Fact sheet
7 - 2012

Changes in part N – Brick and tile work.
Part 1: Tile work

By Senior Researcher Arne Nesje, SINTEF and José Delgado, Standard Norge.
Commissioned by the Norwegian Building Ceramics Association.

The NS 3420 «Descriptive standard for building, construction and installation» is used to develop descriptions for inquiries, cost estimations, and follow-up of building projects. Significant changes have been added to the part on brick and tile work. In two articles we will describe some of the changes and clarifications that have been made in the 2012 version. This article talks about tile work in general, #8 will talk about complex tile constructions.

Figure 1: NS 3420 in a new version after 2008

Part 1: Joint provisions. Tolerance requirements and joint width

Tolerances for builiding can now be found in NS 3420 part 1, that talks about joint provisions for all the trades. Surface divergences and tolerance measurements on finished tile work provides clear guidelines. Subsection 4, d) in Joint provisions has tables that show which tolerances are applicable, and how to measure divergence. Table 1 in figure 3 shows the current tolerance requirements. Table 3 in the same figure shows the flatness tolerances divided into classes. For instance, a tiled floor must meet the requirements of flatness of tolerance class PB.

Figure 2: Local flatness applies to depressions and bulges over a given length, and is measured with a floating rule.
Figure 3: Classification of the flatness tolerance can be found in the joint provsions, table 1 and 3 In NS 3420 part 1.

Table 1 – Normal requirements for tolerances of surfaces in and on finished buildings

Type of
Outer wall
Inner wall
Outer roof
Stairs, balconies
Outs. cladding,
Inside cladding.,




Table 3 – Flatness tolerance classes for buildings.

Type of flatness
Unit of measurement
Tolerance class
Local flatness 2,0 ± 2mm ± 3mm ± 5mm ± 8mm
1,0 ± 1mm ± 2mm ± 3mm ± 5mm
0,25 - ± 1mm ± 2mm ± 3mm
Total flatness Entire product ± 5mm ± 10mm ± 15mm ± 25mm
Height difference - 0,5mm 1mm 2mm 4mm
Figure 4: Part 1, subsection B5 in addition to B describe the measurement technique for controlling local and total flatness tolerances.

The standard part 1 subsection 4, e2) describes that tolerances for your own work must always be controlled and documented before following work is started. Depressions and bulges on surfaces is measured with a floating rule, as shown in figure 2. Divergences in e.g. flatness class PB must be ±3 mm from the middle area. This class is normally used if not otherwise specified.

Part N: Brick and tile work.

The chapter has been changed to provide a clearer divide between the responsibilities of the craftsman and the responsibilities of the builder. Much of the text from the previous version has been kept, but with some edits and rewrites. Subsection NH Tile work describes how to lay tiles on a suitable foundation, e.g. on smooth concrete. It talks about general requirements for choice of tiles, stones and boards.
In the standard there are also an overview of slip resistance classes and areas of use as an informative appendix (appendix A). Grip and tile grout must be according to current standards. The standard now talks about “Complex tile construction” in its own sub-chapter, and we will talk about this in part 2 of the article.

Choose flat tiles in areas with strict requirements for flatness on finished surfaces.

Local flatness divergences due to the production tolerance of the tile type is not considered part of the surface divergence of the tile construction (subsection NH d2) in part N). E.g. large-format tiles or shale with natural flatness may have inherent variations in length, width or thickness that exceed the requirements of the NS 3420. In cases where the builder has strict requirements for surface flatness, you must buy suitable products e.g. rectified tiles, so that there is no discord between production tolerances and planned surface requirements.

Describe and choose suitable tile bonds.

As figure 5 illustrates, curved tiles may cause problems regarding the edges of the joints. Tile bonds must also be planned according to the requirements for surface flatness. Choose stack bonds rather than an offset bond if there are strict requirements for flat surfaces with little height difference in the joints.

Figure 5 a and b: Offset bond may cause undesired height differences between tiles (Illustration: Alt om flislegging).

Requirements for tolerances of joint width.

The width of the joints on a finished surface must not diverge with more than 20% of what is indicated. If you choose tiles with larger tolerance divergences, the tiler may have problems with meeting the requirements. If there are requirements for precise joint widths, you must also select tiles with a precise format.
For mosaic sheets, the distance divergence between each tile must be within ± 20 % of the joint width between each piece on the sheet.

Requirements for execution and gluing method

Under general execution requirements (subsection NH2 c) it says that

"The contact between the adhesive and the foundation, as well as between the adhesive and the tile, must be sufficient in order to endure the strains for which the tiles are specified."

