· Michael Blair
Concrete sealer gets sold on a schedule and applied on faith. It does real work, particularly in a climate that cycles through freezing repeatedly each winter, but the right interval depends on the sealer type and the exposure rather than on a calendar someone printed on a bucket.
What a sealer is actually protecting against
Water getting into the concrete and then freezing. Middle Tennessee does not have deep sustained cold, but it has a great many freeze-thaw cycles, which is arguably worse. Each cycle expands water inside the pore structure and works the surface apart, which shows up as scaling and a sandy texture.
Second is staining. Concrete is porous and oil, rust, leaf tannin and de-icing residue all soak in rather than sitting on top. A sealed slab gives you time to clean a spill before it becomes permanent, which is most of the day-to-day value.
The two families of sealer
Penetrating sealers, usually silane or siloxane based, soak in and react below the surface. They leave the concrete looking unchanged, they do not make it slippery, they do not peel, and they are the right default for a driveway. Reapplication is typically measured in several years rather than annually.
Film-forming sealers, generally acrylic, sit on top and leave a sheen that darkens the concrete. They look good on decorative and stamped work and they are what most stamped concrete needs. They also wear, cloud and eventually peel, and they need recoating far more often.
- Penetrating silane or siloxane: invisible, long interval, best for driveways
- Acrylic film: wet look and colour, shorter interval, right for stamped work
- Epoxy and urethane: garage and interior slabs, not exterior driveways
- Never film-seal a slab that has a moisture problem underneath
The interval, honestly
A penetrating sealer on a residential driveway in this climate generally holds for several years. The test is simple: sprinkle water on the surface. If it beads, the sealer is working. If it soaks straight in and darkens the concrete, it is time.
Film sealers on decorative work need attention more often, and the interval is set by how worn and cloudy the film has become rather than by the date. Resealing a film sealer that has not worn just builds thickness, and excess build is what causes the milky white blush people blame on the weather.
Timing and the mistakes that ruin a job
New concrete must cure before it is sealed, generally around a month, and sealing it early traps moisture that has to leave. Seal on a dry slab with several dry days ahead and moderate temperatures, which in Middle Tennessee usually means autumn or late spring rather than the middle of summer.
The two failures are applying too much and applying to a dirty or damp slab. Sealer is meant to go on thin. A heavy coat of film sealer traps moisture and turns white, and no amount of sun fixes it; it has to be stripped and redone.