The success of a natural stone patio depends as much on the choice of stone as on its installation method.

Several solutions are possible depending on the existing substrate, the nature of the ground, the thickness of the slabs, and the project budget.

It is important to distinguish four main methods:

• bound installation, where the stone is laid directly into fresh mortar;
• bonded installation, where the stone is bonded to an already prepared and hardened substrate;
• installation on a compacted foundation with draining mortar, which allows for a patio to be built without a concrete slab;
• loose-lay installation on aggregate, which is simpler and more economical.

These different constructions do not have the same cost or the same implementation constraints.

1. Bound Installation – NF DTU 52.1

Bound installation is the traditional method for laying natural stone paving.

The stone is not bonded to an already dry screed: it is laid and leveled directly into a bed of fresh mortar.

This technique is particularly suitable for natural stones with variations in thickness, as well as for certain traditional pavings, particularly opuses.

When carried out on an admissible substrate and in accordance with applicable requirements, this technique falls under NF DTU 52.1 relating to bound floor coverings.

The Laying Mortar

The mortar directly forms the bed in which the stone is laid.

Outdoors, we prefer to use a draining mortar based on cement and aggregates, rather than a very dense traditional mortar.

The objective is to facilitate the drainage of water that may penetrate through the joints or the natural stone.

Ensuring Stone Adhesion

The laying mortar alone does not offer the same adhesion as an adhesive mortar.

It is therefore recommended to ensure the bond between the stone and the fresh mortar using a slurry or a bonding mortar suitable for natural stone.

The stone is then directly placed in the fresh mortar and leveled to the desired height.

Joints and Drainage

Outdoors, it is essential to provide suitable joints and a sufficient slope to allow for water drainage.

On very impermeable substrates, a drainage or decoupling system may also be provided depending on the site configuration.

2. Bonded Installation – NF DTU 52.2

Bonded installation is different from bound installation.

The substrate here is already prepared, hardened, stable, clean, and sufficiently flat. The stone is then fixed directly onto it using a suitable adhesive mortar.

The principle is therefore:

cementitious substrate → adhesive mortar → natural stone

There is no several-centimeter-thick mortar bed created simultaneously with the installation.

This technique falls under NF DTU 52.2 relating to the bonded installation of ceramic and natural stone coverings, when the conditions specified therein are met.

When to Choose Bonded Installation?

This method is particularly suitable when a concrete slab or an appropriate screed already exists.

The substrate must specifically be:

• stable;
• sufficiently flat;
• clean;
• properly constructed;
• equipped with a slope suitable for water drainage outdoors.

Any cracks, movements, or slope defects in the substrate can affect the paving. The quality of the substrate is therefore essential.

The adhesive mortar must also be chosen according to the stone, its format, its thickness, and the substrate.

At Minéral, we offer adhesive mortars suitable for natural stone, such as ARDEX X77, depending on the application.

3. Installation on Compacted Crushed Stone and Draining Mortar

It is also possible to build a natural stone patio without first pouring a concrete slab.

The construction then relies on a properly prepared and compacted crushed stone foundation.

The principle is:

prepared ground → compacted crushed stone → draining mortar → bonding mortar → natural stone

The crushed stone forms the foundation of the patio. Its installation and compaction are crucial for the stability of the structure.

A layer of draining mortar is then laid on top. The stones are placed on this mortar with a suitable bonding agent.

This solution offers several advantages:

• it avoids the need for a concrete slab;
• it provides a stable substrate;
• it promotes water drainage;
• it limits movements compared to a loose-lay installation on gravel.

This method is often referred to as installation on a draining screed. However, it is more accurate to speak of installation on a draining mortar bed on a compacted foundation.

This construction should not be automatically equated with a bound installation compliant with NF DTU 52.1: the substrate and the composition of the structure must be studied according to the site and the specifications of the products used.

4. Loose-lay Installation on Compacted Crushed Stone and Aggregate

Loose-lay installation on aggregate is the simplest solution when one wishes to avoid creating a concrete slab or a mortar bed.

The principle is:

prepared ground → compacted crushed stone → gravel bed → natural stone

At Minéral, we prefer a draining aggregate rather than a simple sand bed.

This construction allows water to drain easily and has the advantage of being relatively simple to install and repair.

However, since the stone is neither bonded nor bound, the patio is naturally more susceptible to movements and settlement of the substrate.

The quality of the foundation and the peripheral blocking of the paving are therefore particularly important.

What Stone Thickness?

This technique generally requires slabs that are thick and strong enough for loose-lay installation.

The choice of thickness must be made according to the stone, the format, and the use of the patio.

What Joints to Use?

A traditional rigid cement joint is generally poorly suited to a structure that may move slightly.

Instead, we prefer:

• filling with sand or suitable aggregate;
• or a polymer joint compatible with draining installation, when the product and joint width allow.

Polymer joints offer the advantage of remaining relatively flexible while limiting sand leaching and weed growth.

Which Installation Method to Choose?

There is no single method suitable for all projects.

You Already Have a Concrete Slab or a Suitable Screed

Bonded installation is generally the simplest solution when the substrate is compliant, sufficiently flat, and properly constructed.

You Want a Traditional Installation

Bound installation allows the stone to be laid directly into a bed of fresh mortar. It is particularly suitable for stones with differences in thickness or certain traditional pavings.

You Do Not Want to Create a Concrete Slab

Installation on compacted crushed stone and draining mortar is a particularly interesting solution, combining stability and drainage.

You Are Looking for the Simplest and Most Economical Solution

Loose-lay installation on crushed stone and aggregate limits masonry work, with the trade-off of less stability than a rigid construction.

Drainage: An Essential Point Outdoors

Regardless of the chosen method, an outdoor patio must be designed to prevent water stagnation under the paving.

An appropriate slope, water drainage, the nature of the substrate, drainage, and edge treatment must be anticipated from the design stage of the patio.

The natural stone, joints, and various materials forming the patio must function as a whole.

Key Takeaways

Bound installation: the stone is laid directly into fresh mortar.
→ NF DTU 52.1 when the substrate and implementation fall within its scope.

Bonded installation: the stone is bonded to an already hardened substrate.
→ NF DTU 52.2 when its requirements are met.

Installation on draining mortar and crushed stone: the stone is laid on a bed of draining mortar built on a compacted foundation.
→ a solution that avoids the need for a concrete slab.

Installation on aggregate: the stone is laid loosely on a draining bed.
→ a simple and economical solution, but more sensitive to substrate movements.

In case of doubt, the choice of installation method must be adapted to the selected stone, the terrain, the existing substrate, and the constraints of the construction site.

The Minéral teams can advise you on the choice of natural stone and suitable installation products for your project.