The Concrete Network

First, the good news: Deicing salts have no direct effect on sealers. In fact, concrete sealers of any type have been proven to increase the lifespan of salt-treated concrete three to five times! Now the reality: Sealers for decorative concrete often fail in areas where deicing salts are applied or that receive drip-off from parked cars. It's not the salt, though, but rather what the salt is doing that causes the sealer to fail.

Salt chemically reduces the temperature at which water freezes. When salt is applied to a sealed decorative concrete surface covered by snow and ice, it causes melting and turns the frozen water into a liquid that is now able to migrate into the concrete. This salt-rich water (brine) goes through many freeze-thaw cycles as environmental conditions change (i.e., more snow falls, the sun comes out, more salt is applied, the temperature changes, etc.). So instead of one freeze-thaw cycle per day (or season, the farther north you live), it's possible to have hundreds per day when salt is used. During each cycle, the water expands as it freezes and thaws as it contracts. The problem is that while sealers help to retard moisture movement, they do not stop it completely. So as the saltwater passes through, under and all around the sealer, the water is expanding and contracting, and eventually the sealer will fail.

Think about what happens when you bend a steel wire. The first time, not much. But when you bend the wire 50 times, it's likely to snap. A sealer can only take so much pressure from water expansion and contraction before it snaps and pops off the surface. The same process is what causes the top layer of concrete to pop off (commonly referred to as spalling or surface delamination) in high-salt-use areas.

The best offense against sealer failure due to deicing salt use is a good defense. In areas with severe winters, some contractors use a combination of sealers to fight the effects of deicing salts. They start with a penetrating sealer (silane, siloxane or silicone) that fills the concrete pores from the bottom up. Then they apply an acrylic sealer for decorative concrete that creates a membrane from the top down. This systems approach costs a bit more, but when faced with stripping and resealing, it may be well worth it.

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Author Chris Sullivan, ConcreteNetwork.com technical expert and vice president of sales and marketing for ChemSystems Inc.


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