Sealing granite countertops and the question of whether it is a necessity is something that crosses the minds of many homeowners that currently have granite installed and also a consideration for those in the process of determining if natural stone countertops are the right choice for their home.
Granite, Onyx and Marble are natural creations and one stone slab is not like any other in the world. The unique beauty of each stone is why many homeowners decide on natural stone.
These unique characteristics also mean that no two stone slabs have the same absorbency qualities. A slab from the same stone family or even the same quarry may appear similar, but have a different threshold for absorbing liquids. In today's stone industry, many factories are cutting the blocks of granite into slabs, polishing them and using a resin treatment to fill micro-fissures, pitting and other minor characteristics considered by some consumers as imperfections. When a stone is polished the pores are tighter. Polishing, in combination with the resin coating restricts the ability of liquids to enter.
What does that tell us? Stones that are inherently resistant to liquids, and those polished and treated at the factory, may not accept a sealer or repellant. An after-market sealer applied to this type of stone can leave a hazy film on the surface. The good news is that the stone may not require a sealer. If a sealer won't penetrate into the stone, neither will a stain.
With factory honed surfaces, or softer and more porous stones, liquids can enter the surface more freely and therefore require a sealer. It doesn't matter where the stone is located in your design, fireplace surround, island top or bathroom vanity; if it’s a softer stone, then there’s a chance it might need sealing to protect it from everyday elements. This is especially true in outdoor applications. A sealant will provide UV protection to your stone from burning or discoloration of the resin coating.
Applying an impregnating sealer is a common precautionary practice against staining. Only a low percentage of natural stone surfaces need to be sealed because granite is the main stone variety in use, and not all granites are fully absorbent. It’s important to note, sealants are more accurately described as a repellent than a sealer and do not make the stone stain proof, but it does help make the surface more stain resistant. Some high traffic areas or places frequently exposed to moisture and sun may need to be sealed more often than others. When the surface doesn’t repel water or oil, the surface needs to be protected and it’s time to apply or reapply with the brand of sealer originally used.
The following absorbency test works for granite and almost all other stones to determine if your stone needs a sealant. Leave water on the slab for 10 minutes and then wipe dry; if the stone doesn’t appear darker in that area, then granite won't absorb water-based material that may stain it and it won’t absorb a water-based sealer, either.
You can use a similar test to determine if your stone can be stained by oil based products. Dab mineral oil on the slab and leave it for 5 minutes. If that area appears darker after you remove it, you should use a solvent-based sealer to protect against oil based stains. The area darkened by the mineral oil for testing purposes will eventually completely evaporate, leaving the stone its natural color. If it doesn't darken the stone, oil or other common household petroleum based agents shouldn’t stain it either.
In short, if there isn't a change in color after testing with these two liquids, you don't need a sealer on your granite countertop.
Marble is the one natural stone that is the exception to the rule when it comes to sealants. Due to the inherent qualities natural to marble, an impregnating sealer will not protect marble against water rings, oil spots and stains. In fact, blemishes on the surface may appear as stains or unfinished areas, but in reality the surface is etched, caused by corrosion between the calcium in the stone and common acidic fluids that come in contact with the stone. Once Marble has been etched, no amount of sealer will bring the color back, it needs to be resurfaced.
When considering sealing, remember that sealing the stone does not make the stone stain proof, it makes it more resistant to staining. If a sealer is applied in a food preparation area, be sure that it is non-toxic and safe for use.