Sealed vs. Unsealed Stone: What Every Marin Homeowner Should Know

Sealing is the most misunderstood part of stone care. It is sold as a magic shield, which it is not, and skipped as an upsell, which is worse.

Here is what a sealer actually does.

What sealing is

Most stone sealers are impregnators. They soak into the pores and leave a water- and oil-repellent barrier below the surface, so the stone looks unchanged. They do not sit on top like a coat of varnish, and they do not change the finish.

What that barrier buys you is time. A spill that would soak into unsealed stone in seconds instead sits on the surface for minutes, giving you the chance to wipe it up before it becomes a stain.

What sealing does not do

A sealer does not make stone stain-proof, and it does not prevent etching. Etching is an acid reacting with calcite-based stone — marble, limestone, travertine — and the acid reaches the stone through the sealer. Sealing a marble countertop is still worth doing; it just protects against a different failure mode than the one most people are worried about. The etching-versus-staining distinction is worth learning for exactly this reason.

It also will not fix a floor that is already soiled. Sealing dirty stone locks the soil in. Cleaning first is not an upsell, it is the only order the job can be done in.

The water-drop test

Put a few drops of water on the surface and wait five minutes.

• Water beads, stone unchanged when wiped: your sealer is working.
• Stone darkens where the water sat: it is absorbing. The sealer is worn or was never applied, and the surface is exposed.

Test the traffic lanes and in front of the sink, not a protected corner. Sealer wears unevenly, and the places that matter are the places that get used.

How long it should last in Marin

Two to three years is the normal range for a household floor, but exposure moves it a lot:

• Coastal properties. Salt air and marine damp shorten sealer life. In Sausalito we usually recommend the shorter end of the range.
• Shaded, damp locations. Canyon houses in Mill Valley grow organic film on slate and Saltillo faster than sunnier lots do.
• Entries and kitchens. These take the traffic and the spills. They will always need resealing before the guest bathroom does.

The other thing that kills sealers is household cleaning products. Strong high-pH cleaners, bleach, ammonia, vinegar, and general-purpose sprays strip them. If you have been cleaning your stone with whatever was under the sink, assume your sealer is gone regardless of when it was applied.

Why we seal after cleaning, every time

Cleaning opens the pores and removes what was in them. That is the only moment when the stone is clean, dry, and ready to accept a sealer properly. Which is why we recommend resealing every time we professionally clean a surface — not because it is an extra line on the invoice, but because doing it at any other time works less well.

If you want to know where your floors stand, run the water-drop test and text us the result. Or ask for a free estimate and we will assess sealer condition as part of the visit. More on the products and surfaces we handle is on our stone, tile and grout page.