier's instructions), intermediate sanding with fine sandpaper or sanding net. The floor is then vacuumed thoroughly.
• Finally, top coat is applied.
Consumption and drying time according to the lacquer supplier's instructions.

Outcome requirements: Saturated uniform surface without overlaps and with a uniform gloss.

Varnished floors - refinishing
• The floor is vacuumed thoroughly and washed for soap residues, dirt etc.
• The floor surface is then intermediately sanded with fine sandpaper or the sanding net.
• When re-varnishing new factory-varnished boards, extra thorough intermediate sanding (matting of the varnish surface) must always be carried out. It must also be ensured that the varnish used is compatible with the factory varnish.
• The floor is vacuumed thoroughly and wiped with a damp, hard-wrung cloth.
• Topcoat is applied to the floor in an even layer with a roller or brush. The procedure must follow the supplier's instructions.
One or two layers of topcoat are applied with drying time and intermediate sanding between each coating.

Consumption and drying time according to the lacquer supplier's instructions.

Outcome requirements: Saturated uniform surface without overlaps and with a uniform gloss.