Sealer

ICPI's section on what sealers are for opens with one sentence: "Sealers reduce the intrusion of water, stains, oils and dirt into the paver surfaces."

Reduce is a smaller word than seal. It describes less getting in, not nothing getting in, and it is the verb this definition is built on. The same document says most sealers change the look of the surface by darkening it and enhancing its color, and that some add a glossy sheen while others give a low sheen or a flat finish. The two families behind those finishes, film-forming and penetrating, are compared for finish and strengths in the sealing section of the paver cleaning page.

ICPI writes that sealers for concrete pavers can be either solvent or water based, and it names the chemistries it does not recommend for pavers or that are generally not used on them.

The list is short. Alkyds, esters and polyvinyl acetates are not recommended for use with pavers, and epoxies and silicones are generally not used on concrete pavers. What the carrier changes, how far a solvent or a water based product gets into the paver and what happens as the coat wears, is set out under what a sealer is carried in. Which carrier and which chemistry suit a particular surface is not something the word sealer answers: ICPI says the sealer manufacturer or supplier should be consulted before any sealer is used, and the product's own label carries it from there.

Natural stone uses a different word. The Natural Stone Institute writes that the sealing products used in the stone industry are impregnators, which "act as a repellent rather than a sealer."

The institute adds that sealing does not make stone stain proof; it makes stone more stain resistant. The Decorative Concrete Council of the American Society of Concrete Contractors draws a parallel line for decorative concrete, calling sealers scratch and stain resistant, not scratch and stain proof. Neither document is about concrete pavers, but both put the same kind of limit on the word that ICPI's reduce does, and that limit is why a sealer and waterproofing are different claims, taken up at does sealing make pavers waterproof.

Among the chemistries ICPI describes for pavers, acrylic and urethane leave a gloss on the surface, while silane and siloxane penetrate concrete and cure in its capillaries. Each has its own entry.