1) Vegetation becomes established in the small cracks that form between the slabs if they have not been laid correctly.

It can also develop on the surface in some cases. The advantage of Bluestone is that any deposits can be simply washed off by pressure-washing with water, since the stone is not porous and does not therefore allow vegetation to grow from within it.

2) If water gets under the stone through the joints or by seepage, it could dislodge the slabs in the event of a hard frost.

1. LAYING.

1. Terraces at ground level

It is important that the structure should not be able to move; the procedure to achieve this is generally as follows:

- remove soil to 40 to 50 cm below the anticipated level of the terrace
- apply a root-proof sheet
- lay 20 to 30 cm of well-tamped gravel or inert rubble
- add 15 to 20 cm of stabilised sand with a slope of 1.5 to 2% towards the outside
- lay the bedding mortar to a thickness of 5 to 7 cm
- lay the Bluestone

Recommended stone thickness: 5 cm

2. Terraces on a concrete substrate

Since concrete does not drain off water with the attendant risk that it will penetrate below the level of the Bluestone paving, it is imperative that the substrate should slope 1 to 2% towards the outside and that a drainage mat (sold in rolls) be provided under the bedding mortar.

In this way, the water will be able to seep out without any risk of freezing and dislodging the slabs.

Recommended thickness: 3 cm

3. Joints

Please refer to interior flagstones and add a water-repellent additive to the mortar.
If expansion joints are provided in the screed, they will also be required in the paving at the same location.

2. MAINTENANCE.

Al that is required in order to remove grease stains after a barbecue, for instance, is to wait for it to rain (remembering that Bluestone is not porous). Should it prove necessary, add 2 tablespoonfuls of ammonia to a bucket of water and pour it over the paving: this will restore its original appearance.

Annual maintenance using a pressure-washer with water will not be a problem; however, do be careful with the joints.

Note: A terrace, a base, a monument, etc. in Bluestone which has been poorly maintained over a very long period of time can be made to look new again using a liquid solution of potash-alum (wet the stone, allow it to act overnight and wash off).

Exterior
flagstones. Exterior flagstones.
Interior
flagstones. Interior flagstones.

1. LAYING.

1. Traditional laying using mortar on a bed of stabilised sand.

This consists of laying the slabs using cement mortar or cement and lime mortar on a bed of stabilised sand spread over a rigid substrate. The thickness of the layer of mortar is to be between 1.5 and 3 cm and that of the stabilised sand between 2 and 5 cm.

This technique can be used in most cases; however it is inadvisable for under-floor heating. For this special case, N.I.T. 174 by the CSTC should be referred to.

The following materials are to be used:

1) Stabilised sand, which is to be a mixture of:

- sand free from impurities and 0 to 5 mm grain size

- white cement in a ratio of 100 to 150 kg of cement per m³ of sand

2) Bedding mortar consisting of a mixture of:

- class 0-2 mm white sand, free from impurities

- white cement in a ratio of 1 part cement to 4 parts sand

the amount of water added is to be kept to a minimum in order to reduce risk of staining the stone.  

2. Laying using cement adhesive on a screed which has set.

This type of implementation is only suitable for gauged thickness slabs and if the screed is perfectly flat.

The manufacturer’s instructions are to be referred to in order to ensure that the cement adhesive does not risk staining the stone.

3. Joints

1. for movement

- It is a mandatory requirement that expansion joints be carried over to finishing structures and hence to the flooring, regardless of the method of laying

- Sectional joints are used to separate the substrate from adjacent structures and to subdivide large areas into smaller sized sections.

NB: The need for these joints to be allowed for will be governed by the intended laying method.

2. finishing

Apart from their aesthetic function, these joints should be capable of accommodating variations in the sizes of the flagstones due to their dimensional tolerances.

Width in mm
< 1.5 ( ✻ )
Between 1.5 and 2
> 2
Mix
Pure cement slurry
3 parts cement to 1 part fine sand
1 part cement to part fine sand
; dimensional tolerances permitting

Preliminary notes

1. These recommendations have been drawn from Memorandum of Technical Information No. 213 published by the Centre Scientifique et Technique de la Construction [CSTC = Construction Scientific and Technical Centre].

