Stone Types

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Marble & Limestone

Granite

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Natural stone is rapidly making its way into the showrooms of most new development sales offices. With this popularity, we’ve seen an increase of calls from homeowners who were not properly informed on the differences between stone types, or what to expect with regards to durability and long term maintenance.

This post aims to sort the many types of natural stone we encounter into more generalized groups based on their maintenance attributes. For each family we will give a brief description of the following : stone use, hardness of the material (scratch resistance), their susceptibility to etching (acid resistance), porosity (sealing schedule), and ease of repair.

Harness scale

Below is a rough outline of the hardness scale of the natural stone families we service. The mohs scale is not strictly logorithmic, nor is it a linear scale. At he lower (softer) end of the scale, differences between hardness are less extreme, wheras at the middle and higher end of the scale (harder) the differences are very extreme. This implies the difference between say, talc and limestone is relatively subtle, but the difference between marble and quartzite is far greater (quartzite being harder than marble by orders of magnitude). This scale does not account for mineral weaknesses, such as acid solubility in calcite based materials like marble and limestone.

Marble, Limestone & Travertine

Brief:

Why group these materials together? The rate of servicing, susceptibility to etching and ease of repair is all very similar between these materials due to their mineral composition and hardness. Keep in mind they are not alike with regards to density and appearance, mainly due to how they are formed (metamorphic vs. sedimentary). Marble and limestone are quickly becoming very common materials for kitchen countertops, but have long been used in baths or as a floor surface. Many people find marble and limestone much warmer aesthetically when compared to granite. Marble is much more elegant than travertine due to its unique patterning and lower rate of imperfections, being a metamorphic stone, marble is much denser/finer grained than most limestone and travertine, making it an excellent candidate for natural high gloss finishes. Prices vary when it comes to buying marble and limestone, but generally speaking travertine is the most budget friendly of this group. As a side note, since travertine is so often filled with imperfections, it wears very well over time, making etching and traffic patterns very difficult to notice, I would consider this the most maintenance free material if you appreciate it’s natural variations.

Susceptibility to Etching: 10

These materials are all similar in their mineral composition, and very reactive to acids, they will etch easily.

Hardness: 3-4 (Mohs scale):

Since marble is mainly composed of calcite, it is rated at a hardness of around 3-5 mohs. For this reason we usually recommend having a good carpet to collect outside dirt and grit, and regularly dust-mopping to remove any grit brought in from the outdoors. Outdoor sediment is rated at around 6-7 mohs, which will easily scratch and wear away at these calcite based materials.

Porosity:

Like granite, it is hard to determine how porous your particular material may be, however unlike granite, all marble/limestone/travertine surfaces are porous. As a general rule, marble and travertine are less porous than limestone. Often these materials require on site sealing post installation, even if they are advertised as already sealed. High traffic areas with regular exposure to moisture and steam (showers, baths, pools etc.) will require sealing more frequently.

Repairability: 10/10

These calcite based materials are a pleasure to work with due to their softness and predictable grain patterning. We can with relative ease isolate a damaged area for repair and match it’s surrounding finish. Unlike granite, it is much easier to transform these materials from a polished finish to a honed finish, or anywhere in-between.

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Granite

Brief:

Granite is ubiquitous with luxury counter tops, until the last decade or so, it was very rare to see marble or specialty materials (ceasar stone, onyx, epoxy etc) installed in a kitchen. Due to it’s incredible hardness as well as affordable cost (roughly 25% cheaper than marble) it’s no surprise that granite continues to dominate as a reliable countertop material. From an aesthetic perspective, it is not uncommon for granite to be referred to as a “cold” material, I suspect this is why it is rarely used as a floor tile in residences. While most granite is very consistent, showing little variation in colour or patterning, veined varieties do exist. A veined granite will generally appear closer to a marble or quartzite, appearing “warmer” while remaining durable, impervious to etching, and not particularly porous. While veined granite is beautiful, it is much rarer and thus significantly more expensive than regular granite, of course, it will need much less maintenance than marble, so long term savings should be considered.

Hardness: 6-7 (Mohs scale):

Granite is roughly twice as scratch resistant when compared to marble. It is unmatched as an exterior building material due to it being very dense, and nearly impermeable.

Susceptiblity to Etching:

Simply put, granite DOES NOT ETCH. The mineral composition of granite is mainly silica, quartzite and feldspar, none of which react to acids.

Porosity:

Generally speaking, granite is one of the least porous materials we encounter, but this is not always true. In our experience, lighter granites are more porous than darker (denser) granites, and it is not uncommon for clients with absolute black granite counters never using sealer, while lighter granites may quickly show signs of absorption if left unsealed. To check for yourself, let a moist sponge or paper towel (clean water) sit on your stone for a few minutes, then look for signs of absorption (darkness).

Repairability: 6/10

Being so durable and resistant to staining, granite rarely needs servicing beyond silicone replacement and sealing. At the same time, it’s hardness means any grinding or resurfacing will be significantly more labour intensive when compared to marble. For example, an equally worn marble floor would take anywhere from ¼ to ½ the amount of effort to re-surface when compared to granite. Simply put, granite repairs are not often needed, but when they are, they are expensive.

