Sealing Granite and Other Natural Stone
Sealing granite, marble, travertine and other natural stone is essentially stain-proofing your stone. If you have an unsealed light colored stone and you spill red wine on it the wine may get into the micro-pores of the stone and leave a stain which can remain there even after many cleanings. This is because you cannot get to the bottom of those pores to clean out the product which caused the stain. The best way to avoid this is to use an impregnating sealer which will fill those micro-pores with a clear solid. A basic law of physics is that two products cannot occupy the same space at the same time so by using a sealer you are not allowing the pores to remain open and for the stone to get stained.
An impregnating sealer does not affect the gloss of the stone when used correctly as it does not stay on the surface level. It sinks into the stone. If you use too much and it stays on the surface level it will generally cause a problem like a milky finish, a smeary surface or a greasy residue on top of your stone, none of which would appeal to me and I doubt they would appeal to you either.
When to Seal Your Stone
Pour a 3” circle of water on the stone and let it sit there for a minute or two, then wipe it off with a dry cloth. If after you have wiped the stone the area where the water stood is darker than the rest of the stone then it is absorbing water and is in need of sealing. While some will say that you should reseal your stone every 6-12 months that is not usually necessary. You can test your stone every 6-12 months with the “water spot test” as in above and as long as the stone is not getting darker it is not in need of sealing.
Realistically once you stone is sealed if you clean it with a Ph balanced cleaner you should not have to reseal it for years unless you treat the stone with an alkaline. The way to remove a sealer and a stain is to treat it with an alkaline solution as this will re-emulsify the stain or sealer and allow it to be removed from the stone. S when you are using Drano, Easy-off, lye soap or any alkaline products try to avoid contact between them and your stone.
What Stone Sealer to Use
When your stone does need to be sealed you need to look at what you want the sealer to do for you besides stain-proofing the stone. Do you want the stone to appear exactly like it looks dry? If so you want to use a regular impregnating sealer like Hydrex, Proseal, or Protex.
On the other hand, if you want the stone to appear darker (like it looks when it is damp) then you want to use a color enhancing impregnating sealer like Ager or Ager Tiger. These will both work for color enhancing a stone, also known as the “wet look”. The difference is that the Ager Tiger is meant for stones with larger pores (exotics and stones with lots of movement to them). If you use regular Ager on stone with large pores what can happen is that in time the Ager continues to move into the stone and may drop below the visible level and take the “wet look” with it resulting in you losing the color enhancement that you liked.
The Stone Sealing Process
Regardless of which sealer you choose you need to apply it correctly. Start with a clean dry stone. If you washed it you should let it dry out for at least a day, but the longer the better! I usually have found that two coats of sealer is enough for me but sometimes 3 was necessary. When in doubt here is a good rule of thumb – as long as the stone is still absorbing the sealer you can keep applying it. When it is no longer absorbing the sealer wipe the excess off with a clean, dry rag and allow it to set up for 24 hours so it cures. While the sealers are all liquid, the part that actually stays in the stone is a solid. The liquid is merely the agent to deliver those solids into the stone and it will evaporate or dry out within 24 hours.
While there are some stones which are so dense they do not absorb anything (Black Absolute comes to mind) I think that the peace of mind you get sealing your stone will far outweigh the cost involved if there is any chance of your granite or stone becoming stained. The products we have discussed here will protect against both water and oil based liquids. When in doubt I seal it.