How often should bluestone be cleaned?

Depending on use, usually periodic maintenance and annual deep cleaning.

Is impregnation mandatory?

Not always, but recommended outdoors and in heavy-use areas.

Why does bluestone become dull?

Due to improper cleaning, limescale deposits or wear.

Can you repair blue stone without replacing it?

Yes, through polishing, sanding or restoration mortars.

Cleaning, repairing, protecting and maintaining blue limestone

In summary

Blue limestone (Belgian bluestone) is a durable calcareous natural stone that is strong but sensitive to acids and aggressive cleaning. Always clean with suitable pH-neutral stone cleaners such as RC OS 2 or RC BIOZYM CLEAN and avoid vinegar, bleach and close-range high-pressure cleaning. Dull areas and scratches are restored through light sanding, polishing or satin finishing; larger damage with lime mortars such as St.One or a zinc oxide mortar such as RC AMONIT. Impregnation is preferably carried out with deep-penetrating silanes such as RC 900. Regular maintenance is essential for durability.

Blue limestone — also known as Belgian bluestone — is a durable calcareous natural stone widely used for terraces, floors, thresholds, façades, stairs and worktops. Despite its robust appearance, it remains sensitive to acids, unsuitable cleaning products and incorrect repair techniques.

What is blue limestone? Belgian vs Asian (and Irish) bluestone

Blue limestone is a compact blue-grey limestone often containing visible fossils. It combines high compressive strength with a relatively dense structure, yet remains vulnerable to chemical attack.

Differences between Belgian, Irish and Asian bluestone

Belgian bluestone

more compact and homogeneous
higher density
richer fossil structure
more stable finishing

Irish bluestone

generally less compact
lower density
more structural variations
in many cases, lower overall quality consistency

Asian bluestone

often more layered structure
sometimes slightly more porous
more sensitive to moisture penetration
variable surface quality

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Despite these differences, the basic principles for cleaning, repairing and protecting remain largely the same. Absorption rate and surface finish should be considered when selecting products and treatments.

Cleaning and maintaining blue limestone

Proper cleaning is crucial to prevent dull spots, discoloration and structural deterioration. Avoid acidic products (vinegar, descalers), aggressive chemicals, bleach and strongly alkaline cleaners. Also avoid abrasive materials and close-range pressure washing, as these can damage the limestone structure and create irreversible surface deterioration.

How to clean blue limestone correctly

Use lukewarm water with a small amount of pH-neutral detergent. Work with soft brushes or mops, limit water usage and allow the surface to dry thoroughly.

Professional pH-neutral cleaners:

RC OS 2 – Universal exterior cleaner suitable for periodic cleaning of mineral substrates and natural stone
Note: RC OS 2 may temporarily darken blue limestone. This effect is purely aesthetic and will disappear over time.
‍RC BIOZYM CLEAN – Enzymatic cleaner for organic contamination such as algae, grease and biological residues, ideal for terraces and exterior surfaces

Repairing blue limestone

Surface wear, improper cleaning or heavy use can cause dull areas, scratches or structural damage.

Removing dull areas, stains and scratches

Dull zones and discoloration are typically restored mechanically through polishing or satin finishing. The surface layer is carefully renewed using suitable pads, restoring color and uniformity while preserving the natural character.

Light to medium scratches are treated locally by light sanding followed by repolishing to achieve a uniform finish.

Repairing large pieces and structural damage

Broken corners, damaged edges or structural defects can be repaired using specialized restoration mortars such as:

St.One lime mortar by Saint-Astier: mineral lime mortar compatible with the structure of blue limestone, maintaining vapor permeability and ensuring visual and technical integration.

RC AMONIT zinc oxide mortar: high mechanical strength and excellent durability, suitable for high-load areas.

Impregnation of blue limestone

Due to its dense structure, impregnation is technically more challenging than with porous stones. When protection is required, use low-molecular-weight silane-based impregnations such as RC 900. This colorless hydrophobic treatment (10% active content) penetrates deeply, provides durable water repellency without forming a film, and preserves vapor permeability and the natural appearance.

Aftercare and maintenance

Regular maintenance is essential for long-term performance. Periodic cleaning with pH-neutral products prevents dirt accumulation, reduces staining risk and maintains aesthetic quality. Avoid aggressive products and perform maintenance in time to prevent deterioration.

Conclusion

Blue limestone is a durable, high-quality natural stone that retains its character for years when properly treated. Correct cleaning, professional restoration and targeted protection ensure long-lasting results. As every natural stone and every damage case is unique, repairs require a tailored technical approach. Our technical specialists are available to provide guidance, solutions and expertise for a professional and sustainable result.