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

2.2.0.1 General
Gluing is used so that the floor covering must lie firmly against the subfloor, so that it does not shift or bulge.
Gluing has a great influence on how a floor covering is able to withstand impacts, e.g. from walking to rolling traffic and/or from moisture-related movements. Correctly executed gluing gives the floor the longest lifespan.
Floor glues are special glues that have been developed for specific purposes. Most conditions when using floor adhesives are very similar, but there are differences. To achieve a good result, both the floor covering and the substrate must be taken into account.
Glue must be chosen in consultation with the flooring supplier so that it fits the task at hand, i.e. floor material, substrate and load.

Most floor adhesives today are water-based, and as a general rule, they have only achieved their strength when the water has evaporated. If the floor covering is permeable to water, such as in connection with cleaning, both the adhesive and the substrate must be able to withstand short-term exposure to moisture.
For gluing under difficult conditions, 1- or 2-component glue without water may be used. The use of these types of glue can, however, cause a number of work environment problems, as the binder is usually based on polyurethane. In these cases, the rules of the Norwegian Working Environment Authority must be followed.
In order to achieve the best possible adhesion, the glue and coating supplier prescribes an amount of glue per square meters. However, the amount of glue is only indicative, as the flatness and absorbency of the substrate have a large influence on the need for glue.

From a technical point of view, glue should:
• Have sufficient strength to withstand the forces that occur in the glue joint
• Be able to withstand the influence of moisture up to the specified value
• Have the ability to stand in glue strings, so that contact can be made between glue and floor material
• Have a low water content to avoid deformation of the floor materials due to one-sided water impact on the underside of the floor covering
• Not have annoying off-gassing to the indoor climate
• For use with certain floor coverings be resistant to softeners
• Meet authority requirements for environmental labeling and safety data sheets
• Have quick fixing so that the coating is retained in the glue joint

2.2.0.2 Bonding methods
There are four main types of bonding:
• Wet gluing, including late wet gluing
• Staple gluing
• Contact bonding
• Dry gluing

Wet gluing
With wet gluing, the substrate and coating are brought into contact with each other as soon as possible after the glue has been applied.
The advantages of wet gluing are that good strength can be achieved and that the floor covering can be adjusted after laying.
Plastering the substrate is used, among other things, to achieve sufficient absorbency for the glue.
Wet bonding is used where the substrate or coating is often absorbent and usually for wooden floors and elastic floor coverings.
Late wet gluing
Certain floor covering types require late wet gluing to avoid dimensional changes due to the influence of moisture from the glue. By late wet gluing, it is understood that the laying is only carried out when the majority of the water has evaporated, but that there is still an opportunity to adjust the floor covering and at the same time achieve good strength.
Late wet gluing is used i.a. for less absorbent substrates or for special situations, such as when walls and ceilings in laboratory environments are to be covered with elastic floor coverings.
Staple gluing
Only suitable types of glue should be used for adhesive bonding.
With adhesive bonding, the surfaces are only brought into contact with each other when the glue has achieved a "tape effect", which is checked by pressing with a finger on the glue string, which must not cause contamination.
Adhesive bonding is primarily used where neither the coating nor the substrate is absorbent. The contact between material and glue is hardly as good as it is with wet gluing. Adjustment of the coating after laying down is not possible.
Adhesive bonding is normally used for textile floor coverings, but is also used for certain types of elastic floor coverings such as vinyl tiles.
Contact bonding
For contact bonding, glue is applied to both surfaces. The glue must be dry before the surfaces are brought into contact with each other with the greatest possible pressure. There is no possibility of subsequent correction of the location of the floor covering on the substrate.
Contact bonding is normally only used where other options for bonding cannot be used.
Dry gluing
Dry gluing is done with foils with a double-sided adhesive layer.
Foils are available in different widths. Foils for full-surface gluing on floors are usually from 50-100 cm wide and strips are available in different widths depending on the intended use.
Strips are normally used for baseboards etc. but can also, for example, be used for gluing hulkehl in and outside wet rooms.
Dry bonding can be used on both absorbent and non-absorbent substrates and it is normally required that the substrate be primed.
Dry bonding is only suitable for textiles and elastic floor coverings. There is no drying time, so the floor covering is immediately ready for loading and for possible welding and grouting work.

