Everything You Need to Know About Pennsylvania Bluestone

croppedimage450450 Cornerstone Travertine Flag 300x300 Everything You Need to Know About Pennsylvania Bluestone

The bluestone border creates a distinctive accent to the soft flowing travertine colors.

Colorful, beautiful and easy to maintain. There are a lot of good reasons to include Pennsylvania bluestone in your hardscaping projects.

In this blog post, we’ll take a closer look at the history, use and benefits of this outstanding stone.

Flagstone and bluestone

In order to discuss bluestone, we first need to talk about flagstone. Flagstone is a flat sedimentary stone with fissile bedding planes. It is naturally split into layers according to these planes and used for a variety of purposes, such as patios and pool decks, roofing, facades, and walkways.

Flagstone is bound together by minerals such as calcite, silica, and iron oxide. These internal materials are the cause of flagstone’s beautiful colors, one of which is a stunning blue leading to the name “bluestone”.

Flagstone History

The word flagstone stems from the Middle English word “flagge,” which means turf. In the thirteenth century, Europeans began using flagstone for floors, walls, and ceilings. It was especially popular for the interior rooms of castles.

Flagstone floors still exist in Scotland’s Muchalls Castle and Lindisfarne Castle in England. Chicago’s Portage Park is famous for its expansive flagstone decorations.

Pennsylvania’s Bluestone

Pennsylvania bluestone is unique to its part of the United States. Bluestone stems only from the state’s northeastern section as well as New York’s southern tier and northern New Jersey.

Bluestone is layered sandstone that comes in a range of colors, from a gorgeous blue to green, lilac, rust and more. It developed about 360 million years ago, when the seas pushed sand into the Catskills. In terms of composition, bluestone is made of mica, sand, feldspar, and various minerals. The distribution and composition of these minerals will determine how blue the stone is.

“True Blue” bluestone refers to stone that does not exhibit any other colors except blue when removed from a quarry.

Veins of true blue are rarer than full color – also called variegated – where  imbedded minerals create the waves of green, brown, and lilac colors mixed in with the blue. True blue flagstone consequently costs more than full color. However, true blue stone may still, over time, display other colors as minerals in the stone are exposed to the environment.

Preparing Bluestone for Use

In order to transform bluestone from the natural state found in the wilderness to stone that is ready to use in homes or businesses, it is cut out of the quarry into cubes.

Depending on the density of the stone, the cubes are then treated in one of two ways. The densest stone goes through a spalling process: Once removed from its natural environment, bluestone is cut along horizontal sections, thoroughly soaked with water and then heated with a propane torch. The spalling process produces thermal flagstone which features a perfectly even finish for the flagstone.

Less dense cubes (where layering is visible when removed from the quarry) will become natural clef flagstone after several weeks of air-drying.

During this time, the bluestone will naturally separate along fissures.  This separation results in an uneven but beautiful surface.  Both thermal and natural clef flagstone materials are excellent for any application.

Natural clef flagstone has always been less expensive that thermal because there is less processing involved. However, with that reduced price comes a surface variation that is not always acceptable.

Why Bluestone Is So Appealing

People love bluestone for its distinct color, incredible strength, superior density, and fine grain. It is most often used on decks and patios since it holds its color and is very difficult to break.

Bluestone is also used for walls, sidewalks, steps, indoor floors, and even fireplaces, as it can be cut into custom-sized slabs. The major drawback of bluestone is that is also holds heat making it potential quite hot after extended exposure to direct sunlight.

Bluestone Maintenance

Another part of bluestone’s appeal is that is easy to take care of. It doesn’t require sealing and is cleaned with only water and a brush.

If your bluestone is stained, just add some vinegar and water to the surface and scrub it out, although you can purchase specialty cleaners for unusual or severe stains.

The only other maintenance recommendation is a power washing once every few years. Bluestone owners should take care not to power wash on the highest level as the stone can be grooved by intense water pressure. Bluestone is one of the easiest surfaces for homeowners to maintain.

Would you like to learn more about Pennsylvania Bluestone? Contact Woodward Landscape Supply. Better still, visit us in person to see this marvelous, durable stone for yourself.

20 thoughts on “Everything You Need to Know About Pennsylvania Bluestone

  1. Holly Scheideler

    Hello! I installed a bluestone patio in September and now that the snow has melted I notice some of the pavers have crumbled or flaky areas on their surface. Is there anything I can do prevent this from happening. Do you know why this is occurring? Thank you. Holly

  2. Dale Downing

    we are considering buying a kitchen island with blue stone on the top. The salesman said that it stains and is hard to care for. What do you think?

  3. Joe

    I know a lot of people use bluestone for their hearth, but Could you give me any advice on whether I can use bluestone to actually line the firebox (floor and walls, rather than firebrick) of my outdoor fireplace?

