Sealing Granite Countertops:
The Real Test

The subject of sealing granite countertops and natural stone is full of conflict, confusion and controversy.

Not to worry! A couple simple tests will tell you what kind of stone you have, how to clean and care for it and if sealing granite countertops is necessary.

Determine Your Stone Type and
Sealing Requirements

Performing The Lemon Juice and Oil Test will tell you both how absorbent your stone is and what type of stone you have: Specifically, is it a silicate-based stone (granite) or a calcite-based stone (marble, travertine and limestone)... or possibly a mix of silicate/calcite.

Why is this important?

It will help you choose the best stone for it's intended use and/or help determine the characteristics of the stone you have say... if you just purchased a home and don't really know.

Granite is the stone of choice for use in the kitchen where all kinds of substances will come in contact with the countertop.

Some granites are more absorbent than others (not good) and some "granite" is actually mixed with calcite (like marble) and the surface will corrode or "etch" when exposed to acids like lemon juice, coffee, alcohol, salad dressing, etc. (not good).

Etching has nothing at all to do with sealing granite countertops or marble or travertine. Sealing will not prevent this.

It is a chemical reaction between the acid and the calcite that physically alters the stone, which is especially noticeable on polished surfaces.

All marble, travertine and limestone will etch and most are also prone to staining, which is why these stones are typically not recommended in the kitchen... unless you are willing to let them age naturally... spots and all.

But some of these stones are very dense and won't absorb a thing or stain at all, especially when polished, which helps decrease absorption rates for any stone.

You want a stone that won't do either (won't etch or stain) for the kitchen. That's granite.

So, this test is most useful to determine the best granite for your kitchen, wet bar or heavily used bathroom were lots of potions and lotions could be a problem.

NOTE: Perform this test on samples chipped off the exact slab you are considering for installation.

Also, this test could damage the surface polish of calcite-based stones, so if you are trying to determine the nature of a stone already installed, perform this test in an inconspicuous spot (in a corner or a spot that is always covered by an appliance, etc.)

Perform The Lemon Juice and Oil Test

1. Line up all your samples in row.
2. Drip enough lemon juice to form a dime-sized puddle on the first sample.
3. Do the same with vegetable/olive oil.
4. Look at the surface of the stone through the puddles and note the time.
5. If you see the surface under the puddles darken right away, this stone is very absorbent and should NOT be used in the kitchen.
6. If the stone does darken, but it takes 4 or 5 minutes, then applying a granite sealer will make this stone manageable in the kitchen... it'll be reasonably stain resistant.
7. If it takes 10 to 15 minutes to darken a sealer should still be applied, but make sure it absorbs well and doesn't dry on top.
8. If the stone never darkens or it takes 30 minutes or more, then you have a near stain-proof winner that probably would not take a sealer even if you tried.
9. Wipe the sample clean and look at the spot where the lemon juice was... is it dull compared to the shiny polish on the rest of the sample or did you notice the lemon juice fizzing/bubbling when on the surface? If so, it contains calcite and should not be used in the kitchen.
10. Perform the same test procedure on each of your samples.

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The Water Drop Test

If all you are trying to determine is whether sealing granite countertops or any other stone is necessary, you can perform the "Lemon Juice and Oil Test" using water. The reason for the lemon juice is to determine if your stone can handle contact with acidic substances. Of course, if it can't you don't want it in the kitchen... and the oil is very noticeable if absorbed.

So, drip a puddle of water on your countertop, note the time and observe.

If the puddle darkens quickly, then sealing granite countertops is required... multiple coats and annually for 3 years is not a bad idea and be quick about wiping up spills.

If it takes 4 or 5 minutes to darken... again a few coats of a good impregnator/sealer should be applied, but re-sealing every 3-5 years may be needed (possibly longer depending on quality of sealer... re-test when the time comes) and stains won't be a big issue unless something sits for a few hours.

If it darkens in 10 to 15 minutes, then apply a sealer, but follow directions carefully. Probably only one coat needed and should be many years before re-sealing is necessary

If the puddle doesn't darken or takes 30 minutes or longer, then you have a bullet proof stone that is next to impossible to stain. Sealing granite countertops in this category is really not necessary and should not be applied.

Client "peace of mind" is the primary reason many/most professionals recommend applying granite sealer when in doubt or even if it really isn't needed. This can cause unwanted problems and should not be done "just to be safe."

I recommend Stone Care Pro or SenGuard Sealers.

For complete step-by-step instructions on sealing granite & marble check out our All About Sealing Manual.

For most granites, applying a sealer even when not needed won't present a problem....

However, some dark granites (especially blacks and greens) are very dense and if a sealer is applied, it just sits on the top and can noticeably dull the appearance. If this happens, the sealer must be stripped and possibly the surface re-polished... an expensive pain.

If you have a dark, dense granite and need convincing, let a drop of oil sit on your sample overnight. Wipe it off. No spot? You will never stain this countertop.

If you notice a stain, wash it with a little soap and hot water and dry it. Stain gone? Your tops are essentially impervious to stains, but they will probably take one coat of sealer without issue.

Personally, I wouldn't bother in this case since the sealer is improving the stain resistance so minimally that it's not worth even the small chore and expense of sealing.

There ya go! Now you know the real test for sealing granite countertops and have the knowledge to make the best choice. Good luck and have fun!

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