Silane and siloxane

Silane and siloxane start as two differently sized molecules doing the same job.

ICPI describes silanes as the simpler form: when exposed to moisture they begin linking to other silanes, and siloxanes do the same linking together. Both become a polymer, curing as a film in the capillaries of the concrete rather than as a coat on its face. Silane's smaller molecule penetrates farther into the concrete than siloxane's, but ICPI says silanes are more volatile, tending to evaporate until they bond to the paver, so silane sealers generally require a higher percent of solids to counteract that.

Curing inside the pores rather than on the surface changes both what the finish looks like and what it does with moisture.

The hydrophobic barrier keeps moisture from entering while letting the concrete breathe, or release water vapor. Silanes and siloxanes initially enhance colors, ICPI says, and produce a flat, no-gloss finish, unlike the gloss an acrylic or urethane leaves. Whether a matte or natural-look product is available as a choice is answered at is there a matte or natural-look paver sealer. A barrier that keeps moisture out is also not the same claim as waterproof, the question taken up at does sealing make pavers waterproof.

The same chemistry that keeps water out has one stain it does not resist on its own.

ICPI is direct about it: silanes and siloxanes do not resist penetration of petroleum stains unless they have additives specifically for that purpose. A barrier against water is not, by that fact alone, a barrier against an oil drip on a driveway. Whether a given product carries such an additive is printed on its label, not implied by the chemistry name.

Two more things about this chemistry reach past the data sheet: where ICPI says it helps, and a maker's word for the way a sealer breathes.

ICPI writes that silanes and siloxanes give additional protection to pavers subject to salt air and are useful around pool decks against chlorine, uses covered where the paver cleaning page compares the sealer families. The property that lets the concrete release water vapor goes by another name on a maker's label: Techniseal calls its protectors microporous, meaning they let moisture out, a word with its own entry at microporous. Whether a surface already carries a sealer, of this chemistry or another, is its own question, answered at how to tell if pavers were sealed before.