  4. Todd Braun

    I have a bluestone patio. Would like to re-grout the joints. Would I risk damaging the stone if I used a grinder to remove the old grout? Should I just touch up the joints. What kind of grout would I use?

  5. Reade Elliott

    Is there an acceptable range of stone thickness for 1″ Natural Cleft Bluestone and 1 1/2″ NC Bluestone? In short, can you expect 1/2″ stones in the lot of 1″, or 1 1/16″ thick in the lot of 1 1/2″?

    1. woodward Post author

      Natural clef flagstone can be quite a range around the nominal size. 1″ can be 1/2″ to 1 1/2″. 1 1/2″ can be 1″ to 3+”.

  6. Patrick Donnell

    I’m considering using the blue flagstone for a patio but was told that it has the possibility of rusting,in that correct?

    1. woodward Post author

      The color of flagstone is caused by the minerals in the ground which forms it. You can see greens, browns, lilac along with the classic blue in what is called full color flagstone. If there is iron in the stone it will create a rusty brown color. If the iron is inside the stone you buy and not yet exposed to the air, the rust may be released some time after the installation as the stone weathers. This is normal aging. It is also possible you will never see rust if the stone you acquire doesn’t have iron content. There is fundamentally no way to know this. Rust is unusual in thermal and in true blue flagstone because of how it is sorted before being packaged for sale — but not impossible.

  7. K Jill Browning

    We have a bluestone sidewalk and front porch. I am assuming due to all the rain/wet weather we have had here in VA for the last year, we have noticed several of our stones seem to be very slick when wet. My son fell last week , and I am on a mission to keep that from happening again. Should we just gently power wash?? I see no color of anything “growing”. Thank you for your response.

    1. woodward Post author

      If your flagstone seems slick when it is not raining, there has to be a coating on it of some kind. Perhaps a moss developed from our damp weather or even something from treating the grass or gardens that got sprayed on it. I would power wash and even use an outdoor cleaner such as CLR.

  8. Cynthia G.

    CAN I use a sealant on my bluestone sidewalk/porch? You said it is not necessary, but due to the constant rain we have been having, and the snow in winter, my bluestone has been peeling in layers in some places, and cracking. What sealant can I use on it???

    1. woodward Post author

      There are natural stone sealers available, concrete sealers will not help and could make a real mess. Most hardscaping dealers offer something for stone. Our selection is from SRW – SRW Natural Stone sealer. Check out their website for more information.

  9. Mike Kelly

    Hired a power washing company to clean my house. Should I worry about any solution they use affecting our Bluestone walk?

    1. woodward Post author

      It is always possible that a specific chemical will leave a stain or residue on stone, concrete, siding, etc. it is not likely but if concerned, see if they can give you a sample of the solution and test in on a small area

  10. Elizabeth Butters

    My family has had a circa 1784 house for with a bluestone patio for 35 years. I’m trying to figure out how old the patio is. I’m guessing it was installed sometime between the 20s and the 50s but I’d love to know more about when bluestone may have bugun to pop up as a patio material in rural New Hampshire.
    However old our patio is, it’s held up great btw- we encourage moss to fill in the gaps in between stones to keep out weeds as there is no filler between stones. We have never had an issue with the patio and have never had any maintenance work done.

    1. woodward Post author

      Sounds beautiful. I don’t know the exact time when flagstone emerged as a patio material but I do know it is over 200 years ago. The fieldstone walls you see in Gettysburg, for example, are made from the stone that is the top layer in a flagstone deposit. I have seen historical houses in the 200 year old range using this stone. I actually think it is older.

  11. Lori K

    Several stones on my bluestone patio have turned black. I tried scrubbing with a brush and soapy water, but the black didn’t come off. Is this lichens, algae, or something else? What can I use to remove the black?

    1. woodward Post author

      All outdoor materials (e.g., flagstone, concrete, siding, shingles) are subject to some change in appearance driven by environmental factors. However, I have never heard of flagstone turning black; so, I have no idea what is causing it. You could try cleaning with a stronger cleaner to see if it makes a difference. There are professional stone cleaners and even acids (which can be effective but require great care in their use). But, I can not promise any of them will remove the black since I don’t recognize the issue.

  12. Mike

    I just had 20 yards of 3/4 bluestone put down and the color is a light gray the bluestone I have up front is a deep blueish will the new stone turn darker once the rain has hit it a few times?

    1. woodward Post author

      2B clean, aka 3/4 bluestone, does not come from the same quarries as Pennsylvania bluestone but it is formed in the same environment so the same minerals are at work creating color. It will definitely darken as it ages just as your PA bluestone did. Although they will not be identical, they will be compatible.


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