2.2.0.3 Bonding
When gluing, the adhesive surfaces must be clean, dry and adhesive. The supplier's instructions on glue consumption, application method, etc. must be followed to ensure a good result.
Pay particular attention that you use the correct glue trowel and that some glue trowels must be held vertically to give the correct amount of glue, while others must form an angle of approx. 60º in relation to the floor surface, and that your glue screed is kept clean and free of old dried glue.
When gluing on a concrete substrate, the glue must be able to withstand the remaining concrete moisture, which is approved in relation to the current floor covering type.
Certain types of glue can also be applied with a roller or glue gun / glue machine.

Floor covering type Requirements
Textile or quartz vinyl
Residual building moisture maximum 90% RH
Elastic e.g. linoleum, vinyl, LVT,
cork or rubber Residual building moisture maximum 85% RH
Wooden floors
Residual building moisture maximum 65% RH
Residual building moisture > 65% RH, contact the adhesive supplier

Table 1. Maximum residual construction moisture in concrete when gluing different floor covering types.

Please note that high RF values - typically above approx. 65% RH - in older subfloors, may be due to external moisture. The supplier should be contacted here.

If the residual building moisture of the concrete is higher than the maximum moisture limits, drying must take place or an effective moisture barrier must be built in between the subfloor and the floor covering.
As a starting point, it is never recommended to continue the floor work if the moisture levels are above the requirements for what the adhesives can temporarily withstand from residual construction moisture - regardless of the moisture barrier method.
During and after gluing floor coverings, the temperature in the air and subfloor must be between 17 and 25º C and the humidity between 35 and 75% RH, for wooden floors however between 30 and 65% RH. If the work is to be carried out in other climatic conditions, both the glue supplier and the flooring supplier must be consulted and their instructions must be followed.
The substrate must be uniform and level to ensure the best possible adhesion and strength between the subfloor and the floor covering.
Strongly absorbent subfloors can be primed before gluing to ensure uniform adhesion, in these cases the glue supplier should be contacted.

On gypsum-based subfloors such as Anhydrit, a primer must be used which, in addition to ensuring good adhesion, can also prevent the moisture in the glue from damaging the substrate.
Floor coverings are fully glued to the subfloor with an adhesive according to the flooring supplier's instructions. After laying, there should be no traffic on the floor other than normal foot traffic until the glue has hardened.
All other loads on the floor, e.g. from rolling scaffolds, transport vehicles, furniture or other point loads and the like, must not be applied until the glue has reached full strength at the earliest.
Depending on the temperature and humidity of the room, this takes at least 8 days, but it can take up to 14 days before full adhesive strength is achieved.
Joints in vinyl must not be welded, and linoleum and rubber must not be threaded until the glue has achieved sufficient strength. If glue is applied to a sound-absorbing substrate such as cork or similar, the curing time can be significantly extended.

2.2.0.4 Working environment
Floor adhesive must be marked with a MAL code, which is an expression of the precautions to be taken when working with the adhesive. If there is an adhesive with a lower MAL code than the original product and the desired technical properties are present, this must be selected.
The safety data sheet from the supplier must be at the point of use. In particular, carefully read the points on protective equipment, restrictions on use and any training requirements.
The glue supplier should always be contacted if there is any doubt.

2.2.0.5 Classification of glue
The flooring industry's glue suppliers must comply with the minimum requirements below:
• Shear strength
• Long-term shear strength
• Peel strength
• Softening resistance

Table 2 shows the limit / minimum values that the adhesives must comply with in order to achieve the classification. The documentation is done by presenting test results which show that the glue complies with set criteria.

The Nordtest methods NT 141, NT 142, NT 143 and NT 146 or DS/EN 1902, DS/EN 1372 and DS/EN 1373 are used for the test

Table 2. Basis for the floor industry's classification of floor adhesives for wet bonding.

* Or 100% carpet breakage.
** Heavy load and possibly high water load.