How to identify the different types of natural stone to make an educated decision
Natural stone can be classified into two general categories according to its composition: siliceous stone or calcareous stone. Knowing the difference is critical not only to specify the most suitable stone for your projects, but also when choosing the cleaning products.
Siliceous stone is composed mainly of silica or quartz-like particles. It tends to be very durable and relatively easy to clean with mild acidic cleaning solutions. Types of siliceous stone include granite, slate, sandstone and quartzite.
Calcareous stone is composed mainly of calcium carbonate. Types of calcareous stone include marble, travertine, limestone and onyx. It is sensitive to acidic cleaning products and frequently requires a different cleaning procedure. What may work on siliceous stone may not be suitable on calcareous surfaces.
How to tell the difference?
A simple acid sensitivity test will determine whether a stone is calcareous or siliceous. All you need is about 100g. of a 10% solution of muriatic acid (alternatively you can use household vinegar) and an eyedropper.
Because this test may permanently etch the stone, use a sample or an off-cut or a corner several inches away from the mortar joint if already fixed. Apply a few drops of the acid solution to the stone surface on an area about the size of a 50p coin. If the stone is calcareous, the acid drops will begin to bubble or fizz vigorously. If little or no reaction occurs, the stone can be considered siliceous.
Rinse the area thoroughly with clean water and wipe dry. This test may not be effective if surface sealers or liquid polishes have been applied. If an old sealer is present, chip a small piece of stone away and apply the acid solution to the fractured surface.
Caution: Muriatic acid is corrosive and is considered to be a hazardous substance. Proper body protection is necessary when this acid is used. The test above is more for your general information than for you try. If not sure, simply contact us.
A polished finish on the stone has a glossy surface that reflects light and emphasises the colour and marking of the material. This type of finish is used on walls, furniture tops and other items, as well as flooring.
A honed finish is a matt/satin smooth surface with relatively little light reflection. Generally, a honed finish is preferred for floors, stair treads, thresholds and situations where the polished finish may wear off due to a heavier traffic of pedestrians. A honed finish may also be used on furniture tops and other surfaces, where a matt look-and-feel is desired.
A flamed finish is a rough textured surface used frequently on granite floor tiles or external paving. Its main benefit is the anti-slip properties.
Stone colours and appearance
Granite and marble are quarried throughout the world in a variety of colours with varying mineral compositions. In most cases, they can be identified by visible particles at the surface of the stone. Marble will normally show “veins” or high concentrations. The minerals in granite will typically appear as small flecks distributed uniformly in the stone. Each type of stone is unique and will vary in colour, texture and marking. That’s the beauty of natural materials after all!
Sandstone varies widely in colour due to different minerals and clays found in the stone. Sandstone can be light grey, cream/ yellow or pink/red. Dark reddish brown sandstone is also called brownstone, whilst Bluestone is a dense, hard, fine-grained sandstone of greenish-grey or bluish-grey colour and is quarried in the eastern United States. Yorkstone is a sandstone quarried in the York region of the U.K., in 2 main varieties: Buff Yorkstone and Grey Yorkstone.
Limestone is a widely used stone that is typically found in light grey, beige or buff colours. A distinguishing characteristic of many limestone materials is the presence of fossils that are frequently visible in the stone surface. Typically limestone is more porous and softer than marble, but there are exceptions. Portland Stone is a limestone quarried in the Island of Portland in Dorset.
Slate is usually dark green, black, grey, dark red or multi-coloured. It is most commonly used for flooring (especially outdoor) and for roof tiles. It is often distinguished by its distinct cleft texture.
If you are thinking of using natural stone in your project and have any question, speak to us. We are always happy to provide more in-depth information and assistance to make your next project successful.