Natural Cleft vs. Thermal Bluestone
Which Type Is The Right Choice For My Project?
Customers often ask us about the different types of bluestone they can use for walkway and patio projects. Fortunately, the decision is simple—there are only two options: Natural Cleft Bluestone and Thermal Bluestone.
To help you choose the right material, let’s break down the key differences between natural cleft and thermal bluestone. Both begin as large blocks extracted from the quarry. However, natural cleft stone typically comes from layers closer to the surface, while thermal-grade blocks are taken from deeper sections. Although both are genuine Pennsylvania Bluestone, each is finished using a different manufacturing process.
Natural Cleft Bluestone
Natural Cleft Bluestone offers the classic, traditional look many homeowners love. Its split-face texture features natural high and low points—known as the “cleft”—on the top and bottom surfaces. This naturally textured finish provides excellent slip resistance, making it a durable and reliable choice for both outdoor and indoor applications.
Natural cleft bluestone splits along the natural fissures inside each quarried block. This split creates the high and low points—known as the “cleft”—on the surface of the stone. Because the stone breaks naturally, its thickness will vary. For example, a nominal 1″ piece typically ranges from 3/4″ to 1 1/4″. Likewise, a nominal 1 1/2″ piece usually ranges from 1 1/4″ to 2″.
Natural Cleft Bluestone is available in two color ranges – Full Color or Blue/ Gray.
Photos of the natural cleft stone can be seen here- https://robinsonflagstone.com/pa-flagstones/full-color-range-natural-cleft-pa-flagstone
https://robinsonflagstone.com/pa-flagstones/bluegray-range-natural-cleft-pa-flagstone
Thermal Bluestone
Thermal Bluestone features a smooth, thermal‑flamed surface that creates a clean, modern look. Because it is sawn and thermally finished, this material offers greater consistency in thickness, size, and squareness compared to natural cleft stone. Thermal Bluestone may look smoother, but it still provides reliable slip resistance. This makes it a dependable choice for walkways, patios, and a wide range of landscape projects.
The thermal bluestone is saw-cut to an exact thickness (1”, 1 ½”, etc.). The surface is then flamed with a blowtorch to create a little bit of texture on the face of the pieces. Due to it’s consistent thickness and squareness, the thermal material tends to be a little easier to install than the natural cleft.
Thermal bluestone is available in two color ranges – Variegated or Blue/ Gray.
Additional photos of the thermal stone can be seen here- https://robinsonflagstone.com/pa-flagstones/thermal-paving
In conclusion, choosing the right bluestone for your project is a simple process. First, decide whether you prefer natural cleft or thermal bluestone. Next, select the color range that best fits your design. After that, consider how each finish complements the overall look you want. Finally, remember that both options work beautifully for any paving application, so you can’t make a wrong choice. Ultimately, it all comes down to personal preference.