Sealing brick isn’t a requirement, but there are many benefits that come along with using a good brick sealer. Brick sealers help to extend the life of the bricks, reduce deterioration caused by surface abrasion, reduce deterioration caused by water absorption, and reduce the growth of mold, mildew, and efflorescence.
There are three primary types of sealers used to seal brick: silicate sealers, Silane-Siloxane sealers, and acrylic sealers.
- Silicate Sealers: Silicate sealers penetrate into the brick where they chemically react with the free lime and calcium to form a calcium silicate hydrate structure within the pores. Silicate sealers reduce the size of the pores, therefore increasing strength and density. Silicate sealers are great to use on weak and deteriorating brick, but when applying a silicate sealer to brick you need to do so with caution. Brick are very porous and it is very easy to over apply a silicate sealer to brick. When a silicate sealer is over applied to brick, white crystals can form on the surface. These white crystals can’t be removed unless you grind or remove the surface of the brick. If you are going to use a silicate sealer on brick you want to use a very diluted lithium silicate and apply thin coats. When properly applied, silicate sealers help to increase the surface strength and density of the brick, and reduce deterioration caused by surface abrasion and age.
- Silane-Siloxane Sealers: Silane-Siloxane sealers are considered to be the best brick sealer. They are breathable, water repellent sealers that chemically react to form a hydrophobic barrier within the pores. They won’t change the look or color of the brick, and they don’t leave behind a surface film. Silane-Siloxane sealers help to reduce water absorption by up to 95%, and reduce deterioration caused by water absorption such as cracking, spalling, pitting, and staining. Silane-Siloxane sealers also help to reduce the formation of mold, mildew, and efflorescence.
- Acrylic Sealers: This is where it gets tricky. Acrylic sealers are the only type of coating that should be applied to brick because brick needs to remain breathable and acrylic sealers are breathable coatings. Acrylic sealers are sensitive to moisture however so if moisture is present in the brick, delamination (white hazing) may occur. If you require a wet look, colored, or high gloss finish and want to use an acrylic sealer, consider first applying the acrylic to a test area and leave it on for 1-2 weeks.
Using a Combination of Brick Sealers
It isn’t uncommon for people to use more than one brick sealer. It is important to make sure that if you use two different types of brick sealers, you apply them in the right order.
- Silicate and Silane-Siloxane sealer: If you use a silicate and a Silane-Siloxane sealer you want to apply the silicate sealer first and then the Silane-Siloxane sealer 7+ days later.
- Silicate and Acrylic sealer: Silicate sealers reduce pore size and acrylic sealers need available space within the pores to bond. A test area should be applied first to make sure that the acrylic sealer can still bond once the silicate sealer has been applied. Acrylic sealers should be applied 7+ days after the silicate has been applied.
- Silane-Siloxane and Acrylic Sealer: A Silane-Siloxane sealer should be applied before an acrylic sealer is applied. If you are combining this type of sealer you need to make sure they are compatable. A solvent based Silane-Siloxane sealer should be applied before a solvent based acrylic. You can also apply a solvent based acrylic over a water based Silane-Siloxane sealer. You can not however apply a water based acrylic over a Silane-Siloxane sealer because Silane-Siloxane sealers are water repellents and will repel water based coatings.