When introduced in the 1970s, penetrating sealer formulations were 100% silane.
Silanes in and of themselves are not a volatile organic compound (VOC), but they contain VOCs. For example, a 100% silane formulation contains about 350 grams/liter.
In 1998, to combat air pollution, EPA’s Architectural and Industrial Maintenance (AIM) Coatings rule lowered the amount of VOCs that sealants may emit to 800 grams/liter of solvent/bucket. In 2005, the federal requirement became 600 grams/liter and, in the 13 Ozone Transport Commission states, 400 grams/liter.
The VOC content of silane-based penetrating sealers can be lowered via emulsification into water using special surfactants (waterborne) or by adding non-VOC (also called exempt) solvents (solventborne).
Waterborne formulations typically contain 10% to 40% silane. Solventborne formulations contain 20% to 100% silane. Depending on your state’s requirements, manufacturers can make solventborne formulations of 100 grams/liter VOCs with 40% silane solids.
Because there are advantages and disadvantages to each, what’s right for your application depends on your budget and goals.
Solventborne silanes dissolve their way through some dirt, grime, and rubber. Waterborne formulations don’t, so they require a cleaner substrate to achieve good penetration.
Silanes mixed with water don’t penetrate as deeply, which you should keep in mind if your goal is to protect steel rebar.
Deeper penetration (¼ inch-plus)
Faster dry times
Easy to apply
Less penetration (less than ¼ inch)
Lower VOCs than solventborne are attainable
Slower dry times
Not recoatable with itself