A much-debated topic is how the requirements for glue coverage should be articulated and practiced. It would be optimal if the underside of the tile has complete contact with the glue, something that is difficult to achieve in many cases. The larger the tile, the more difficult it is to achieve complete glue coverage, even though the glue manufacturers have developed new glue types for this purpose. In most cases, sufficient contact between glue and tile is achieved even though there are smaller cavities and grooves in the surface. The surface then fulfils its functions, and does not detach. But for outside constructions and constructions that are subject to a lot of water strain, the standard emphasises the importance of complete glue contact.

c1.5) For outdoor tile constructions and for constructions that are subject to a lot of mechanical or water strain (swimming pools, floors in wet industries and commercial kitchens), the tiler must strive to achieve complete contact between the tile and the adhesive on the entire surface of the tile.

The phrase «strive to achieve complete contact» is used because complete contact, i.e. 100% glue coverage, cannot be set as an absolute requirement. A formulation such as “approximately” complete contact allows for interpretations that cannot be measured. Is e.g. 90% glue contact approximately complete contact? Especially outdoor constructions must have glue layers with no cavities, as well as good contact and cooperation. In order to meet the intentions of the standard, suitable materials must be used, and the tiler must use suitable methods and strive to achieve complete coverage. The tiler must do that little extra something in order to achieve this. This includes controlling his own work by performing a “butcher’s test”.

Figure 6: The «butcher’s test» can be used to see if complete contact between glue and tile has been achieved.

Description of general tile laying

One of the points in the standard talks about tiling of surfaces (as shown in figure 7), and it describes the building component, tile, adhesive and tile grout as well as foundation and adhesive technique. Materials and execution are unambiguously described.

y1) Code specification
Area [m2] Building component: {Matrix NH:1}
Exposure: {Matrix N:2}
Tile: {Matrix NH2:1}
Adhesive technique: {Matrix NH2.1:1}
Localisation: (part 1, 4, y5)
Foundation: (NH, y2.2)
Type of tile: (NH,y2.3)
The total thikness of the tile layer:
Adhesive: (NH, y2.4)
Tiel grout: (NH, y2.5)
Joint width:
Other requirements: (NH, y2.6; NH2.1, y2.3) Yes No

Figure 7: One of the code specifications of the standard

The standard has now specified through the matrix on figure 8 which glue category and glue technique that should be used.

Number in the codeAdhesive technique
0 Optional
1 One-sided application
2 Buttering floating
3 Liquid glue
4 Glue mortar (thick setting glue)
5 Setting mortar
6 Mechanical
9 Other method - must be specified
Figure 8: y2) describes which codes can be used in order to determine adhesive type and method.

Figure 8: y2) describes which codes can be used in order to determine adhesive type and method.

Tile and mosaic work are diverse, and there are details that cannot be described in the general posts concerning flat surfaces. Therefore, there are now specific posts for:

  • Trimmings and parts of decorative tiles (NH2.3)
  • Tiled marking areas and lines (NH2.5)
  • Mounting units in the tile layer (grates, valves, grooves) (NH6)
  • Additional costs when adjusting to completion and adjusting to connections (NH8.1 and NH8.3)
  • Uncoupling layer (NH8.5)
Figure 9 a, b and c: Example of tiling of uncovering and side slopes (a), adjustment to an exterior corner (b) and a tile construction with an uncoupling layer (c).

Some general recommendations in the standard

Think symmetry

c1.1) If there are no detailed drawings that indicate the placement of the tiles, the tiles should, as far as possible, be placed symmetrically on the foundation and symmetrically in relation to larger openings.

Additionally, professional tile work requires planning the execution so that adjustment tiles in corners and edges are not smaller than half a tile.

Figure 10a and b: Example of correct (a) and wrong (b) distribution of tiled surface

Strive to achieve complete glue coverage (c1.5)

Especially for outside use, glue should be applied to both the tile and the foundation (number code 2 on figure 7) On large-format tiles indoors it may also be beneficial to use buttering-floating.

Figure 11: Complete glue coverage can be achieved when planning which materials and methods to use well beforehand

Summary part 1

The purpose of using NS 3420 is to make descriptions that are as unambiguous as possible, so that they constitute the basis for the best possible cost estimations.
The part N: 2012 version of NS 3420 has undergone several changes, such as clearer divisions between requirements for descriptions and execution. This article has discussed requirements such as tolerances, gluing techniques and general material requirements for tiles attached to treated foundations. Part 2 of this article (NBKF # 8/2012) describes complex tile constructions.

Sources and references.

  • NS 3420-1: 2012 Joint provisions
  • NS 3420-N: 2012 Brick and tile work
  • The book Alt om flislegging, SINTEF Byggforsk and BKF, 2011

Images are borrowed from the BKF archive.
Sketches and illustrations from Standard Norge and Alt om flislegging.