A breathable sealer is defined as a sealer that allows for moisture vapor to release out through the pores of the substrate. A non breathable sealer is a sealer that traps moisture vapor below the surface.
When should a breathable sealer be used, and why is it important?
There are certain substrates that require the sealer to be breathable. If a non-breathable sealer is applied to a substrate that requires a sealer to be breathable, the substrate can start to deteriorate from within the pores and the non-breathable sealer will eventually fail.
Take brick for example. Bricks need to remain breathable. If a non-breathable sealer is placed on the surface of the brick and water or moisture is or becomes present within the pores, the non-breathable sealer will trap the water and moisture below the surface in the pores of the brick. As pressure builds up below the surface, the water and moisture will start to cause the brick to deteriorate (come apart) from within the pores. Eventually, once enough water and moisture builds up, the non-breathable coating will fail and start to peel up. In severe cases, the brick will start to chip away and fall off with the non-breathable sealer.
There are a few types of substrates that need to remain breathable, including:
- Red clay bricks
- Clay roof tiles
- Natural Stone
- Exterior concrete
The only time a non-breathable sealer should be used is on interior poured concrete floors that require a vapor barrier. Vapor barriers are often requires on floors that are in a living space, or will be finished with wood floors. Non breathable sealers are typically epoxy and urethane coatings, and paint.
Types of Breathable Sealers
There are several types of sealers that are classified as being breathable:
- Silicate Sealers: All silicate sealers are breathable. Silicate sealers penetrate into the surface of the concrete where they chemically react to form a hardened crystalline barrier within the pores. Sliicate sealers reduce the size of the pores, but they don’t close the pores. Concrete sealed with a silicate sealer will remain breathable once sealed.
- Water Repellent Sealers: All water repellent sealers are breathable. Water repellent sealers (Silane Siloxane sealers and siliconate sealers) penetrate into the surface of the concrete/masonry where they chemically react to form a hydrophobic barrier within the pores. Water repellent sealers are designed to repel water off the surface and reduce deterioration caused by water absorption. The hydrophobic barrier within the pores is breathable and concrete/masonry sealed with a water repellent sealer will remain breathable once sealed.
- Acrylic Sealers: Most acrylic sealers are breathable, but not all. Breathability is a little more complex with acrylic sealers. When it comes to acrylics there are different types of acrylic sealers and different levels of solids.
- Type of Acrylic Sealer: Pure acrylic lacquers and acrylic co-polymers are breathable acrylic sealers. Acrylic latex sealers are not breathable however. Acrylic latex sealers really aren’t sealers, they are more like a paint. When using an acrylic sealer, you want to look for a pure acrylic or an acrylic co-polymer.
- % Solids: The higher the solids, the lower the breathability. With acrylic sealers, if a 25% or lower solids solution is considered to be very breathable. Once you start getting up to 30% solutions and higher, the acrylic becomes less breathable and issues start to occur with delamination and coating failure. 15% solids solutions tend to be very low gloss, almost matte, while 20-25% solids solutions have a low to high gloss.
- Number of Coats: Acrylic sealers are not designed as a high build coating. They are designed to be applied in thin coats. 1-2 coats is typical, but an acrylic sealer should never exceed 3 coats. As more coats are applied, the breathability is reduced. If you have questions, it is best to contact the manufacture of the acrylic you are considering.
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