FAQ
Thermal vs natural cleft bluestone: which should I use?
Natural cleft is bluestone split along its bedding plane: a textured, slightly uneven face with better grip when wet, less quarry work, and a material price of about $6–11 per square foot. Thermal (flamed) bluestone is heat-treated to a flat, uniform surface: cleaner to lay, easier to sweep, more formal, and about $9–14 per square foot in material because of the extra quarry labor. Both are the same stone, a feldspathic sandstone from the Catskills and northeastern Pennsylvania that absorbs under 2% water, so both survive Long Island winters. Use cleft where feet are wet, around pools and on shaded walks; use thermal for dining terraces and where an architect wants straight lines. Full-color and blue-blue grades are a color decision, not a durability one.
Last updated · Reviewed by Sag Harbor Masonry Co.
The same stone, two faces
Bluestone is a feldspathic sandstone from the Catskill Delta, quarried by around 150 mostly small operations across the New York–Pennsylvania border. Natural cleft is split along the stone's natural grain: the face keeps the ripples of the bedding plane, no two pieces are quite alike, and the texture is what gives it grip. Thermal (also called flamed) is sawn and then heat-treated so the surface pops to a uniform, slightly rough flat face; it takes more work at the quarry and costs more.
Cost
Material only: natural cleft about $6–11 per square foot, thermal about $9–14. Thickness adds $2–6 going from 1 inch to 1½ and 2 inches. Installed, a Long Island bluestone patio runs about $20–50 per square foot either way; the stone is the smaller part of the number and the base is the larger.
Where each belongs
- Natural cleft: pool surrounds, shaded walks that ice, steps, anywhere feet are wet. Also the right match for an old house where thermal would look too new.
- Thermal: dining terraces, formal courts, modern houses, anywhere an architect has drawn a straight joint line. Easier to sweep and to set furniture on.
Grades and thickness
"Full color" carries the browns, greens and rusts of the quarry; "blue-blue" is selected for the even blue-gray and costs more. Industry practice is 1-inch stone mortar-set on a concrete slab and 1½- to 2-inch stone dry-set on a compacted base; on Long Island, dry-set is the standard because the joints let the surface move with frost instead of cracking.
Durability and care
Both faces absorb under 2% water, the best varieties under 0.5%, which is why bluestone survives freeze-thaw here better than most natural stone. If sealed, use a penetrating silane or siloxane sealer that breathes, never a film-forming one, every 2–4 years (closer to 3 near the water or a pool). Cleft holds a little more dirt in its texture; thermal shows stains more evenly. Neither should ever be pressure-washed hard enough to lift the surface.
Services
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Pennsylvania and New York bluestone, laid dry on a compacted base the way Long Island frost demands, priced against 2026 Long Island ranges, plus pavers, brick and the outdoor kitchen that usually sits on it.
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