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Quartzite

Brief:

Natural quartzite (not to be mistaken with quartz aggregate material such as Caesar Stone, Vicostone etc.) has become more and more popular over the last few years. We do not consider it a ‘mainstream’ product due to cost, and it is rarely encountered outside of custom applications. Aesthetically, some consider natural quartzite the epitome of beauty in a slab of stone. Quartzite slabs often exhibit a subtle transparency, filled with beautiful crystalline veins, and often with very consistent colouring. The main downfall of natural quartzite is that it is often mislabled. Dolomitic marble being sold as quartzite can leave you with an acid reactive, softer material than expected. True quartzite is harder than granite, unable to be scratched by glass or your average knife, and absolutely impervious to the common sources of etching like vinegar and most cleaning products. A common example of mislabled quartzite is "superwhite", which is actually dense dolomitic marble, NOT quartzite. "Taj Mahal" is an example of extremely resiliant true quartzite, requiring no sealing, is impervious to etches and will not display scratches with regular use. There are many resources and testimonials available online, we recommend thorough research and to test your slab to be certain it is etch resistant if that is your aim. Take time to express these concerns to your supplier before purchasing slabs. You can also do your own testing with your local supplier to be sure:

1: To test for hardness, you can use a chunk of "quartzite" to scratch a piece of glass, it should leave scratches behind, whereas marble will not.

2: To test for etch vulnerability, vinegar can be left to sit on the surface of the slab, if it's true quartzite, it will not etch.

Susceptibility to Etching: 0 (if it is actually quartzite)

Hardness: 7 (Mohs scale):

Quartzite is consistently gauged to be as hard or slightly harder and more resistant to scratching than granite. Like onyx, if a slab is prone to etching, etched areas will likely be less scratch resistant due to weathering.

Porosity:

Like granite, quartzite porosity will vary slab to slab. Generally speaking, quartzite is much less porous than marble/limestone, but still requires sealing. Quartzite is much less prone to the discolouration seen in poorly maintained marble, but deposits of minerals within the quartzite can still cause discolouration if not properly maintained.

Repairability: 5/10

Quartzite is often on par with granite when it comes to repairs, however it has some unpredictable qualities. Quartzite often has deposits of other minerals which do not polish to the same lustre as the rest of the slab, the physical pressure applied during original manufacturing cannot be replicated on site, making matching the original luster difficult in some slabs. To date we’ve managed to always match the finish, but are aware of this limitation and feel it is worth mentioning. Due to the transparent nature of quartzite, clear epoxies with longer curing times may be necessary, adding time/cost to chip and crack repairs.

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Visit our Blog post "The Quartzite Quandary" where we outline a few of our experiences with quartzite, as well as instructions on testing a slab to determine if it is actual quartzite or a softer, mislabelled material.

Quartzite Quandary

Onyx

Brief:
Onyx is a dramatic, translucent material that has always been used for it’s unique patterning (banding) and dynamic colouration. We usually see this material used as furniture tops and powder room/bath counter tops. Onyx is on par with marble with regards to maintenance needs, which is why we rarely see it used in kitchens or as a floor tile in high traffic areas. Onyx looks best polished to a high gloss finish, as this reveals is transparency, unfortunately this means there is no low maintenance solution if you choose to use it in a vulnerable area of your home. Due to the transparency of onyx, it is a prime candidate for backlit applications, including countertop islands, reception tops, or as a unique wall covering. Back lighting will accentuate the fine concentric layers of mineral deposits (banding) within the stone and reveal its depth. Expect this material to cost more than your average slab of crema marfil (marble).

Susceptibility to Etching: 10

Onyx is very reactive to acids, it will etch easily.

Hardness: 5 (Mohs scale):

Onyx is typically denser and harder than most limestone and marble. While slightly harder, it is still very susceptible to etching and softening due to introduction of acids. Onyx is slightly harder to scratch than most marble, but still too soft to be considered resilient. It's worth noting here that we have chosen to label this at a level 5 hardness even though onyx is typically labelled at a 7. The difference between these two harness levels on the mohs scale is extreme. Our experience grinding countless onyx countertops and a few floors does not leave us with the impression Onyx is anywhere near as hard as natural quartzite (actually a 7).

Porosity:

Onyx is considered a porous material, and should be treated the same as marble with regards to your sealing schedule.

Repairability: 8/10

The tools and compounds used to polish marble are also used with onyx, and the material itself responds very well. Due to its hardness, some extra smoothing techniques are required to bring it to a full gloss polish. Because the material is translucent, clear epoxies with longer curing times may be needed to repair chips or cracks, this can also add to cost.

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Slate

Brief:

Slate is the only material mentioned that is not a candidate for resurfacing. The surface of a slate tile is it’s natural finish, which consists of a subtle rough but generally consistent texturing. Because it is relatively soft compared to even marble, slate is often coated with topical finishes to protect it from turning chalky and scratched. Over time this floor finish may fail or collect dirt at which point it can be stripped and sealed with a colour enhancer or even a clear penetrating sealer, in most cases we recommend non-topical coatings. The recommended method of sealing depends on the location of the material, traffic, and desired appearance.

Susceptibility to Etching: 0

Slate does not etch, but topical coatings generally found on slate may react to solvents or other chemicals, lightening the area and looking similar to an etch.

Hardness: 3-4 (Mohs scale):

Slate is quite soft, and will display scratching and wear relatively quickly when exposed to the elements. This isn’t necessarily bad, as it does wear consistently if a rustic appearance is desired.

Porosity:

Slate is not particularly porous, but this varies from where it is sourced. Since slate does absorb sealer readily (both clear and colour enhanced penetrating sealers) it is safe to assume oil and other contaminants will quickly penetrate into most raw slate surfaces. If a topical coating is applied sealing is not needed as often, but once dirt has penetrated into the topical finish or discolouration occurs, stripping the floor finish is required before new sealer can be applied.

Repairability: 2/10

Since slate tile is generally left in it’s raw form, resurfacing is not possible. Scratched or high points cannot be removed without making the affected area look drastically different from the original finish. Most of our slate repairs consist of stripping topical coatings and either applying a penetrating sealer (both clear or colour enhanced) or re-applying a thin layer of topical coating if the customer prefers a glossier finish. Chips and cracks can be repaired with a colour matched epoxy, but again will not match the natural finish.

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