KEIM silicate stains and finishes have moisture vapor permeance (MVP) equal to that of the mineral surface where applied. This effectively means that silicate finishes do not inhibit the diffusion of water vapor. Moisture contained in the wall assembly may diffuse outward without resistance. This helps keeps walls drier, preventing structural damage and mold growth.
Allowing moisture vapor to escape, is essential when finishing building envelopes that were built prior to the general use of moisture barriers, as found in historic structures. Historic masonry structures often are plagued by rising damp and other moisture problems, and painting with barriers like ordinary paints, can cause internal wall damage and growth of mold.
Use of mineral silicates is widely recognized as the ideal way to finish historic masonry to allow these walls to seek an ideal moisture balance.
KEIM Silicate benefits at a glance...
- Silicate finishes do not inhibit moisture vapor from diffusing out of walls
- Walls maintain an ideal moisture balance, both inside and outside
- Will never blister like latex or acrylic paints
- Drier wall assemblies are less prone to rot and mold
- Limits surface condensation
- Surface dries out much quicker than latex and acrylic painted surfaces
- Weatherproof finish provides optimal protection against water intrusion and freeze-thaw damage
- Highly resistant to algae, fungi and mold
What is vapor permeability?
Vapor permeability, or more commonly referred to as breathability, is a building material’s ability to allow water “vapor” to pass through it. Don’t confuse this process with the concept of holding out bulk water. Bulk water is moisture in liquid form and vapor is a gas, and how each moves in a wall is significantly different. When you have moisture vapor in your wall, a single molecule can break away and escapes by diffusion. Materials that allow these vapor molecules to pass unhindered, are considered to be vapor permeable.
Why is vapor permeability important?
Because wall assemblies, both historic and modern, do get wet. Roofs can leak, condensation occurs, plumbing leaks, construction materials are installed wet and internal moisture loads can be very high. And when walls get wet they require a way to dry out. When a wall can’t dry out, it becomes vulnerable to moisture-induced damage including mold and rot.
How is permeability measured?
There are two standard laboratory measurement tests, which are described here. Standard lab tests are sound measuring tools, and can be good predictors of what happens in the real world. The Laboratory Test – ASTM E96 Moisture vapor transmission rate (MVTR) is the measurement referenced in many building codes. This test method measures how much moisture vapor is allowed to pass in a 24-hour period. This measurement can be impacted by vapor pressure, so when you want to compare materials you adjust the measurement for vapor pressure across the sample to get the moisture vapor permeance (MVP). The unit of measurement for MVP is perms. ASTM E96 can be used to give materials a relative rating to show how they allow moisture vapor to diffuse. The higher the number, the more moisture vapor the material will allow to pass, and the material allows for better drying.
This type of data can be used to compare a material’s moisture vapor transmission property but does not necessarily indicate how that relates to a wall system’s performance in the “real world.” KEIM chemists perform a series of tests, from ASTM standard tests to practical evaluations to field studies and modeling recommendations for the building industry.