2. You will not be fully satisfied with your floor unless it has been laid by skilled installers using the appropriate techniques.

3. It must be borne in mind at all times before, during and after laying the flooring that excess water is highly detrimental to the stone.

4. Laying technique

There are certain special and specific precautions that are required for laying a natural material.

1) As a general rule, any superfluous addition of water is to be avoided; this involves:

- waiting sufficient time for the substrate to dry

- when laying with mortar, use a mortar with minimum water content

2) Stone is a natural material that can exhibit slight variations in appearance, even within the same batch. In order to achieve an even and harmonious result, the installer should ensure the slabs are well mixed before laying them.

3) Once the slabs have been laid, the mortar/stone combination must be allowed to dry off naturally. Care is therefore to be taken to provide suitable ventilation, avoiding draughts, direct sunlight or fierce heating. In addition, sheets or boards are not to be laid over the job on completion in order to protect it, since they would slow down the drying process considerably.

2. MAINTENANCE.

Preliminary note:

However, and as with all materials, its properties are such that it requires a minimum of maintenance in order to encourage its patina to form.

It is with this in mind that the various recommendations for items laid in interiors or exteriors are summarised in this chapter.

1. Maintaining interior flagstones

Before doing anything, it is essential that freshly laid flagstones are left to dry.

A period of 3 to 6 months is essential for theme to evaporate the water from the substrate, the water from the fixing agent as well as the moisture contained in the slabs themselves, which are rarely dry on being laid.

The greater the amount of water added in the construction of the flooring system, the longer the drying period required.

Throughout this drying period, the only form of cleaning recommended is with a floor cloth dampened with clean water in order to prevent the material from becoming “sealed” which would inhibit or block water evaporation.

After this period it is recommended that a neutral household type of soap in flakes dissolved in hot water be used. This soap should nevertheless be used in reasonable proportions (a handful in 10 litres of water), any excess is liable to form an unsightly film on the surface of the flooring.

Acid cleaners obviously must not be used .

Products specifically intended for natural stone can also be found in the shops (e.g. Lithofin brand). These products work well for the most part, provided the manufacturer’s instructions are observed meticulously and excessive amounts are not used.

Regarding the removal of a milky white deposit resulting from laying and grouting and which could not be eliminated completely after laying, by cleaning with whitewood shavings for instance, the following procedure is recommended:

- Allow the milky deposit to dry

- Vacuum the floor

- Scour it using a mildly alkaline cleaner (maximum pH 10) and on no account any acid product.

This operation is made easier with a single brush floor polisher fitted with a felt disc impregnated with the cleaner.

It is preferable in all cases to work on small areas at a time rather than spreading the cleaner over the entire area to be cleaned.

- Wipe off using a floor cloth moistened with clean water.

Final note:

It is quite common for small black marks to appear on the surface of the flooring and for it to flake off after a while. This is a characteristic of the structure of all limestone and will have no adverse effect on its lasting durability.

2. Maintaining kitchen worktops

We will remember the large solid Bluestone water troughs under the hand pumps used by our forefathers.

Unpleasant surprises may cause concern in the early stages.

Acid liquids can lighten the colour of the decorative surface of the stone; how can we explain the fact that old worktops have been kept so beautiful? It is quite simply because the years have given them that patina which is so typical. In order to compensate for the absence of this patina and to protect your worktop, you can apply a solution consisting of one part turpentine and one part linseed oil to the surface. Allow to dry for 48 hours and remove any surplus. In the event of any accident occurring subsequently, repeat the application using a 2/3 to 1/3 mixture. For day-to-day maintenance, clean the worktop using the same liquid as you use for washing up or by simply wiping over with a cloth dipped in a little salad oil.

You can also treat the stone using a water-repellent and oil-repellent product from the Lithofin range or Dry Stone by Nord Resine.