De-Icing Salt Damage: Protecting Interlock, Concrete and Plants
To protect interlock, concrete and plants from de-icing salt this winter, shovel first and salt sparingly. Plain rock salt (sodium chloride) is the least damaging choice for concrete pavers, and you should avoid magnesium chloride and CMA. Never salt concrete in its first year, and keep salty snow off garden beds and lawns. Most winter damage on London properties comes from using too much salt, not from the choice of product.
Every spring we see the same results of winter: white crust on interlock, flaking concrete steps, brown evergreens along the driveway, and dead strips of lawn beside the sidewalk. Mid-October, before the first freeze, is the time to plan how you'll handle ice. Here is what the industry and public agencies recommend, and how to apply it to a typical London property.
How de-icers damage hardscape
Salt doesn't usually "eat" good concrete directly. The damage comes from what salt does to water:
More freeze-thaw cycles. Salt melts ice, the meltwater soaks into concrete or joints, then refreezes overnight. Southwestern Ontario gets many of these cycles each winter.
Pressure inside the surface. Water expands as it freezes. On weak, porous or uncured concrete, that pressure pops off the top layer (scaling).
Chemical attack from some products. Certain de-icers react with the cement paste itself.
Which de-icer is safest for interlock and concrete?
The Concrete Masonry & Hardscapes Association (CMHA, formerly ICPI) is the industry body for interlocking pavers. Its paver FAQ says:
Rock salt (sodium chloride) is the least damaging to concrete materials and should be used whenever possible.
Calcium chloride can be used judiciously when you need faster melting in colder temperatures.
Magnesium chloride and CMA (calcium magnesium acetate) are not recommended, because they can chemically degrade all types of concrete.
Two more rules from concrete industry guidance:
Never use ammonium sulfate or ammonium nitrate (often found in fertilizers) as a de-icer.
No de-icers on new concrete. The Pennsylvania Aggregates and Concrete Association advises against using de-icers on concrete in its first year. If you poured a new walkway or pad this summer, use sand for traction this winter.
De-icer comparison
Rock salt (sodium chloride): Hardscape impact: Least damaging to concrete per CMHA; Notes: Becomes much less effective below about -10°C
Calcium chloride: Hardscape impact: Use judiciously; Notes: Works in colder temperatures; easy to overuse
Magnesium chloride: Hardscape impact: Not recommended by CMHA; Notes: Can chemically degrade concrete
CMA (calcium magnesium acetate): Hardscape impact: Not recommended by CMHA; Notes: Marketed as "eco," but hard on concrete
Sand or grit: Hardscape impact: No chemical effect; Notes: Traction only; sweep up in spring
Interlock-specific tips
Good-quality concrete pavers are dense and absorb little water, which is why they hold up to salt better than many poured surfaces. Problems usually show up at the joints and the base:
Check the joint sand before winter. Missing joint sand lets water into the base, where freeze-thaw can heave pavers.
Polymeric sand needs to be cured. Alliance Gator, a polymeric sand maker, says properly cured polymeric sand won't be harmed by de-icing salt. It must be installed above 0°C, so late-season repairs need a warm, dry day.
Keep a slope. CMHA recommends a slope of about 2% or more so meltwater runs off instead of sitting.
Use plastic shovel edges or a rubber-edged blade to avoid chipping paver edges.
Clean up in spring. Sweep up leftover salt and sand once the ice is gone.
If your interlock is already settling or heaving, the problem is likely the base, not the salt. Our post on interlock base prep that survives freeze-thaw explains what goes underneath.
Protecting plants and lawns
Salt hurts plants in two ways, according to Virginia Tech Extension:
Salt in the soil pulls water away from roots. Plants look drought-stressed even when the soil is moist.
Salt spray from plows and passing traffic burns buds and needles directly.
Signs of salt damage include browned leaf tips and margins, dead buds, early fall colour and branch dieback, usually on the side facing the driveway or road.
To reduce damage:
Don't pile salty snow on beds or lawns. Choose a snow storage spot that drains away from plants.
Wrap or screen sensitive shrubs near the street with burlap.
Water deeply in spring to flush salt below the root zone.
Add organic matter such as compost or mulch to beds near driveways.
Choose salt-tolerant plants for roadside beds. Extension lists include red maple, river birch, winterberry, summersweet and arrowwood viburnum.
Lawn edges along driveways often need repair in spring. Fresh topsoil and sod usually do the job. See our sod installation page.
How much salt is enough?
Most homeowners use far more than needed. Some Ontario guidance:
Shovel first, then salt. Peel Region's Less Salty campaign reminds residents that salt only melts ice above about -10°C, so shovel or scrape first and salt only where needed.
About a tablespoon per square metre is a common target after shovelling, according to advice reported by CBC London.
Sweep up and reuse leftover salt crystals.
Pre-treat when possible. Salting before a storm stops ice from bonding to the surface and usually needs less product.
Spring cleanup after a salty winter
Once the snow is gone, a little cleanup prevents lasting damage. Sweep leftover salt and grit off interlock, concrete and decks, and rinse surfaces with water. Check paver joints and top up sand where it has washed out. Look for flaking on concrete steps and walks, and note it for repair. Rake salt-damaged lawn edges, add fresh topsoil, and reseed or re-sod. Give shrubs near the driveway a deep watering to flush salt below the roots.
Why it matters locally
Road salt doesn't disappear when the snow melts. Environment and Climate Change Canada's assessment found road salts pose a risk to plants, animals and aquatic environments. Parts of the Upper Thames near urban areas already have chloride levels close to federal guidelines, according to researchers quoted by CBC London. Every bag you don't use helps the Thames River.
Commercial properties: Smart About Salt
For businesses, condos and plazas, salt use is a liability issue as well as a maintenance cost. The Smart About Salt program, which started in Waterloo Region over drinking water concerns, certifies contractors in salt management. Our post on commercial snow and ice and the 60-day notice rule covers the legal side.
Pre-winter hardscape checklist
☐ Top up joint sand on interlock (polymeric sand only above 0°C)
☐ Note any low spots where water pools on patios and walks
☐ Choose a snow storage spot away from beds and lawns
☐ Buy rock salt and sand; skip magnesium chloride and CMA
☐ Mark any concrete poured this year as "no salt"
☐ Wrap sensitive shrubs near the street
☐ Get plastic or rubber-edged shovels
FAQ
What is the best ice melt for interlocking pavers?
The Concrete Masonry & Hardscapes Association says rock salt (sodium chloride) is the least damaging to concrete pavers. Calcium chloride can be used judiciously. Magnesium chloride and CMA are not recommended.
Can I salt new concrete?
Concrete industry guidance says not to use de-icers on concrete during its first year. Use sand for traction on new concrete this winter.
Does salt damage polymeric sand?
Alliance Gator, a polymeric sand manufacturer, says properly cured polymeric sand won't be harmed by de-icing salt. It must be installed above 0°C to cure properly.
How do I protect shrubs from road salt?
Don't pile salty snow on beds, wrap sensitive shrubs near the road with burlap, water deeply in spring to flush salt, and choose salt-tolerant plants for roadside areas.
Does rock salt work in extreme cold?
Rock salt becomes much less effective below about -10°C. Shovel first, then use sand for traction or a small amount of calcium chloride in very cold weather.
Keep your hardscape in shape
SPM Landscape & Excavation has built and repaired interlock, walkways and landscapes across London since 2006. We are WSIB covered and carry $1 million in liability insurance. Whether you need joint sand topped up, low spots fixed or salt-damaged lawn edges re-sodded, call (519) 474-0008 or email spmlandscape@gmail.com.
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