Q: What are the advantages/disadvantages of silane type sealers on concrete?
A: Silane is a topical concrete/cement surface sealer used to prevent water penetration under normal conditions. While laboratory analysis of the samples treated with silane show passable or good water sealing capacity, in the field it has been determined that water can still penetrate silane treated surfaces under static pressure such as applied for example by car tires. The reason for this phenomenon is in the mechanism of silane protection which (as opposed to coatings – physical barrier) relies primarily on the modification of substrate surface properties. Surface tension describes interfacial tension between a liquid and a solid. Increasing surface tension is a common means of concrete protection delivered primarily by silicone based breathable sealers. This system has a great water sealing capacity while allowing vapor to move relatively unobstructed. However when static pressure is applied, this barrier becomes insufficient. This has been established in laboratory by using pressurized testing techniques (as opposed to a column of water or submersion) and confirmed by monitoring the progressive movement of chlorides on decks treated with silane where the intermittent repetitive static pressure is exerted by simply driving over the wet chloride contaminated surfaces.
While it is important to keep the chloride contaminated water out of the concrete some moisture is essential to concrete integrity. If concrete is moisture deprived, porosity is open for the ingress of harmful pollutants and airborne chemicals such as carbon dioxide. In studies of marine concretes it has been shown that silane treated surfaces exposed to the same chemical environment carbonate much faster than the surfaces receiving no protection at all. The author's [of the study] supposition is that the loss of moisture on silane treated surfaces occurs either by hydrolyzing (splitting of water molecules consumed in the process of silane curing) or simple drying of vertical surfaces due to reduced water ingress, allows more air/carbon dioxide to penetrate and to attack the free lime (CaOH) in concrete by forming carbonic acid. This process known as carbonation leads to the loss of pH increasing potential for corrosion of the embedded reinforcement.
Silanes are inherently tricky to apply correctly. As some outside moisture is consumed in the process of silane curing it is important that proper amount of moisture is available at the time of application. It can not be rainy or wet and also it can not be overly dry. The concrete has to have an appropriate moisture content and it has to be just so only slightly humid and mild. Improper curing – too fast or too slow or incomplete – interferes with the results.
To produce optimum results for most commonly available silanes the quantity applied should be sufficient. In many cases applying a sufficient quantity of any particular silane means to initially over-apply it. Containment of the treatment area must be maintained to prevent toxic run off.
Max M., Manager, Surtreat Holding, LLC contact
Surtreat Holding, LLC 437 Grant Street, Pittsburgh, PA 15219; 412.281.1202, official website www.surtreat.info
Max Merzlikin, Surtreat Holding, LLC 2015