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Flagstones and a Thermal Finish

5/31/2012

3 Comments

 
If you’ve been reading my posts regularly and perusing my website, then you probably have figured out that I am big fan of flagstone.  It’s versatile, natural, durable, comes in a wide range of colors, shapes and sizes, and can be used as a key ingredient in nearly any design concept, from rustic to traditional to sleek and modern.
 
I’d like to focus this week’s post on an available finish referred to as thermal finish.  For the sake of conversation, I’ll be referring mostly to the most commonly used flagstone in our area, PA graystone.  But the terms I’ll be using can be applied to many other stone types as well.

Most of the flagstone commonly sold for residential applications is what is called “natural cleft.” The stones themselves are flat and comfortable to walk on, wheel the grill across, or set up your patio furniture upon.  However a close examination will reveal a slight texture to the surface of the stones. The texture reveals slight sedimentary patterns from the creation of the stone and generally fluxuates no more than 1/8” from high spot to low spot.

In my experience, most clients and homeowners like the look of the natural stone grain, however in some instances the finish may not be for everyone.  Another option is the thermal finish.
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PA Graystone -- Natural Cleft
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Also PA Graystone -- Smooth Thermal Finish
“Thermal” refers to the heat treatment that helps to provide a smooth consistent finish to the surface of the stone.  I’ll spare you the nitty gritty of the science details, but the basic process includes moistening the stone and then applying a flame directly to the stone surface. As the moisture hides in the small nooks and crannies of the stone surface, it eventually expands due to the heat, resulting in a small “popping”and flaking of the stone surface.  As the treatment continues, the subtle texture of the stone grain is removed, leaving behind a smooth consistent surface.  In some instances, the thermal treatment also achieves a slight change in color, however that often depends on the make-up of the stone, specifically the iron content of the stone.

Generally speaking, most natural cleft flagstone is split along the natural sedimentary grain as it is harvested from the quarries to achieve the desired thickness.  Thermal finish stone is typically saw cut to the desired thickness to achieve a more consistent stone thickness.  After the stones are cut to the desired thickness, the surface is thermal-treated to remove any minor imperfections and saw marks. The result is a flagstone that is uniform in thickness and completely smooth across the surface of the stone.

The thermaling, or torching as its sometimes called, is not a process that should be attempted by do-it-yourselfers.  While it is something that can be done by qualified contractors on site for smaller edge treatments or spot flaming, the process can be somewhat time-prohibitive for larger scale surface areas.  Most suppliers can provide thermal-treated stones available directly from the quarry, at just a slight cost increase from the natural cleft stone.

Ultimately the choice to go with natural cleft vs. a thermal finish is up to the homeowner and their particular aesthetic preferences.  A few locations that lend themselves more to a thermal finish may include pool side installations where users are more apt to be barefoot, interior floors, and countertop applications, however the natural cleft may better suit a project, again based on the personal preferences of the homeowner and the desired architectural effect.  Many more formal installations also utilize the thermal finish for larger steps, pedestals, blocks and caps.

If you would like to see a sample of thermal finish vs. the natural cleft, please feel free to ask and I’d be happy to show you a few samples.  You can also visit your local hardscaping supplier to see what they may have available in stock.


 
3 Comments
Matt link
6/4/2012 01:05:05 pm

Nice explanation Clark.

Reply
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10/12/2019 02:17:07 am

I do not really have a lot of knowledge concerning stones, so I could use this blog. Well, it is not like I need to learn about them, but I just want to. I really do hope that I get a chance to use this knowledge that I acquired. Not only is it a nice thing to know, but I really do feel like I can use them someday. I want to be able to put this information that I know to great use.

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4/22/2022 10:33:05 pm

I am a mechanical engineer and thermal science is much important part of it .It includes solid works, surface finishing , welding, di manufacturing. I have a lot of information of modern solid works.

Reply



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    Clark Kent Creations, LLC is a full-service landscape construction company servicing the Pennsylvania communities of Delaware County, Chester County, The Main Line, and the University City, Art Museum, and Manayunk/Roxborough neighborhoods of Philadelphia.  In addition to this blog page, additional information regarding the company and our services can be found on the subsequent pages of the site.
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    Clark Linderman is the president of Clark Kent Creations, LLC, a landscape construction company based in Swarthmore, PA.  He is a proud graduate of the University of Michigan.  In addition to his passion for all things outdoors, he counts Michigan football, Phillies baseball, Superman memorabilia, Memphis R&B music, and good craft brews among his many interests.  He currently resides in Swarthmore with his wife, Sheila, two sons, his dog Krypto, and a really, really messy garage full of work supplies and toys.

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    Clark Kent Creations, LLC
    Swarthmore, PA
    Design and Construction to Maximize Your Outdoor Experience

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    If you like the content of my blog posts, here are a few other blogs that I check in on regularly:

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