Namur bluestone is a hard, blue-grey to blue-black limestone quarried in the Belgian Meuse valley around Namur and Huy. It consists almost entirely of calcium carbonate and belongs to the family marketed as Belgian bluestone or petit granit.
Properties
- Colour — blue-grey to blue-black, occasionally with a brownish cast; weathered surfaces take on a silver-grey tone
- Texture — fine-grained and dense, often with visible fossil fragments (crinoid stems, shell) showing as pale flecks
- Water absorption — low, which makes the stone frost resistant in a temperate maritime climate
- Compressive strength — high for a limestone, so it performs under load as a cill, tread or kerb
Applications
- Cills and thresholds — the classic use, beneath windows and doors
- Stair treads and steps — strong and hard-wearing, though more slippery when wet
- Facade cladding and plinths — as bands, surrounds and base courses in masonry facades
- Interiors — floors, window boards, fire surrounds and worktops
- Restoration — replacing historic elements in listed facades
Finishes
The appearance depends heavily on the finish. Honing gives an even matt face; polishing darkens the colour and adds gloss; tooled and fine-picked finishes give a linear texture; bush-hammering or flaming produces a rough, slip-resistant surface — the right choice for treads and external paving.
Points to watch
- Limestone is acid sensitive. Never use hydrochloric acid or an aggressive facade cleaner; both etch the surface and leave permanent marks
- Clean with water and a neutral detergent, and mask bluestone while cleaning surrounding brickwork
- Corroding ironwork (cramps, railings) causes brown staining and can split the stone; use stainless fixings
- Weathering shows as layered flaking and a pattern of small cracks meeting at right angles — a familiar sight on old bluestone elements
- Provide adequate falls and a drip groove under cills so water does not track back onto the wall
Related terms
- Bluestone
- Natural stone
- Cill
- Limestone
- Facade cladding
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