Terrace, balcony or garden can be tastefully decorated with tiles in various styles according to individual preferences. However, the requirements are much higher outdoors than indoors. In this article you will find out which requirements tiles must fulfil in order to be able to exist permanently as floor coverings outdoors and what you should absolutely observe when laying them.
Possible applications of tiles: Exterior vs. interior
From small to large, from light to dark, from natural stone to wood look – tiles are available in the most diverse formats, colours and designs. Coupled with their advantageous properties in terms of comfort, durability and cleaning, this results in almost unlimited application possibilities. No wonder, then, that tiles are both popular and widespread as floor coverings not only indoors but also outdoors.
However, the conditions outside are completely different from those in enclosed living spaces. The ground is exposed to the weather all year round and the interplay of sun, rain, ice and snow demands a lot from the material. In order for the flooring to be able to withstand outdoor use for a long time, tiles must therefore be particularly robust and resistant to external influences and stress.
Which tiles are suitable for outdoor use?
In order to ensure that the tiles are able to withstand the daily stresses and strains on the terrace, balcony or garden, the following criteria should be taken into account when selecting the tiles:
Weather resistance and frost resistance
The most important criterion for outdoor tiles is that they are weatherproof. Thus, the material must not only be able to withstand the heat of direct sunlight in summer, but above all the cold and frost in winter.
Decisive for the frost resistance is the water absorption capacity. The rule is: the less, the more frost-resistant. If too much water penetrates into tiles and joints due to humidity or precipitation and expands in the cold, there is a risk of cracks, flaking or efflorescence.
In principle, a porous surface absorbs more water than a fine-pored one. For this reason, pure stoneware is generally not recommended for outdoor use due to its nature. Ceramic tiles made of stoneware or porcelain stoneware, but also natural stone (e.g. granite) or terracotta can very well be used outside, provided that they are approved for this purpose according to the information provided by the tile manufacturer.
The decisive factor for the degree of frost resistance is the classification, according to which the tiles are divided into the following five groups based on their water absorption capacity:
Group Ia: < 0,5 % water absorption capacity
Group Ib: < 3 % water absorption capacity
Group IIa: 3 to 6 % Water absorption capacity
Group IIb: 6 to 10 % water absorption capacity
Group III: > 10 % water absorption capacity
Group Ia and Ib tiles – i.e. up to a maximum water absorption capacity of 3 percent – are generally considered frost-proof. They are additionally marked with a blue ice crystal as a symbol and can be laid outdoors without hesitation. To be on the safe side, a tile with a water absorption capacity of less than 0.5 percent should be preferred in the best case.
In contrast, there is already a considerable risk of frost damage in groups IIa and IIb – and group III is not advisable for outdoor areas if the flooring is to survive the winter without damage.
Another selection criterion for exterior tiles is abrasion resistance. It determines the stress the surface is suitable for without signs of wear and tear.
This is divided into 5 tiles abrasion groups:
Abrasion group 1: Very light duty
Abrasion group 2: Light duty
Abrasion group 3: Medium stress
Abrasion group 4: Heavy duty
Abrasion group 5: Very heavy duty
Basically nothing can go wrong with unglazed tiles in outdoor areas – they can always be assigned to the highest abrasion class. The hardness of the surface is comparable to that of diamonds, making them virtually indestructible even under extreme stress.
With glazed tiles, on the other hand, things look slightly different. Depending on the type and design of the glaze as well as the degree of wear and tear and soiling, visible signs of use are quite possible over time. Therefore, glazed tiles on the balcony should have at least abrasion class 3, for use on terraces or in the garden, abrasion class 4 is even more recommended.
Last but not least, special attention should also be paid to slip resistance in the case of exterior tiles. This is because wet or damp tiles can quickly become slippery and cause nasty falls or injuries.
