How
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Yep... your countertops can still be stained even when sealed.
Granite countertop sealers simply help decrease the absorbency rate of the stone, so it won't stain as easily. Sealers don't absolutely prevent a stone from being stained, they just make it a lot harder to do.
I recommend Stone Care Pro or SenGuard Sealers.
How Sealers Work
Sealers, also called "impregnators" are composed of a resin dissolved in water or a petroleum-based solvent. The granite sealer is applied to the stone with a paint brush or pad and left on the surface long enough for it to be absorbed into the pores of the stone (i.e. below the surface). Excess sealer is wiped off the surface and the rest evaporates leaving the resin to clog up the pores... hence the term impregnator.
Once cured a sealer keeps spilled substances on the surface of the stone giving you more time to clean it up, so that it is not absorbed into the stone causing a stain. But if coffee, wine, oil or other substances are left on the stone long enough, stains may occur even when the stone is "sealed."
Why?
All stones are porous. Some readily absorb virtually anything spilled on them while others are so dense that essentially nothing is absorbed or it takes a very long time.
Logic tells us that the more porous the stone, the faster and deeper it will absorb any spilled substance. An impregnating granite countertop sealer will clog up the pores preventing a deep stain, but sealers work below the surface, thus staining can still occur at the surface level.
Highly porous/absorbent stones (like most marble) need to be sealed and periodically re-sealed to adequately control absorbency and the tendency to stain. Thus, such stones are not the best choice for used and abused areas like the kitchen.
And some granites (and other stone types) are so dense that they really don't need a sealer.
In fact, applying a sealer to dense stones (most notably black granites like Black Galaxy or Absolute Black) may only result in a build-up of sealer residue and a dull surface without any appreciable benefit or stain protection since the stone is already extremely resistant to staining.
Also, it's important to remember that not all stones in the same commercial family (granite, marble, travertine) perform exactly alike. In fact, performance can vary considerably.
Therefore, it's important to test the stone to determine if it is suitable for it's intended use (kitchen countertop, bar top) and whether or not it should be sealed.
Etching
Plenty of confusion surrounds the mysterious "water spots" and "glass rings," which people often mistake for stains. These are not stains. Nothing has absorbed into the stone and sealers cannot prevent this and have NOTHING at all to do with it.
This problem occurs with calcite-bases stones like marble, travertine, limestone and potentially even with some granite that has calcite in it. Calcite crystals react with acids like fruit juice, alcohol, vinegar, coffee, etc. spilled on the surface.
The reaction, called "etching," corrodes the surface, destroying the polish and leaving a dull spot on your countertops or floors. And it can happen in just seconds. The spots are not as noticeable on a honed surface, but it still occurs. Another reason why calcite-based stones are not the best for kitchens.
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So... before installing a particular stone, test a sample to be sure it will stand up to your intended use.
Sealing Frequency
Of course, sealer quality can vary, but most granite countertop sealers should last 3-5 years and some are rated for 10 years if the stone is diligently and properly cared for. And cutting-edge sealers like SenGuard create permanent bonds with the stone requiring only a single application.
Practically speaking though, sealers break down over time, are degraded by cleaning products and general use. And even when sealed, the absorbency rate and tendency to stain remains more a function or characteristic of the particular stone than the sealer.
Porous stones will still be more susceptible to surface stains and should be sealed more often (every 1-3 years depending on use), while dense stones really shouldn't be sealed in many cases or may need only one application and never again.
Using the simple "Water Drop Test" will tell you when it's time to re-seal your countertops or floors.
You Can Do It!
Well, there is certainly a bit of hysteria regarding granite countertop sealers and the real need for sealing is generally overblown. Much of it is recommended and done simply for "peace of mind"... and that's ok for the majority of natural stone installations. Most stones should be sealed and re-sealed at some point.
It's definitely easier and far less expensive to re-seal your stone more than is really necessary than to hassle with removing stains or paying for marble restoration.
On the other hand, be prudent and careful in your application when choosing to seal dense stones that may not really need it. You might end up having to pay to strip the sealer when it just sits on the surface dulling your countertops.
But now you know how granite countertop sealers work and what to expect from them, I'm sure you feel more comfortable and won't have any problems. Good luck with your project!
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