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

1.7.4.1 Checklist for laying

Checklist for laying non-load-bearing floors.
1. The relative humidity in the building must be between 35 and 65%, depending on the season, and the temperature approx. 20°C.
2. The building must be closed and the heating system must be installed and in use.
3. The subfloor must be dry, see also the section on moisture measurement.
4. For subfloors made of inorganic materials, this will mean a pore moisture of max. 65%. Subfloors made of organic material must be in equilibrium in relation to the season. If the subfloor is not dry, you must either wait before laying the floor or carry out a moisture barrier. The moisture barrier must be adapted to the product and installation method.
5. Insulation materials, etc. must be dry.
6. Wooden floor materials must have a moisture content of 8 ± 2%, of which 2/3 of the lot should be between 7 and 9% moisture content.
7. Wooden floor materials dried to the conditions of use should not be unpacked before laying.
8. Time must be set aside for wood that is not delivered dried to come into equilibrium with the temperature and humidity conditions in the room.
9. Wooden floor materials, glue, sealant and other auxiliary substances should be acclimatised in terms of temperature for at least a day before use, e.g. when stored in the rooms in which they are to be used.
10. Substrates must be flat with deviations of no more than ± 2 mm in 2 m and without burrs and ridges.

1.7.4.2 Floating floors

Description.
Floating wooden floors form a continuous surface and can move freely in relation to the load-bearing subfloor when the wood shrinks or swells (expands). The "contiguous surface" is achieved by fixing the units together with the help of hangers, locking tongue and groove systems (click systems) or gluing together tongue and groove. Gluing together in tongue and groove cannot normally be used for solid boards and parquet boards. A floating floor is available in many different forms and is very easy to repair.

An intermediate layer is usually inserted between the wooden floor and the subfloor, so that there is certainty that the floor surface can move freely. The intermediate layer can be made of materials that contribute to improving thermal insulation and acoustic properties.

Floating floors can be installed on a load-distributing subfloor of sheet materials or directly on the intermediate layer. The individual wooden floor types each have their own requirements for the stiffness properties of the board layer and the intermediate layer.

Fig. 8: Example of a floating floor

Go through the checklist for "laying non-load-bearing floors", see above, thereby ensuring that the conditions for laying are in place.
Always read the supplier's installation instructions thoroughly. The instructions below are generalized and product-specific deviations may occur.

The first row of boards is laid with the groove side against the wall. The boards are straightened according to a string or a straight line, as the wall itself is rarely straight enough. A minimum of 10 mm of air must be kept to the wall. The distance is best secured by using temporary distance blocks. The boards are assembled by using the factory-made click or bracket system, or by gluing in tongue and groove. Be careful that the boards do not shift during installation and that the end stops are closed. The last board is sawn to length and the "stump" is used as a starting board in the next row. With this technique, the end joints are offset in a "random" joint that most people prefer.

All wooden floors change shape in step with the surroundings. When laying a wooden floor, you must ensure that it can accommodate the movements that changes in humidity will cause. To control this, above the floor surface, a 10-board measure is often used. The 10-board measurement indicates the width 10 boards are expected to have in the most humid state of use. In the case of floating floors laid as "click floors" or in braces, the floor installer has no opportunity to influence the 10-board measure. Swimming floors that are glued in tongue and groove can be joined closer or looser. In such cases, the floor installer must pay particular attention to complying with the supplier's instructions regarding the 10-board measure.

In order for the floors to lie neatly all year round, expansion joints must be made along the walls, etc. The general guideline is 10 mm air for all fixed restrictions. But the recommendations depend on the type of wood used. In large rooms, it may be necessary to divide the floor surface by making expansion joints in the floor surface. The general rule for floating floors is that if the width of the floor surface exceeds 8 metres, an expansion joint should be made. The floors move considerably less in the longitudinal direction, and expansion joints across the direction of laying are often unnecessary. The general guideline is that the length of the floor surface must exceed 12 meters before expansion joints to accommodate longitudinal movements are necessary.

Large mechanical loads, e.g. from large racks, point loads, counters, etc., can hinder the floor's ability to move. Likewise, an irregular geometry, as well as columns etc. hinder the floor's freedom of movement. In these cases, it is also recommended to carry out expansion joints.
If there are expansion joints in the subfloor, these MUST be continued up through the floor covering.

