Flagstone is a sedimentary rock that has been used for paving since the early 1900s.

Understanding Basics of Natural Stone

Sedimentary stone is created by the hardening of sediment layers by pressure and low heat, usually under water. It often consists of layers or strata of sand, clay or organic sediments. The hardness and strength of sedimentary stone varies considerably.

Igneous rock is formed from hot, molten material which cools and becomes solid. It may have been molten lava at shallow depths or magma.

  • Examples: Granite, basalt

Metamorphic rocks are formed when heat, pressure, fluids and strain act to change sedimentary or igneous rocks into materials with different characteristics This is what transforms sandstone into quartzite and limestone into marble under heat and pressure.

  • Examples: Quartzite, marble

What this means for you...

Sedimentary sandstone from Arizona has been used in flagstone patios since the early 1900s, so there's been a long time to test its suitability. Light weight, pale color and resistance to heat absorption has made it a popular choice in the Southwest where pool decking can become impossibly hot in the summer. However, the porosity of this material makes it problematic too, and in many conditions homeowners are redoing their patios with harder flagstone alternatives such as metamorphic quartzite for these reasons:

  • Moisture absorbed into sandstone can expand to cause flaking.
  • Significant problems occur adjacent to irrigated areas due to overspray.
  • Hard freezing may cause displacement of individual flags.
  • Chlorinated swimming pool water can create significant damage.
  • Wear and tear causes gradual erosion of the surface that leads to low spots.
  • Areas where water collects can leave significant stains on the stone itself.
  • Years of spills and grilling spatter can irreparably discolor sandstone.
  • Pro Tip: We prefer to use harder materials such as quartzite because so many softer flagstones have degraded very quickly, particularly around swimming pools and other areas subjected to significant stress. In our experience, sandstone flakes, cracks and most of all it is subjected to stain and discoloration. We've had to tear out many of these problem patios and rebuild them from the ground up. Our customers are willing to pay for dense flagstone because it's an investment that holds its value over time. - Micah Helkenberg, DC West Construction in Carlsbad, CA

List of important things to remember when you select flagstone:

  • Choose flagstone that's available in as many shapes, sizes and thicknesses as possible.
  • Beware that glittery flagstone can lose this sparkle under wear and tear.
  • Brightly colored stone may prove softer than more uniform muted tones.
  • Has this stone been tested in residential landscapes over time?
  • Does the stone originate near my project site for minimal shipping charges.
  • Is the stone widely available through different sources so I can compare costs?
  • Where water is mineral rich, beware of dark colored stones that show efflorescence.

Flagstone Terms Defined

Bluestone: A durable sedimentary flagstone quarried in Pennsylvania and Connecticut

Ledgestone: Relatively flat strips of stone for stacking.

Milled: Flagstone cut to an edge on one or more sides.

Mosaic: Patterns made up of random pieces.

Pavers: Cut flagstone into square or rectangular units.

Steppers: Flat stones used as pathway step stones.

Sawn Bed Veneer: Stone cut to a certain depth with natural surface on one side.

Slabs: Large flat pieces of stone with irregular outlines.

Snapped Veneer: Stone snapped to provide flat surfaces on both sides.

Thin Veneer: Flagstone cut to lay on concrete slab.

Treads: Stone machined to suit step treads or risers.

Tumbled: Processed to soften edges.

  • Pro Tip: We make flagstone recommendations according to the style of our clients’ homes and the type of landscape they are looking for. The most popular stone choice in our area is Colorado Buff. It is a material that is gathered from northern Colorado. We like the multi-colored look that ranges in color from chalk to rust to brown tones. The difference in color and texture is what gives this stone a wonderful character. In addition, it is a very dense stone with great ASTM ratings that allow it to weather the tough Colorado winters. - Roger Haywood, Accent Landscapes in Colorado Springs, CO
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