1. A winter storm dumps snow on your driveway or sidewalk.
2. The sun comes out and melts what you haven’t shoveled away.
3. The meltwater soaks into the concrete’s microscopic pores.
4. Temperatures drop, and the water in the concrete freezes and expands. As ice, it increases in volume about 9 percent. That stresses the concrete from inside.
5. Temperatures rise and the ice melts, relieving the internal pressure. But the concrete is slightly weakened.
6. The cycle repeats. Renewed pressure causes microscopic cracks that let in more water, which speeds up the process.
7. The cracks don’t stay microscopic.
1. Along with shoveling your drive or sidewalk, you may have put de-icing salts down to help melt the snow and ice. You could also have brought de-icing salts home caked up in the wheel wells of your car. It drops onto the driveway.
2. The de-icing salts increase the frequency of freeze/thaw cycling by creating more meltwater faster.
3. In addition to more freeze/thaw, the meltwater carries dissolved salts into the concrete.
4. The salty meltwater contacts the reinforcing steel rebar embedded in the concrete.
5. The water rusts the rebar, and the salts dramatically increase the reaction, causing the bars’ surfaces to expand, further stressing the concrete.
6. Cracks let in more water, speeding up the cycle.
Dealing with it
Keeping water OUT of the concrete is the best way to interrupt freeze/thaw cycling, and to keep salts from reaching the rebar. The best way to do that is with a breathable, penetrating water repellent (like the ones PROSOCO makes, natch, which is how I know about this subject).
Before spraying your driveway, sidewalk or patio with the sealer, the concrete must be clean, dry and in good repair. We make plenty of products for cleaning the concrete, but you’ll have to go to your local hardware store to find stuff to fix cracks if your driveway has some already.
Sealers won’t bridge cracks.
The best sealers will soak into the concrete, imparting water-repellency from within. One advantage of penetrating sealers is that they can’t be worn or abraded off, so you get a service life of years. They are also breathable. That means they let moisture already in the concrete (there’s always some) evaporate out, but won’t let liquid water in.
These hundred-degree temps of late definitely have me thinking about the pleasures and beauties of winter. Snow days off from work, snow shoeing with the dogs, no bugs, no poison ivy — but winter can also do a number on your horizontal concrete. Now’s the time to take care of that little job, especially if your area is prone to early snow fall.