Stamped Concrete Sealer
Sealing Stamped Concrete
“Know what you’re sealing over.”
Most manufacturers of acrylic sealers recommend re-sealing with the identical product that was used originally or not re-sealing at all, for concerns of incompatibility or weakened bond strength. For your projects that you know have been sealed last with something other than what is currently available, please contact your supplier or the manufacturers of the current product as well as the product last used (if used successfully). It will likely be recommended that you first test a small area and allow it to weather for a while. If the new and old sealers do not bond to each other with enough strength or if they are not bonded strongly to the concrete, that bond will be compromised under the pressure of moisture, sun, and time – sometimes resulting in a whitened film. Evidence of a problem is most likely to develop within a month but will occasionally take longer to identify itself so please allow enough time to pass prior to conclusion of your test results. There is still no agreed reason between chemists and authorities as to why this occurs but the consensus is that it is most directly related to film thickness and moisture vapor pressure, which is why most problems arise shortly after, or during, periods of excessive precipitation.
It is also debated whether or not there is, in fact, an identifiable compatibility issue between different acrylic sealers with different resins and different chemistry. There has been no definitive testing that suggests there is a specific incompatibility that results in consistent failure or delamination of any one acrylic sealer when used in conjunction with any other different, particular sealer. However, all resins at various thickness will react to and change differently with their environment. Since two resins may not always respond similarly to things such as sunlight, moisture vapor transmission, foot or vehicle traffic, freeze/thaw cycles, and simply aging, they may begin to “disagree” with each other and result in an overall or partial failure of the system. For example, styrene acrylics are less UV stable than some other acrylic co-polymers or pure acrylics. If a styrene acrylic has been subjected to a year of UV exposure it can discolor and also begin to degrade. Other resins like methacrylates will be less responsive to change from UV light but also have a different hardness to the cured film. If you were to apply a film of a hard, UV stable sealer, over a degrading sealer whose constantly changing from UV, the two will come to odds with each other and potentially delaminate from one another. In an extreme comparison, imagine how freezing rain tenaciously binds to your windshield. It can be very difficult to scrape the sheet of ice away in the morning. However, as the environment changes from cold to warm, the sheet of ice responds by melting and your glass windshield is unchanged. The bond line between the ice and glass is weakened and the sheet of ice breaks away. Many environmental changes can trigger similar responses between two types of sealer, though usually over a longer time frame and typically with results that don’t completely repair themselves as easily. At the same time, keep in mind that this type of failure will not always be the result of using different sealers with one another and it is possible, in fact widely maintained, that even failures that seem to be the blame of incompatibility are still likely related to film thickness and moisture. One thing is for sure, it is FAR more rare to see a sealer failure occur with the exclusive use of a single product applied in very thin coats. This seems to hold true for re-sealing as well, as long as the surface is clean and very dry before the re-seal coat is applied (again, very thinly). We now understand that changing products too often can only increase the likelihood of problems arising if re-sealing with a new sealer.
For a better grasp of how sealers may work together, it is important to know the product you are re-sealing over. With some help from your supplier or manufacturer, and a light education in general sealer chemistry, most concerns of incompatibility can be reduced and often eliminated. Always be sure to keep in mind the specific application rate of the product you are using along with proper conditions of the substrate over which you are applying it. If you have questions about the chemistry of a product that has been used in the past and you would like to re-seal it, please contact Sealant Depot or the product’s manufacturer. If the original product is not readily available and/or you would like to use a different product to re-seal with, there are few recommended practices. Namely, it is best to use the most similar product available to you (use like resins, do not mix different resins i.e. styrene acrylics, methyl methacrylates, or pure acrylics) and perform a reasonable-sized test area (one that is large enough to yield true results, and also small enough that it can still be stripped if necessary). For help in choosing the most similar product available, call your local supplier. They should be able to help you. If not, we at Sealant Depot will do our best to help you as well.
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