Anne Sullivan wrote:
>Question -- howdoes the depth of
penetration differ between the waterborne and solventborne water
repellents?"

A couple of factors affect penetration, from the formulation side of the
equation. (That is, excluding those substrate factors that determine
substrate porosity, such as pore size).

The first is surface tension. Basically this describes the resistance of a
substrate to being wetted by a particular liquid. The surface tension of
water is typically about 3 times higher than that  of most common solvents
used in sealers. This tends to make water less efficient at penetrating
small pores and capillaries. Surfactants are often used, essentially
high-tech soaps, which reduce sealer surface tension, making the difference
much less dramatic. Surface tension is not a big factor on very porous
substrates like common brick or concrete masonry units. It can be a
significant factor on dense substrates like high-strength concrete, and
harder stone.

The second factor is molecular weight, or how "big" the active ingredients
are in their basic chemical structure. The acrylic resins used in acrylic
sealers may typically have a molecular weight of 25,000 to 50,000 or
higher. Big molecules can't "fit" into the smallest pores and capillaries.

Oils can have molecular weights on the order of 1000 or so. Silanes may be
around  2500. Siloxanes, I am told, can be anywhere from 2500 to 25,000.
Oil penetrates well, silanes do as well. The bigger the molecule, the less
likely it is to penetrate.

So water vs. solvent is only part of the story. We tend to favor different
treatments for different substrates, using blends of low, medium and high
molecular weight materials. We find waterborne performance adequate for
most applications, and compelling when lots of people are going to be
around to complain about solvent odors.

We still use solvent-borne sealers on our bridge deck work, though.

Mike E.