Many companies are now promoting the pre-sealing of stone products at the point of fabrication. Although this may sound attractive to an uneducated buyer, this is more of a marketing ploy than a true consumer benefit for reasons that will become obvious below. Sealers come in two basic forms, a topical or penetrating sealer. A topical sealer is just that, a clear protective coating on the exterior of the stone that blocks potential substances from entering the stone surface. A penetrating sealer, penetrates the stone and actually acts as a barrier to staining by not allowing any substances to occupy the same space. One benefit of a penetrating sealer over a topical sealer is its ability to hold up to wear and tear and heavy traffic better.
Penetrating sealers also can hold up for 15 years or longer and comes in two forms, water based or solvent based formulas. Many of the water based sealers on the market will allow water vapor to transfer through the stone after installation allowing the stone to be pre-sealed at the factory. The benefits to having a stone pre sealed prior to installation are to prevent the color pigmentation from grout staining the stone, staining from occurring during installation, and to assist with ease of grout cleanup. Now with the benefits being explained here are the challenges that occur with sealing prior to installation.
The stone has to be completely dry prior to application. In a quarry and manufacturing process this is very difficult due to the amount of water required for fabrication and cutting of the stone. Once cut, the stone needs to completely dry for several days prior to applying the sealer. During the manufacturing process if the sealer is put on while the stone is still wet, the benefits of sealing the stone will be lost. The reason for this is because sealers work by occupying "space" that would otherwise allow other substances to absorb into the stone. If the stone is not dry, the sealer has an extremely difficult time "bullying" past the water. Thus when the stone finally does dry, the sealer will not have taken up the space occupied by the water molecules and the stone will not be properly sealed. Our experience working in and around stone fabrication facilities is that they are not dry enough to allow the stone to properly dry allowing a sealer to be applied at most factories. In addition, the sealers need to dry several hours between any second or third coats being applied and a large dry and clean space would be required to lay the stone out to let it dry; the stone would have to remain in a dry and clean space for over three days. This would be a very time consuming and costly process. The region in which the stone is produced is very cold and wet during winter months and wet and humid during the summer. In addition, if the stone has not properly dried prior to the sealer application it can cause some discolorizaton to occur and for all of the above reasons we do not believe pre-sealing the stone at the factory would be as effective as sealing the stone after installation.
Even if the stone is pre-sealed at the factory, once the floor is installed and grouted, a sealer would again need to be applied after grouting. To avoid any challenges, the same sealer used by the factory during the pre-sealing process would also have to be used after grouting to avoid any chemical reactions that could damage or discolor the stone. This would need to be conveyed to each installer to make sure they were familiar with working with the brand used by the factory (is it available in the US?) and since there are various qualities of sealers on the market, I would want to verify a factory is using the best sealer for the end use and application rather than a less effective cost efficient sealer. In addition, if the stone is sealed prior to installation, the stone transportation and installation process increases the likelihood the sealer surface would be altered. Examples are when packaging the finished side of the stone are usually packaged facing each other. If they rub or scratch, it becomes necessary to match the factory sealing and look which becomes more difficult.
Even though many vendors have great relationships with their factories, I believe it is in everyone's best interest to control the sealing of stone from our end here in the US especially since regardless of any pre-sealing, the stone is going to have to again be sealed after grouting. My experience demonstrates better results can be obtained by first applying one coat of the penetrating sealer that will be used for final sealing after the stone has been installed and allowed to dry and prior to grouting. After the stone has been grouted and allowed to dry (a minimum of 48 hours depending upon the climate and other factors), the same sealer is once again applied. Depending upon the porosity of the stone usually one or two applications are required with the sealer being allowed to dry a minimum of several hours between applications (up to three total applications counting the pre grouting coat). However, we always recommend following the sealer's manufacturer directions for application. Since the purpose of the sealer is to "occupy space" this allows the sealer to properly work its way into the stone and helps prevent staining. Since the cost of the sealer whether applied at the factory or after installation is going to be similar, we find it is ultimately safer, more cost effective, and achieves better results if the sealer is applied once the stone is initially installed. My experience is also manufactures who promote pre-sealing the stone at the factory often use inexpensive products that will need to be sealed again shortly after installation and is promoted for marketing purposes. Regardless, any stone will need to be again sealed in future years following the manufacture recommendations.
For clients desiring little to no after market care, porcelain products are a great alternative. Porcelain due to its manufacturing process is usually impervious to staining and does not require sealer protection or after market care. Ceramic tiles with the ability to absorb more water usually require a protective sealers since the glazes are continually changing. Due to the incredible number of variables in manufacturing ceramic tile, I always recommend consulting with the tiles manufacturer or company selling the tile to determine the manufacturer's recommendations on how to best to protect your investment. In all cases it is usually always necessary to seal projects using sanded and un sanded grouted areas, however, epoxy grouts usually do not require sealing.
