Penetrating repellent or film-forming sealer?
Silane and siloxane repellents
Silane molecules are small. Small enough to penetrate deep into the concrete and bond within it. The surface keeps its natural look and stays vapor-permeable. Siloxane molecules are larger and penetrate less deeply; blended products combine both. Either one reduces how much liquid water and chloride the concrete absorbs, which is why they're a common choice for exterior driveways, walkways, and parking structures. Neither one waterproofs the slab. Rain still beads and rolls off, but an active crack or a joint under hydrostatic pressure will still let water through.
Acrylic and other film-forming sealers
Acrylic sealers are the standard choice over stamped and stained exterior concrete because they enhance color and let you choose a sheen from matte to high gloss. Water-based and solvent-based versions cure differently and aren't always interchangeable. ARDEX CG Concrete Guard, a high-solids waterborne acrylic from the ARDEX line we're factory-trained on, is one option we use here, not the only acrylic sealer on the truck. They're recoatable, but they have real limits: lower chemical resistance than a coating like epoxy, some scratching and softening from solvents, and a tendency to go slippery when wet at higher gloss levels.