Before you use a sealer on your brick, masonry or concrete, you should know and understand the different chemistry and how it will work on your particular project.
Penetrating Chemically-Reactive Sealers
1. Silane / Silane-Siloxane Sealers – Silane sealers have small molecules and are slow reacting; allowing them to deeply penetrate the concrete. The concrete must be thoroughly saturated with a high solid Silane to be adequately sealed. The main problem in the industry is that the products are used with too low of a spread ratio and do not have a high solid (active ingredient) content. A very heavy saturation on the surface is required to get an adequate seal. They work very well for very porous substrates and for protecting vertical surfaces from wind-driven rain if they are applied correctly. These sealers protect against mold and mildew and efflorescence. If applied correctly, they are the most costly of the penetrating sealers as multiple applications are necessary. Silane or silane-siloxane sealers cannot be used on newly placed concrete. Surfaces must be 28 days old and/or fully cured before using them.
Silane / Silane-Siloxane Sealers do not bond to the substrate. They fill the open pores of the substrate, filling it to prevent water penetration, but they break-down over time due to heat, humidity, cold weather, etc. and need to be completely redone about every 5 years. They work especially well on brick, masonry and split-face block. (Link to SealGreen Brick and Stone Sealer)
2. Silicate Concrete Sealers - These are chemically reactive, penetrating chemicals that permanently bind to the silicates in the concrete. The concrete must be removed in order to remove the sealer. Silicates are easy and inexpensive to make. However, there is no standard and the quality of the sealer is very dependent on the manufacturer and their ethics. Silicates have the smallest molecules of the penetrating sealers and as such go very deep into the concrete. Technically silicates should not be called "concrete sealers" but rather densifiers or hardeners. In order to seal the surface, you must build the sealer from the bottom of the concrete to the top. This requires a lot of product and many applications – sometimes even working the product into the concrete. Most installers who use silicates as sealers do not apply the product properly so an adequate seal is not achieved. Silicate sealers are the lowest price sealers of the penetrating sealers. They cannot be used as a cure and seal on new concrete because they do not maintain the required moisture and temperatures as they do not truly seal the surface. They can be used on new concrete to densify, harden or strengthen the concrete.
3. Siliconate Sealers – Siliconate sealers are versatile sealers that can be used on almost any concrete surface. These sealers work by creating a permanent chemical change within the concrete. This chemical reaction inside the open pores of the concrete creates a gel, which hardens, chemically bonding to the concrete and creating a “plug” in the pore. They are inside the concrete as long as the concrete exists. Siliconates have the largest molecules of penetrating sealers and react quickly which effectively seals the surface of the concrete offering more surface protection while maintaining the breathability of the concrete. Siliconate sealers are the perfect choice when your primary objectives are reducing moisture absorption, reducing freeze/thaw damage and reducing stain penetration. Siliconates dry within the concrete and do not change the appearance or the texture of the concrete surface. They can also be used as a cure for freshly poured concrete. They cure by retarding moisture while allowing the concrete to breath. Siliconates have multiple applications – they can be used on bare concrete walls or stucco to keep moisture from soaking through paint and to allow the paint to last longer. Siliconates can be used on sidewalks, driveways, parking lots, porches, pool decks, retaining walls, patios, etc. to reduce cracking, staining, and freeze/thaw damage. Overall, this is the sealer we believe works the best for the majority of applications on broom or trowel finish concrete. (Link to SealGreen Concrete Sealer)
There are other types of sealers available on the market but these are basic types most often used on exterior concrete and masonry. If in doubt – call and talk to a knowledgeable person in the sealing industry to help you decide which sealer to use.