Is Sealing Granite Countertops Necessary?

After you’ve upgraded your home with a new set of granite slab countertops, it is time to face the inevitable question: To seal or not to seal? If you know anything about granite, you have almost certainly heard of sealer products, which soak into the stone and protect it from harm.

Sealing is indeed a great idea, but it’s not always necessary. Is sealing granite countertops necessary? In this article, I will give you all the information you need in order to find out for sure.

Is Sealing Granite Countertops Necessary?

There isn’t a simple and easy answer to this question. One would think that there would be an easy answer, since all granite is the same, right? Wrong. There are many different types of granite, and this is why sealing granite countertops is sometimes necessary and sometimes not.

The Many Types Of Stone

All rocks fit into one of three categories: Sedimentary, igneous, and metamorphic. There is no need to explain every detail, so here is the short version: sedimentary rocks are made of compressed sand or dirt like sandstone. An igneous rock, like granite, was formed by lava that flowed out of the earth many centuries ago. Metamorphic rocks are sedimentary/igneous rocks that have undergone a change due to the pressure and heat that exists deep within the earth.

So Which One Is Granite?

Granite is classified as igneous rock, but did you know that some types of granite are partly sedimentary? You see, geologists separate granite into two categories: I-type granite and S-type granite. As you can tell by the letters, I-granite is completely igneous, while S-granite is partly sedimentary. That explains many of the differences between high-grade granite countertops and low-grade ones.

There are also A-type granites, though they are less common. These granites contain a lot of basalts, another igneous material which may be porous or non-porous. When basalt is formed from lava, it sometimes retains air bubbles, causing it to take on a porous texture. Thus, if you buy an A-type granite, you will probably need to use a sealer.

So why does this make such a big difference? Because a sedimentary rock is porous, while an igneous rock is not. A stone that is porous can absorb liquid and hold it in the hollows of its many pores. When you’re using granite for a kitchen surface, which must deal with a variety of liquids, that’s a big problem.

The Importance Of Composition

You have probably noticed that granite comes in many different colors and combinations of colors. Those colors indicate another difference between the various types of granite. Granite has that banded, variegated appearance because it is composed of multiple minerals. These minerals give each type of stone its distinct color. Here is a quick guide that will allow you to judge the mineral content of granite by its coloration.

  • Semi-Transparent White = Quartz
  • Chalky White = Calcite
  • Opaque White = Feldspar
  • Salmon Pink = Potassium Feldspar
  • Black = Biotite
  • Dark Brown = Biotite
  • Gold or Yellow = Muscovite
  • Dark Green = Amphibole
  • Dark Red = Hematite and/or Iron Oxide
  • Blue = Labradorite
  • Green = Amazonite

You should also bear in mind that some “granite” slabs are not actually granite at all. There are quite a few granite lookalikes in nature, although they do tend to be very similar to the real thing. For instance, blue Anorthosite is sometimes sold as “blue granite” even though it is actually just a reasonable substitute.

What Can Happen If You Are Wrong?

Let’s look at this question from both angles. If your stone does not need sealing, and you attempt to seal it anyway, there will be one problem. A non-porous granite will not absorb the sealer, which means that you will only get a surface layer. Because the sealer isn’t meant to be used on non-porous stone, it will be more difficult to apply. So, you will end up wasting time and money, and the sealer probably won’t work properly.

On the other hand, let’s say that your stone does require sealing, and you neglect to do so. Any liquid that is spilled on the surface will be able to soak into the stone and do damage. Water will be the least of your worries, as most countertops have to deal with much worse. A kitchen counter needs to handle mild acids like orange juice or vinegar, as many mild acids are encountered in the kitchen. Acid will etch porous stone very quickly, and can even ruin it entirely. It also needs to withstand common cleaning chemicals that it may also encounter.

For a granite sink top located in a bathroom, the risk is even greater. The chances of this slab being exposed to chemicals are much higher, and there is a much greater variety of chemicals at play. When these chemicals seep down into the porous stone, they can stain it terribly and might eventually cause cracking.

How To Test Your Granite

There are two simple tests that you can do in order to see if your granite countertop needs sealing. These are the water test and the acid test.

The Water Test

This one couldn’t be any simpler. You just drop some water onto the countertop and see what happens. Let the water sit in the same spot for about 15 minutes, and then wipe it off. If the stone has absorbed the water, there will be a dark spot in the place where the water sat. This indicates that the stone has absorbed the water and definitely needs to be sealed. If you don’t see that dark spot, your stone is completely non-porous and does not require sealing.

The Acid Test

Don’t worry; we won’t be using any dangerous acids here. Some lemon juice will do the job nicely. This test is very similar to the water test, actually. Just drip some of the lemon juice onto a part of the counter that is out of sight. If the stone is porous, you will see the lemon juice absorb into the stone. However, you will also see an etching effect as the acid eats away at the stone and causes a chemical reaction. This chemical reaction produces a stain that will not go away without sanding. Stones that contain calcite are particularly vulnerable to etching.


I could literally write entire books about the differences between the various types of granite. Of course, some people have already done that, so you can certainly check that out if you want to know more. Considering the high cost of granite, it certainly never hurts to do your research.

Thankfully, you don’t need to be a geologist to choose a suitable piece of granite for your home. You just have to know what to look for, and maybe perform a few simple tests. Some people will advise you to avoid porous stone just because it requires sealing, but I find that those sealer products aren’t usually too expensive. Most of them do the job quite well, so there’s no need to worry as long as you follow my advice.

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