Will Granite Countertops Stain?
I once had a Sales Rep swear to me that immediately following the installation of his brand new hardwood floors, he took a can of beans out of his pantry and, like Rob Gronkowski celebrating a touchdown, spiked it down onto his floor. His wife, horrified by the silver dollar-sized dent in their new walnut, demanded an explanation, to which the Sales Rep replied, “I’m just getting it out of the way. Now we can live our lives”.
The point my Rep was attempting to make (however over-the-top) is that obsessing over an interior surface only serves to detract from the experiences we create living on and with them.
Countertops are arguably the surfaces in our home that take the most abuse, and staining tends to be the most common form of damage.
This post provides a guide for understanding how stains occur on granite and other natural stone countertops. We can use this knowledge in the buying process to evaluate which countertops are best suited to the rigors of our unique lives.
Granite, as with all natural stones, can stain
The good news is that granite performs extremely well against staining. The bad news is that granite, like every natural stone countertop surface, will stain if certain precautions are ignored.
You may be thinking to yourself, “well, I’ve had granite countertops in the past that never stained”, and if so, good for you. It could mean that you knowingly or unknowingly took preventative steps to protect your granite.
It could also mean that you just didn’t see the stain. Granite, more so than marble and quartzite, tends to come in darker colors and more frenetic patterns, which makes it better at concealing stains. However, if you’re considering an aesthetic change to a lighter-colored granite countertop, you may not be so lucky.
In addition, it’s important to understand that “granite” is a very broad classification term, especially in the commercial sector, which, as you can probably guess, is less concerned with nuance than are geologists.
Not all granites are the same (and not all granites are granite)
The broader definition of granite is any stone containing a primary composition of feldspar, quartz, mica, and amphibole minerals. Geologists are far more concerned with the exact percentage composition and are not so quick to anoint stones with the “granite” label as granite distributors might be.
So why is this important? Well, to understand how a stone performs against staining, you’ll do well to understand that the countertop world deals in generalities, not specifics.
Think of the “Granite” classification as the “Canine” classification. All dogs are canines, but specific breeds have dramatically different behavior (foxes, wolves, and jackals are also canines, but you probably wouldn’t take one home to your kid, right?).
For this blog post, we’ll deal in generalities, but as with most topics in this complicated world, granite counters do not fall neatly into a single bucket.
All natural stones are porous
Stones are broadly categorized by the geological processes in which they were formed (you may even recall the terms sedimentary, igneous, and metamorphic from high school…). These processes describe the various ways that mineral aggregates fuse to form stone, and it’s this formation, along with the varying shapes and sizes of those aggregates, that mostly determines the likelihood of your countertop staining.
To illustrate, imagine pouring water into a jar full of oranges and a jar full of cherries. The oranges, due to their larger size and shape, do not fit as tightly in the jar as the cherries and therefore accept more water.
In this example, oranges and cherries are like mineral aggregates that fuse to form a stone. The open space within the jars would be similar to the pores created between mineral aggregates.
The greater the volume of the pores, the easier it is for the liquid to penetrate the stone. “Porosity” is the percentage of open space (the pores) to the overall volume of the stone (the jar of fruit).
Now, If we were to jam twice as many oranges into the jar, we would reduce the amount of available space for water to penetrate (also, if we were to use pinot noir instead of water, we’d have a nice sangria).
Like jamming oranges into a jar, in igneous and metamorphic formation, the stone is formed deep in the earth’s crust, where immense amounts of pressure and heat condense the mineral aggregates together.
Conversely, mineral aggregates that fuse on the earth's surface through sedimentary formation don’t face the same intense forces. Rather, they form through the erosion or deposit of sediments (like sand and mud) over time. Limestone is an example of sedimentary rock.
Now that we’ve discussed stone porosity and the role it plays in stain resistance, let’s discuss a similar concept that is more commonly used in the stone industry to measure stain resistance.
“Water absorption percentage” is the better metric for stain resistance
“Okay, got it, so in general, granite is less porous than limestone, but by how much? How do different types of granite compare in terms of stain resistance?”
If you talk to anyone in the countertop industry, they’ll tell you that it’s important to consider stone porosity in your countertop selection. Unfortunately, very few people will be able to provide you with a level of detail beyond that.
If you’re like me, you’ll want the actual data, but unfortunately, that data doesn’t always exist, and here’s why:
Porosity is measured in laboratories using Helium Pycnometers. Samples are cored from a stone and inserted into pressurized chambers of helium gas. The helium fills the stone's pores, and after the sample is removed, the volume of gas remaining in the chamber reveals the stone’s porous volume.
Can you imagine a bunch of portable laboratories equipped with Helium Pyncometers at every stone quarry in the world? Nah, never gonna happen.
…But maybe porosity isn’t the best way to measure stain resistance anyways?
Recall that porosity measures the total volume of porous space as a percent of the stone. To gauge a stone’s resistance to staining, what we want to know is how easily liquid travels through the stone.
We’d need to know the shape and size of the actual pores, e.g., are the pores narrow or wide? Continuous or obstructed?
The better (and more easily measured) metric for stain resistance is “water absorption percentage”. It’s similar to porosity, and both metrics are positively correlated. Still, water absorption % gets to the heart of what we’re after: The ease with which liquid will penetrate our granite countertop.
What’s more, measuring water absorption percentage doesn’t require fancy labs and equipment. Stone is oven dried and then submerged in water for 48 hours. The dry weight is then deducted from the wet weight to determine the absorbed volume. Easy peasy!
But here’s a reality check: If you go shopping for countertops and ask a countertop fabricator about the water absorption % of a particular stone, expect he/she to meet you with a blank stare.
If you’re going to find this data, you’ll need to do some internet sleuthing. Also, remember that stone is a product of geological formation, and Mother Earth is not a Tesla assembly line. Carrara marble from different quarries two miles apart will have different properties, but finding the water absorption % of typical Carrara marble will at least provide a general idea of its stainability compared to other stones.
Use any water absorption % figures as general guidelines in your selection process. The higher the %, the easier your countertop will stain.
Check out the chart below to see how some famous granites perform on water absorption tests:
Eliminate granite stains through prevention and maintenance
We know this is generic advice, but as of April 2022, the perfect, everlasting sealer has yet to be invented, so in its absence, prevention and maintenance are your only bets. The good news is that penetrating (or “impregnating” sealers) are super easy to apply, and maintenance consists of not letting juice and wine soak on your surfaces for long periods (we know, easier said than done— especially if you have little ones or lushes in your household).
But this is another topic altogether! We’ll be posting a blog about preventing and fixing countertop stains shortly. Join our mailing list for the latest countertop-related news and info.
Granite is a very broad classification, and some granites will perform better against staining than others. What you can count on is that granite will stain if not cared for properly.
If you’re going to consider countertops stain resistance in your selection process, it’s helpful to understand the role of stone porosity.
Though similar to porosity, the more common metric that you can look to is called “water absorption %”. Use this metric to help guide your decision-making process but understand that stone is formed through natural processes, so the counters installed in your home might not have identical characteristics as the information turned up through your research.