Deflection and flatness of floating wooden floors.
The flatness of floating wooden floors is measured in an unloaded state. The requirements for flatness should be agreed or specified in the tender documents. If nothing has been agreed, a tolerance of +/- 2 mm, measured over a 2 meter straight beam, will normally be acceptable, see the flatness and floors section for further information on measuring flatness. Floating floors can bend under load due to flexibility in the underlay mats and inaccuracies in the subfloor. If a client has specific requirements for this area, they must appear in the tender material / basis of agreement. If nothing has been agreed, a deflection of up to 2 mm will normally be considered permissible. The deflection is measured by loading the floor (with a point load). If you bend the floor, measure the depth of the bend with a 2 meter straightedge as a reference, see also the illustration below.

1.7.4.3 Nailed and screwed floors

Wooden floors on load-bearing sub-floors can be attached to the sub-floor with nails or screws. The method is mostly used in older buildings and is only rarely used in modern floors. For additions to and repairs to floors laid using these techniques, it is recommended to continue with the originally used installation technique. The subfloor must be thick enough to ensure satisfactory retention of the nail or screw. There are two main principles that apply. Concealed nailing/screwing or nailing/screwing from above, these are illustrated in figures 10 and 11 (nails can be replaced with screws).

Fig. 10: Floor board nailed from above and covered

The choice of nail type depends on the type of wood used and the type of floor. As a general rule, square nails for hand nailing and spiral nails for machine nailing are used for soft wood species, such as pine and spruce. For hard wood species, such as oak and beech, divers are used for hand nailing and T-nails, spiral nails and staples for machine nailing. Nailing should be done with hot-dip galvanized nails, which according to experience have the best pull-out value. At the same time, unlike bare nails, there is no contamination from hot-dip galvanized nails, which means that the risk of leaving marks on light, delicate boards is reduced.

The choice of screw type depends on whether you are screwing vertically from above or from behind. For screwing vertically from above, Ø 5 mm self-tapping screws with partial thread are used. These are screws with a smooth threadless shank just below the head. They ensure a better tightening of the board to the substrate than screws with full thread. For concealed screwing, special screws such as Monta-flex are used, which give a high pull-out value in wood, wood panel and concrete substrates.
When screwing from above, pre-drilling is recommended. As well as countersinking with a larger diameter to make room for the screw head (dimension 6 mm deep hole diameter Ø10 or Ø15 mm). The holes are then covered with a wooden plug, which has been drilled out of cut-off board scraps with a plug drill.

Fig. 11: Floorboard screwed and plugged

Shown below are a number of examples of nails and screws that can be used for floor mounting.

The plugs are glued with the veins in the same direction as on the boards. When the glue is dry, the plug is removed and the upper side of the board is sanded smooth.
In the following table is an overview of which nail types and dimensions are recommended for different combinations of subfloors and wooden floors.

See also the method description under floating floors for further information on installation.

1.7.4.4 Fully glued wooden floors

Fully glued wooden floors are understood to mean wooden floors that are glued to the subfloor over the entire surface. There are a number of conditions that must be in place to get a good result.

When fully gluing wooden floors, the substrate must be flat - i.e. with deviations of no more than ± 2 mm in 2 m - and without burrs and ridges to ensure proper contact between the materials. Wooden floors must not normally be glued before:
• The residual pore moisture in the substrate is below 65% RH measured at temperatures between 17 and 25°C, or
• an effective moisture barrier has been installed.

The general recommendation is that a water-free parquet glue such as an MS glue, which is available in a number of manufacturers, is used for fully glued wooden floors. If glue based on polyurethanes is used, you must be aware that this type of glue requires a number of work environment measures. The adhesive surfaces must be clean, dry and adhesive and the supplier's instructions regarding priming, adhesive consumption, application method, installation time and load requirements must be observed to ensure a good result. The floor materials must not be windward and must have a flat underside that ensures a good adhesive surface.

The substrate must be level with deviations of no more than ± 2 mm on 2 m (± 0.6 mm on 0.25 m). There must be no burrs or ridges that could prevent proper contact between the wooden floor and the substrate. The tensile strength of the substrate must be agreed with the supplier. In addition, it is recommended that you check that the surface is not weak or muddy. The residual building moisture in the substrate must normally be below 65% RH at a temperature between 17 and 25°C, or an effective moisture barrier must be installed which can prevent moisture from the substrate from penetrating into the wooden floor.

If an adhesive with moisture-retarding properties is used in the quantity prescribed by the supplier, wooden floors can, however, in some cases be glued to concrete substrates with a pore moisture content of up to 85% RH without the use of a moisture barrier. The fact that an adhesive has moisture-retarding properties must not be confused with the fact that it has moisture-blocking properties. In surface-treated floorboards, there is therefore a risk that moisture from below, which penetrates through the glue, may give the boards a slight transverse curvature (washboard effect), which should, however, always be assessed from normal standing height. However, the wooden floor supplier's instructions must always be followed.

