When it comes to stone and tiles for walls or flooring, a proper grout joint is an important part of the specification. While many architects and designers like the idea of a thinner grout joint for aesthetic and maintenance purposes, it's important to understand why a thicker grout joint may be better.

What is a grout joint

A joint is an expansion joints or they can also be called movement joints or movement accommodation joints. In ceramic, porcelain and glass and stone tile installations, they are critical to the success and durability of any installation. 

Benefits of a proper grout joint

1.) Reduce the likelihood that tiles will chip if/when the subfloor moves.
2.) Minimize the appearance of inconsistencies in tile.
3.) Minimize the likelihood that the tile pattern will be thrown off upon installation.

Tile grout joints are critical because without them, particularly on floors, most installations that appear to be well done will eventually fail. This will of course be subject to sunlight, temperature, adhesive used and the condition of the substrate. 

If tiles in certain applications do not have enough room to expand, they may pop up or "tent" in the middle of the floor. See below image example. These situations can occur in both residential and commercial applications. ​

What grout joint should I use?

Tile Size
Larger tile formats tend to create more lippage when installed, or unevenness in the surface depending on the quality of the tile manufactured. This means thicker grout joints may be necessary.

Tile Variation (Differences in Size)
Pressed edge, cushion edge or rolled edge tiles can differ in thickness and tile size. Your grout joints must accommodate for these possible irregular sizes for this to achieve symmetry and the straightest lines possible. Australian standards for tile manufacture allow for size variation within batches and your grout joints need to be thick enough to accommodate this variation. Speak to your tiler for the best possible solution.

The Plane or Surface
Grout joints can accommodate for differences in the angle of the surface (i.e the fall of a bathroom floor or where the floor or wall is not level). As the plane/angle of the tile changes the grout joint will assist in providing a smooth continuous slope from one tile to the next. Although grout joints done properly can accommodate minor or subtle changes in surface variation, surface leveling is always recommended. 

​Grout joints are known to absorb or take up strain from the various stresses imposed in tile installations and if this relief is reduced by the reduction of joints as occurs with large format tiles, there is a greater need for wider or more closely spaced movement joints. For more information on movement joints please refer to AS3958.1 and 2.

What causes movement of tiles?

Damage to grout joints can occur for a number of reasons. It is always recommended that flexible adhesives and appropriate control joints to the size and type of tiles be specified. 
​
Physical movement of the building itself
Stress and damage can be caused to any control joints if there is any settlement of a fixed a structure, vibration or deflection to the surface that the tiles are fixed too. It does not make a difference if you have installed ceramic or porcelain tiles, if there is movement in the substrate and there is no space for the tiles to move into, then there will be some sort of damage transferred through the installation. 

Thermal fluctuation
Changes in the ambient temperature of the environment where tiles are installed can lead to movement in the substrate adhesive and the grout joints. It has been documented that areas in which there are large glass windows where exposure to hours of hot sunshine will have the effect of causing failure to the bond between the tiles and the substrate due to thermal expansion. This is more evident in outdoor areas where tiles and substrates will adopt the thermal temperature of its surroundings and can suddenly drop in a matter of seconds due to a sudden rain shower. 

It is important to consider that the thermal properties of the tiles installed, the type of adhesive and the substrate will all expand and contract in different temperatures and rates. Always ensure appropriate adhesive types, grout types and additives are specified for installation. 

Expansion and shrinkage of substate
When concrete is poured and it cures, it loses a percentage of its water content. It is critical to allow the concrete to settle before applying tiles. The shrinkage can cause complete failure of the tiles, usually in the form of cracks as the substrate contracts and moves. 

Likewise, when moisture reaches the substrate it will result in a change of shape and size which will ultimately lead to movement of the control joints and tiles with similar consequences. It is critical that proper waterproofing and sealing occurs in areas subject to possible moisture. 

AS3958.1 2007 5.4.6 Tile finish and joints
The Australian Standards as of 20 February 2018 only refer to and establish standards and tolerances for non rectified or pressed edge/cushion edge/ rolled edge tiles. 

​​The recommendations for tile finish and joints are as follows:

1. When measured with a straightedge, the finish surface of the tiling should be flat and true to within tolerance of ±4 mm in 2 m from the required plane. The lippage between two adjacent tiles should not exceed 2 mm. In the case of tiles where the surface has been ground flat, for example polished tiles, the lippage should not exceed 1.5mm, and for joint widths of 3.0 mm or less the lippage should not exceed 1.00 mm.

NOTE: Lippage is inherent in all installation methods and may also be unavoidable due to the tile tolerances. Lippage may also be unavoidable where tiles larger than 150 x 150 mm are graded to a waste outlet, unless transverse cuts are incorporated.

Any adjustments of tiles should be made before the initial set of the bedding material takes place.

1. In readiness for grouting, any surplus bedding material remaining on the surface of the tiles or in the joints spaces should be removed before it hardens. Care should be taken to avoid disturbance of the tiles during the setting of the bedding.
2. Joint widths should be consistent throughout the installation unless otherwise specified. The recommended joint widths are as follows:

(i) floors:
                    (A) Dust-pressed tiles ………………………………………….3 mm
                    (B) Extruded tiles ………………………………………………..6 mm
(ii) Walls:
                     (A) Dust-pressed tiles ………………………………………1.5 mm
                     (B) Extruded tiles ………………………………………………..6 mm

Wider joints may be required to accommodate larger tiles, dimensional irregularities in the tiles, to maintain modular discipline, or to provide a decorative effect. Where larger format tiles are laid using narrower grout joints, movement joints should be placed at closer centres.

Joint widths are normally measured at the tile face.

When spacer lug and universal edge tiles are used, the tiles automatically provide suitable spacing, approximately 1 mm to 2 mm for walls and 3 mm to 6 mm for floors.

1.  Joint alignment should be consistent throughout the installation unless otherwise specified. The final alignment should be within a tolerance of ±4 mm in 2 m from the specified joint alignment. Provision should, however, be made for variation in the type, size and quality of the tile.
2. When tiles without spacer lugs are used, the correct spacing should be obtained by using spacing inserts of suitable thickness between the tiles as fixing proceeds. Tiles without spacer lugs should never be fixed butt joints, as an adequate width of joint is necessary for the relief of any local stress.

Spacing inserts should be removed in conjunction with the preparation for grouting.

NOTE: This is particularly important in larger areas of tiling, in high-rise structures and in wide span post-tensioned concrete floor systems. Rigid spacing inserts left in place may negate the contribution of grouted joints to the relief of irreversible differential movements.