The short answer: sometimes, and the type matters more than the decision
Sealing is not required after pressure washing. Plain broom-finished concrete does fine for decades without it in Southern California, because we do not have the freeze-thaw cycles and road salt that eat concrete in colder places. A clean, unsealed driveway is a perfectly good outcome.
Sealing earns its cost in specific situations: stamped or colored concrete, exposed aggregate you want to look rich, driveways with cars that drip, and surfaces near the coast. The bigger choice is which kind of sealer, because the two main families behave very differently.
Penetrating sealers vs film-forming sealers
Penetrating sealers, usually silane or siloxane based, soak into the concrete and react inside the pores. They make water and many stains bead up instead of soaking in, but they leave almost no visible film. The concrete looks the same, does not get slippery, and the sealer does not peel. They are the low-drama choice for plain driveways and walkways.
Film-forming sealers, usually acrylic, sit on top as a thin coating. They deepen color and can give a wet look or a sheen, which is why they are popular on stamped and colored concrete. The tradeoffs are real: they wear in traffic lanes, can turn cloudy if moisture is trapped, can soften under hot tires, and need recoating on a regular cycle. Once you start with a film sealer, you are committing to maintaining it.
Where sealing pays off
Decorative concrete is the clearest case. Stamped and colored driveways are usually sealed from the start, and keeping that sealer healthy protects the color. Exposed aggregate gets a big visual boost from a sealer that brings out the stones.
A penetrating sealer is also worth considering if a car drips oil or you park a work truck on the slab. It does not make concrete stain-proof, but it buys time to clean a spill before it soaks in. Near the coast, damp marine air and shaded spots grow film faster, and sealed concrete tends to clean up more easily.
When sealing is a waste of money
Sealing over stains locks them in. If an oil spot or rust mark is still visible after cleaning, sealing will preserve it under the coating. Clean first, accept what is left, then decide.
Sealing also does little for a driveway that is cracked, spalling or crumbling. That concrete needs repair. And a plain driveway that just gets dusty from Santa Ana winds and leaves will not look much different sealed versus unsealed. A yearly cleaning will do more for it.
Timing after pressure washing
Concrete has to be fully dry before sealing. Water trapped under a film sealer is the main cause of white, cloudy patches. In hot, sunny Valley weather the slab may dry within a full day. In shade, or when the marine layer hangs around, give it longer. A simple check is to tape a square of plastic to the surface for a few hours. If moisture collects underneath, wait.
Avoid sealing right before rain, which matters most in the rainy season from about November to March. Follow the temperature range on the product label, and avoid sealing in the hottest part of a summer afternoon, when the sealer can flash dry unevenly. If white efflorescence is present, treat it before sealing or it will end up under the coating.
Slip resistance and upkeep
Glossy acrylic sealers can be slick when wet, which matters on sloped driveways, pool surrounds and front steps. If you choose a film sealer for those areas, ask for a slip-resistant grit additive mixed in. Penetrating sealers keep the original texture, so they do not change traction.
Every sealer wears. Penetrating types last longer but stop beading water eventually. Film types show wear in tire paths first. When water stops beading or the finish looks patchy, it is time to clean and reapply. Cleaning sealed concrete calls for lower pressure and milder chemistry so the coating is not damaged.
If you are unsure, start small. Seal a single area, such as the parking pad where the car drips, and see how you like it through a rainy season. That tells you more about the look, the traction and the upkeep than any product label.
Key points
The short answer: sometimes, and the type matters more than the decision
Sealing is not required after pressure washing. Plain broom-finished concrete does fine for decades without it in Southern California, because we do not have the freeze-thaw cycles and road salt that eat concrete in colder places. A clean, unsealed driveway is a perfectly good outcome.
Penetrating sealers vs film-forming sealers
Penetrating sealers, usually silane or siloxane based, soak into the concrete and react inside the pores. They make water and many stains bead up instead of soaking in, but they leave almost no visible film. The concrete looks the same, does not get slippery, and the sealer does not peel. They are the low-drama choice for plain driveways and walkways.