Glued wooden floors emit less drum noise than, for example, floating wooden floors. However, the type of glue has no significant effect on the drum sound level. The fact that a wooden floor is fully glued does not mean that the glue is 100% covering. Smaller areas without glue can be observed by sound differences when the floor is stepped on or tapped on. Smaller areas, without glue, usually have no effect on the floor's functionality and lifespan. If the fully glued wooden floor is otherwise functional, "hollow sound" to a lesser extent must be expected and accepted. A smaller scale means up to 10% of the floor area. However, any "hollow" areas must be evenly distributed. It is emphasized, however, that there must be no staves/units that are decidedly loose.

Laying glued wooden floors.
Go through the checklist for "laying non-load-bearing floors", see above, thereby ensuring that the conditions for laying are in place. Always read the supplier's installation instructions thoroughly. The instructions below are generalized and product-specific deviations may occur.
With glued wooden floors, the start-up is extremely important. For most floor types, it is advantageous to start by placing an exit row in the middle of the room. If the floor (in the lengthwise direction) is to be brought in unbroken through one or more doors, the exit row can advantageously be laid in through the door openings. The escape of the output row is best ensured by creating this along a string. When the starting row has been laid, it is recommended that you do not continue working until the glue has hardened. The floor is then laid. The application of glue can be done manually with a notched trowel or with machine application. The amount of glue must be adapted to the product and the conditions. Reference is made to data sheets from the suppliers.

Glue machines must be advanced at a uniform and correct speed, otherwise the amount of glue (l/m2) will not be correct. The quantity is best controlled by installing completely new glue bags in the machine. The total contents of the bags are determined and it is calculated how large an area a full machine must be able to cover. The area is marked on the floor and a test laying is carried out. By comparing the laid area with the "expected" area, it can be determined whether the laying speed is correct. The floor surfaces should be loaded until the glue has hardened. Be aware that the glue is all the way to the edge.

Spacers and 10-board measurements
In order to ensure that the floors lie neatly throughout the year, it must be ensured that the floors' 10-board measure is observed. With glued floors, this is best done by using the so-called spacers. Spacers are small plastic pieces that are placed between the rods. This ensures a uniform joint distance between the rods. The principle behind the use of the spacers is to give the rod room to work freely over its own axis without pushing the neighboring rod. Long restrictions end with approx. 10 mm joint. By using spacers, expansion joints in the traditional sense can be dispensed with and a glued wooden floor can in theory be made "infinitely" large.

However, the spacer technology requires that the rods have a uniform width and a uniform moisture content upon delivery, and that they remain in airtight packaging until shortly before the laying time. Correctly laid poles will, in the summer when the moisture content of the air is at its highest, lie completely close. At the end of winter, when the humidity is at its minimum, there will be small uniform joints between the sticks. Read more about laying tiled floors using spacers under "Laying wooden floors using spacers"

1.7.4.5 Wooden floors and soundproofing

Sound deadening of a floor structure is a complex area that is affected by all the "components" that make up the structure. It is possible to improve the acoustic properties of wooden floors by laying out an acoustic underlay - a footfall sound dampening sound mat - under the floor surface or, for screed floors, using sound tiles under the tiles. With floating floors, the acoustic underlay is usually laid loosely under the floor. With glued wooden floors, the acoustic underlay must be glued to the subfloor and the wooden floor must be glued to the acoustic underlay. Most acoustic surfaces are reminiscent of vinyl/rubber track material. These types of products are usually glued with acrylic dispersion adhesives, but they can be glued with an MS adhesive. However, one must be aware of a number of conditions in this connection.

MS adhesives generally cut worse than acrylic dispersion adhesives. When laying out acoustic substrates (sound mats) on larger areas, it is necessary to drum the substrate to ensure correct glue spread. If an MS adhesive is used, the risk of the substrate bulging will be far greater than it will be if an acrylic dispersion adhesive is used. From a purely gluing technical point of view, an acrylic dispersion adhesive can be used, but there are also some factors regarding sound attenuation that should be considered.

MS adhesives are generally assessed to have greater impact sound insulation than acrylic dispersion adhesives. And if the floor structure has been acoustically tested and approved, you must be extremely careful when substituting one element with another element. You risk changing (a lot) the values. Glue method and product selection should always be stated in the construction case description. If the construction case description does not specify which type of glue is to be used, the committee recommends that you consult the supplier of the acoustic mat and use the glue recommended by the supplier.