The slip resistance can be recognised by the skid resistance classes, into which tiles are divided depending on their static friction value:
R9: low coefficient of static friction, safe to step on at an angle of inclination of 6 – 10°
R10: normal coefficient of static friction, safe to step on at an angle of inclination of 11 – 19°
R11: increased coefficient of static friction, safe to step on at an angle of inclination of 20 – 27°
R12: high coefficient of static friction, safe to step on at an angle of inclination of 28 – 35
R13: very high coefficient of static friction, safe to step on at an angle of inclination of over 35
In outdoor areas, at least R10 should be selected, and R11 ensures even better slip resistance if there is a particular risk of slipping (e.g. on stairs). In areas that are also frequently walked on barefoot (e.g. in and around the pool or in the garden shower), attention should also be paid to the additional “B” or “C” marking for suitability in wet barefoot areas.
Unglazed tiles also offer a certain advantage in terms of slip resistance in outdoor areas. Thanks to their rough surface, they are naturally more slip-resistant. Even small tile formats can additionally increase the slip resistance due to the significantly larger joint proportion.
Garden, balcony and terrace: Choose the right tiles for the outdoor area
When choosing tiles for the terrace, balcony or garden, it is therefore advisable to always opt for the higher quality class. This may have an overall impact on the price, but the extra cost is worth it simply because of the longer life of the floor tiles.
Which exterior tiles are ultimately best depends primarily on personal preferences and the style of the house. Floor tiles for outside as well as for inside are available in the most diverse surfaces (e.g. unglazed, glazed, matt, silk matt, high gloss etc.), optics (e.g. wood optics, natural stone optics, marble optics etc.), formats (e.g. square, rectangular) and colours.
What should be taken into account when laying outdoors?
However, the decision for the right exterior tiles is only half the battle. Even the best flooring can be damaged – usually by water – if the tiles are not laid properly.
Therefore, outdoor installation should be carried out with great care, taking into account the following factors:
Prepare the substrate
The substrate for exterior tiles must be load-bearing, frost-resistant and completely even. Concrete slabs or a cement screed reinforced with construction steel mats on a compacted and sufficiently drained layer of gravel or crushed stone are most suitable.
A gradient of 2 per cent must be observed so that water can quickly drain away from the tiles to the outside. In order to protect the tiled floor from moisture even from below, the substructure should also be sealed (e.g. with bitumen coating or sealing slurry and double-layer PE foil). In addition, the surface should be carefully checked again for cracks, unevenness or any residue from removed flooring before installation and repaired if necessary.
The right laying material
When laying outdoors, only flexible tile mortars or adhesives should be used to reduce stresses on the floor surface and thus prevent cracks or fissures in the tiles.
Laying tiles correctly
When laying the tiles themselves, it is important to avoid cavities between the substrate and the tiles in order to prevent water inclusions. This is best achieved with the so-called buttering-floating process, in which the tile mortar or adhesive is applied both to the substrate and to the back of the laid tile. Alternatively, thin-bed installation can be used, in which the tiles are pressed in sections directly into the damp fluidised bed mortar or tile adhesive.
In the edge areas, it is essential to ensure that the necessary expansion joints are provided in order to give the floor the necessary scope for temperature-related expansion and thus avoid stresses. It is also important that the tile adhesive is allowed to harden (approx. 48 hours) before grouting is started.
Carefully grouting tiles
Leaky joints are often the Achilles’ heel of exterior tiles. They can easily allow moisture to penetrate and cause damage to the substructure, the tile mortar or the tiles themselves. Therefore, special care and precision is required when grouting in outdoor areas.
In order to be able to work as precisely as possible, the joint sealing compound should be applied to the gaps diagonally to the joint line with a rubber wiper. Excess grout can be removed with a sponge board after approx. 15 minutes of drying. In the last step, the expansion joints and other transitions can then be sealed with silicone.
ATTENTION: The surface can only be walked on and loaded when the tile mortar or adhesive has completely hardened. This phase can take different lengths of time depending on the product, so it is essential to follow the manufacturer’s instructions. During the drying phase, excessive humidity and direct sunlight should be avoided.