What a sealer does, and does not do
A penetrating, or impregnating, sealer soaks just below the surface and fills the stone’s pores, so water and oil sit on top long enough for you to wipe them up. It does not make stone stain-proof, and it does nothing to stop etching, the dull marks acids leave on marble and dolomite.
Which countertops need sealing
| Material | Seal? |
|---|---|
| Granite | Usually. Some dense stones barely absorb anything; some light, porous ones need several coats. |
| Quartzite | Usually. |
| Dolomite and marble | Yes. |
| Engineered quartz | No. Quartz makers say not to apply sealers. |
The hot-water test
The Natural Stone Institute describes a simple test. Pour a little hot water on the stone, leave it 10 to 20 minutes, then wipe it off. If the spot has darkened, the stone is absorbing water and needs sealing. If not, it is sealed. Try it in a few places, including near the sink, where the sealer wears fastest.
How often to seal
There is no single schedule, because stones and sealers differ. The Natural Stone Institute says a good sealer can last up to 10 years with the right daily cleaner, while some fabricators reseal every few years. The test above is the answer for your counter. Harsh cleaners wear sealers out sooner; see cleaning stone countertops.
How to seal
- Clean the counter with a stone cleaner and let it dry completely, ideally overnight.
- Read the sealer’s label. Directions differ; follow them over these.
- Test on a hidden spot first.
- Apply the sealer evenly, a section at a time, with a clean cloth or by spraying.
- Let it soak in for the time on the label, usually a few minutes.
- Wipe off all the excess before it dries. Sealer left on top dries to a hazy film.
- Add a second coat if the label calls for it, then let it cure before heavy use.
- Repeat the water test to confirm.
Common questions
How often should granite be sealed?
When the hot-water test says so. It can be years between coats on a dense stone with a good sealer, and sooner on a light, porous one.
Do quartz countertops need to be sealed?
No. Engineered quartz is not porous, and makers such as Cambria say not to apply sealers.
Does sealing stop etching?
No. Etching is acid attacking the stone itself. Wipe acidic spills quickly and use coasters.