There are many sealers on the market. Most are to protect the surface from water or moisture intrusion. There are sealers that are designed to enhance the beauty of the surface or add gloss or a “wet look”. Sealers can be categorized as surface or penetrating. Surface sealers are usually silicone based and last from as little as a few months to a few years. The reason is that silicone is a larger molecule and therefore sits closer to the surface. Since UV light is what attacks these sealers then the larger molecule silicones will break down first. Penetrating sealers are usually silane and or siloxane based. This is a smaller molecule and therefore penetrates further into the surface before forming the hydrophobic barrier. Silicones are usually less expensive than silanes so how long you want the sealer to last is important question. The substrate is the next most important variable. How porous is the material? This will determine how deep a penetrating sealer will go. This is a two edged sword, the material will last longer as it penetrates deeper but it won’t seal the surface from staining. The primary function of a good penetrating sealer is to keep moisture out of the wall cavity. This is where the water can do the most damage. It can find a way into our homes damaging drywall and carpet but what we don’t see is usually worse. Degradation of wood framing, damaging electrical outlets and shorts and growing of molds are just a few examples of damage water can do as it enters the wall space. We must be aware however; that penetrants are just that, they will not protect the surface from staining unless built up to the surface with subsequent coats. The proper way to put on penetrating sealers is to make sure that new concrete, masonry or stucco is cured and “thirsty” enough to accept the chemical. Since the chemical is now carried by water this is pretty easy to test. The literature usually says to wait the initial 28 day cure period before application. The problem with this is that your wall can get badly stained in 28 days. My advice is to gauge the weather against how dry or “thirsty” your substrate is and then make your own decision as to when to apply the sealer. These sealers need to form a barrier so there needs to be enough material put on to make that barrier. This usually means we put on a “flood coat” and then brush off any excess material. From a chemical engineering perspective the exact proper way is to apply a very light “fog coat” of material to “open the capillaries” of the wall. Then come back immediately and flood the surface to insure the wall accepts as much material as possible. Most often people just use a pump up “bug sprayer” and fill the wall with material until it runs and then back roll or brush off the excess. There is a very important caveat here though, when it is hot dry or windy and when doing flat surfaces it is critical to get the right amount of sealer on. If there is too much material and the substrate cannot accept the chemical and it will be deposited on the surface. This will result in a residual sticky material left on the surface to catch dirt, leaves, foot prints or whatever blows by. So try to do the job in the morning before the sun is too hot and don’t use these sealers when it is windy for this reason and you won’t get an even application. If you find that there is residual material left on any surface you can cut it off with a solvent. Paint thinner or any other solvent can be put on a rag and cut the material off the surface. Don’t worry, the rest of the material will still be in the wall as long as you don’t let the solvent penetrate. Just use it to wipe off the excess chemical without having it drip off the rag. It will evaporate very quickly and be gone leaving your sealer intact. Remember to cover all windows and frames as these penetrants can etch glass. Please read all the safety instructions before use. Think about the material you are putting the sealer on. Is it a flashed brick with very little suction? Then the material will go in very slowly or not at all. Very porous products like a Concrete Masonry Unit (concrete block) are very porous and will therefore use a lot of product. Merlex makes a penetrating sealer call Micro-Seal II that is less expensive than any other penetrating sealers I have found. It is a great product and is warranted for 10 years! The literature will show how much sealer will cover different materials. Logic dictates that the more “open” the surface the more material will go in and the further it will go in. The less “open” the substrate the less the material will go in and will therefore go further in terms of coverage. You can use these products on brick, block, stone, concrete, stucco or any other cementitious substrate. I have found over the years that silicones are used because people don’t know about silanes. Why would you use a sealer that will last 3 years at best when you can use penetrants lasting 10 years? The price difference is not that much. I guess if it is model complex of homes or a case where a year of protection is fine then the less expensive silicone will fill the bill. I talk mostly to homeowners that are doing their own homes and want maximum protection for the longest period. Go with a good penetrating sealer and take all the precautions talked about here and you will protect your surfaces without having to reapply every few years.
