Lay terrace slabs: on earth, sand, grit or concrete?

Building a house and landscaping are expensive affairs. But does every action really have to be carried out by professionals? Laying out a flat surface with terrace slabs is certainly something that even a skilled hobbyist can do! But what seems simple at first glance should not be lightly underestimated. For example, if the subsoil is not right, the terrace slabs sink quickly. But which material can support the panels permanently?

The goal: a beautiful terrace over the long term

The terrace is often the family's "living room" in summer. Many happy hours are spent on it year after year: people eat, play and relax. Accordingly, it should be designed to be inviting and stay that way for as long as possible. If the terrace is freshly built, that's not a problem either. Every record is still in place, nothing disturbs the harmony. But as time goes on, unsightly and unwanted changes can appear:

• Plates sag and lie unevenly
• Terrace slabs no longer look attractive
• cracks appear
• Moss grows between the plates

It is therefore important to prevent these changes effectively even when laying the panels. The right subfloor can make a valuable contribution here.

The "enemies" of a beautiful terrace

In order to avoid unpleasant surprises such as sagging terrace slabs, the terrace must be protected from the causes. An uneven and unstable floor, for example, is not suitable for laying terrace slabs because it does not offer a stable footing. In addition, there is a terrace outdoors and is exposed to the weather conditions.

• the power of the sun heats the plates
• they expand with heat
• fine hairline cracks can result
• Rainwater penetrates
• Mosses grow in the cracks and enlarge them further
• in winter the penetrated moisture freezes
• Ice "blasts" the pavement apart

The sun will shine brightly every summer, there's nothing to be done about that. A terrace without sun is also hardly wanted. The expansion of the heated patio tiles must therefore be compensated for by the underlying material. At the same time, a flat base is created. Only those who use the right materials from the start can prevent moisture from causing irreparable damage later on.

The right substrate is essential

The right material underneath the terrace tiles is a crucial component when creating a terrace. It helps to level the surface and keep the deck permanently flat. This only works if the surface is suitable for it:

• he has to be flexible
• have sufficient carrying capacity
• Compensate for plate expansion with heat
• be frost resistant

As a rule, the selected area is only covered with pure earth at the beginning. Sometimes the new terrace should be built on an already existing concrete slab. But it is sufficient here if the surface is flat or flat. can be leveled?

earth as subsoil

A terrace is heavily used. The weight of furniture, planters and people acts on the patio slabs and the underlying soil. So that the terrace slabs do not sag afterwards, the earth must be compacted before laying. Loose soil is absolutely unsuitable as a substrate for terrace slabs.

• level the surface
• compact earth
• with vibrator

But even compacted earth alone is not enough as a subsoil. An additional supporting layer is still missing.

• grit or gravel and sand
• Slab bearing/pedestal bearing
• or mortar

concrete as a base

Terrace slabs are ideally laid on an elastic floor. But they can also be laid on a concrete floor. A few points must be observed.

• a layer of grit/gravel provides a flexible base
• alternatively lay with natural glue
• or in a bed of mortar or on drainage concrete

Use existing concrete slab

An existing concrete slab can be used to lay terrace slabs.

• the concrete slab must be intact
• hairline cracks and gaps must not be visible
• these would have to be closed beforehand
• otherwise there is a risk of moisture and frost damage
• there must be a gradient
• or subsequently made with screed

Lay patio tiles with adhesive

When the concrete floor is custom-cast, the terrace slabs can be laid with natural stone adhesive. Here, too, the subsoil must have a gradient.

• special natural stone adhesive is necessary
• the concrete slab must be absolutely level
• Rainwater must be able to drain off the house wall
• 2-3% slope required
• possibly. touch up with screed
• Seal the screed to the house wall
• Rain water can flow away from the house wall

Terrace slabs on a bed of mortar

Terrace slabs can be laid on a bed of mortar. It allows for the most precise alignment of the panels. However, this way of working is demanding and should only be chosen by experienced craftsmen.

• laying is done on fresh mortar
• Mortar should set quickly
• still allow for corrections
• Terrace tiles are tapped in with a rubber mallet
• you have to work quickly
• The laying surface must not be walked on before the mortar has set

grit as a substrate

Chippings, crushed stone and gravel are materials that are stable and flexible at the same time. They work well as a load-bearing layer on a concrete slab or directly onto compacted soil. It is the ideal laying method for hobby craftsmen. Sand is too fine and not suitable as a supporting layer alone.

• Suitable for gravel, chippings and gravel
• first load-bearing layer with coarse grain, approx. 20 cm
• then an approx. 5 cm high laying layer with a finer grain
• compact with a vibrator or roller
• Sand only suitable as the top layer
• Gravel is more stable than grit
• therefore suitable for heavily used terraces
• below the base layer is a drainage system
• Sealing of the house wall protects it from water
• Use of joint crosses ensures uniform joint widths

Before laying, the surface must be leveled with a board. The grit bed needs an edging so that the grit cannot slip away.

Drainage layer protects against water

The right material as a substrate is essential, but it still needs additional protection against water. A drainage layer, which fulfills important functions, is therefore required below the terrace slabs:

• Installed drainage mats form a layer that is permeable on one side
• seeping water is diverted away
• no water can penetrate upwards from the subsoil
• Frost damage is prevented
• unsightly discolouration caused by backwater is avoided

Alternative: Laying on adjustable pedestals

Pedestals offer a quick and easy way to lay terrace slabs.

• level and stable ground required
• possibly. even out and even out
• Stilt bearings are mounted
• should not be higher than 10 cm
• then they offer a secure footing
• Plan gradients
• Adjust the pedestal accordingly with the adjusting key
• Terrace slabs are then laid on pedestals

Pedestals are quick and easy to lay and offer even more advantages.

• inexpensive option
• Terrace tiles can be easily replaced
• for example if one of the plates is damaged
• Plates can be removed and the surface underneath can be cleaned
• Water can drain well
• Uneven floors can be easily compensated
• no frost problems, since panels do not rest on the ground

Learn more about building a terrace