Deicing Salts And Concrete
Deicing Salts and Concrete Checklist
- Rock other deicing salts will NOT harm strong concrete
- Salt attracts water
- Apply silane/siloxane sealers - CLICK HERE to BUY it
- Apply SAND to concrete
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Deicing Salts - Does It Really Harm Concrete?
DEAR TIM: We just moved into our new house. Our builder has advised us not to use rock salt on our concrete sidewalks and driveway for snow and ice removal.
He told us that it will damage the concrete. I don't believe him, because our city uses it on our streets every winter. Does my builder know what he is talking about? S. D.
DEAR S. D.: Your builder's advice is somewhat accurate. Rock salt can be one of concrete's worst enemies if the concrete was not mixed, finished and cured properly. Avoid using it on your concrete sidewalks, driveways, and patios if they have not been installed correctly.
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Is All Concrete Harmed By Deicing Salt?
No. Lots of old concrete was installed correctly and deicing salt does not harm it.
I grew up in the Midwest in Cincinnati, Ohio. Cincinnati can get brutal below-zero temperatures in the winter. I can take you to places in downtown Cincinnati that have concrete sidewalks that have been in use for fifty or more years and the top surface never spalled or was damaged by years of rock salt used to melt snow and ice.
How Strong Is the Old Concrete?
I've never had the opportunity to core drill one of these old concrete surfaces, but if we could I'm willing to bet you that the concrete would test out at least 5,000 pounds per square inch (PSI) of compressive strength. You just need to add an extra bag of Portland cement per cubic yard to get this strength or greater.
Watch this video by a top chemist who explains what salt can do to concrete. Pay CLOSE ATTENTION to what he says starting at 3:00 into the video. You'll note that he mentions if the concrete is mixed and placed properly, it can withstand the pressure from the freezing and thawing cycles.
Why is New Concrete Damaged By Salt?
I can also take you to new homes where concrete driveways and sidewalks look horrible after two years of winter weather because the concrete was not mixed, installed, finished or cured properly.
Concrete is a magnificent material. As a paving material, it can be one of the longest lasting surfaces that you can use. However, its useful life can be significantly reduced if you do not recognize its weaknesses.
How is Concrete Weak When Stretched?
Concrete has high strength when it is compressed, or 'squeezed'. However, it is extremely weak when it is subjected to tension, or 'pulled'. Rock salt can take advantage of this weakness.
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Does Concrete Absorb Water?
Believe it or not, while concrete appears to be a very dense material, it is in fact quite like a blotter. It can and does absorb water. You can actually see this happen on a hot summer day. Sprinkle some water on your sidewalk or driveway and look very closely. You can actually see the water penetrate the surface of the concrete.
When you spread rock salt on your concrete to melt snow and ice, the salt dissolves the snow and makes a salt water mush. The melting action of the salt allows water to enter the concrete. If the temperature then drops and the water freezes, the growing ice crystals can blast apart the concrete.
Does Salt Attract Water?
Salt is also hygroscopic. It attracts water. It can cause concrete to become more saturated with water than it would otherwise. The presence of this extra water in freezing conditions can spell trouble.
The volume of water increases by 9 percent when it freezes within the concrete matrix. The pressure of the growing ice crystals can cause the surface of the concrete to fail. It usually spalls off.
New Concrete = DANGER
Freshly poured concrete is most susceptible to damage. Concrete placed in the late fall needs at least 30 days of drying time. This young concrete is still highly saturated with water. The water within the concrete can freeze and cause the surface to pop off.
However, if enough cement was in the initial mixture and this cement was not diluted by the addition of water, the concrete will be able to resist the damaging forces of the freezing water.
What is the Best Concrete Strength Mix Recipe?
Always order concrete that will attain a minimum compressive strength of 4,000 pounds per square inch (PSI). Some parts of the USA call this a six-bag mix. In order to achieve a 4,000 PSI rating, a cubic yard of concrete would have six bags, or 564 pounds of Portland cement in it. A typical bag of Portland cement weights 94 pounds.
IMPORTANT TIP: Remember, this is a MINIMUM requirement. If you're pouring an outdoor slab, driveway, patio, sidewalk, etc. and you want it to look great for thirty, forty or fifty years, then order it with seven or eight bags of cement per cubic yard of concrete.
Portland cement is CHEAP. A bag of it retail at a big box store in 2017 only cost about $10.00. Ready-mix concrete plants pay much less than that for 94 pounds. In other words, would you pay $200 more for your concrete if you knew it would be extremely strong?
Should I Add Air To Concrete?
Be sure that is air entrained as well. These two things are a good defense against salt attack. Concrete which is ordered, placed, finished, and cured properly can resist decades of contact with rock salt. Concrete surface failures such as spalling can almost always be traced to workmanship errors.
Can Finishers Ruin The Concrete?
Yes, it's my belief that most concrete that is harmed by deicing salts happens because of workmanship errors.
The placement and finishing of the concrete is critical as well. The upper surface of concrete can be severely weakened by poor workmanship. Sometimes workers add water to concrete at the job site or use it as a finishing aid.
These practices dilute the amount of cement at the surface of the concrete. The cement is the ingredient in concrete that holds everything together. To resist the freeze/thaw action of water, you need to have strong concrete at or near the surface.
IMPORTANT TIP: This means water should NOT be added to the concrete at the job site. It means that the workers should NOT trowel in the bleed water that comes to the surface after the concrete has been bull floated.
Is Sand Best To Use on Snow and Ice?
There is an alternative to using rock salt. You can use sand. The sand will not melt the snow and ice, but it will provide you with traction.
Should I Seal Concrete With Siloxane?
Yes, you should seal your concrete in the early fall with a silane/siloxane clear penetrating sealer. You can also treat your concrete with clear coatings that minimize or eliminate the possibility of water being absorbed by your concrete. CLICK HERE to BUY a great silane siloxane water repellent.
These ingredients allow the clear coatings to breathe. Avoid using products that contain silicone or paraffin.
Should I BEWARE of Film Formers?
Some sealers can produce a surface film. A surface film may not allow the concrete to breathe.
I've walked on some film-forming sealers that are very slippery when wet. Only buy a sealer like the one above that SOAKS into the concrete.
Concrete soaks up water from the soil. This water passes through the concrete and eventually evaporates. However, if you trap this water at the surface with film forming sealants, you may cause spalling. Be careful!