Interlock driveway snow removal in Durham Region, and the three millimetres that decide it

The driveway moves because it is built 150 to 200 millimetres deep and the frost in this region is specified at 1.2 metres. That gap is the honest answer and it is not a criticism of anybody's workmanship. The hardscape specifications call for a granular base of at least 150 mm for a residential driveway on well drained soil and 150 to 200 mm as the working range. The City of Toronto construction specification for concrete unit pavers, which governs this pavement on public right of way and has no reason to be generous, sets its minimum at 200 mm for a driveway. Nobody anywhere publishes a base depth that reaches frost, because reaching frost on a driveway would cost more than the house it serves.

What frost actually is here has been measured locally and it is on the public record. Two geotechnical investigations by the same consulting firm, filed with the City of Pickering as planning documents, one for a site on Brock Road in December 2019 and one for a site on Granite Court in March 2023, both state that foundations exposed to weathering should have at least 1.2 m of earth cover for protection against frost action. Both classify the native material as having high frost susceptibility. One of them describes the local silty clay in exactly those words and the other says the same of the sandy silt till.

Why clay rather than sand is the thing that matters was settled by the National Research Council of Canada in 1962 and has not been overturned since. Coarse sands and clean gravels do not heave. Fine sand and silts are very susceptible. Clays also are very susceptible, although they normally heave slowly, and because their pores are smaller they develop higher heaving pressures than silt does. The mechanism is not the water already in the soil expanding as it freezes. It is water drawn upward from unfrozen soil below to the freezing plane, where it forms a lens of ice that lifts everything above it.

Which brings it home. The soil survey of Ontario County, the federal survey covering Pickering, Ajax, Whitby and Oshawa, maps Darlington loam on clay loam till over 20,700 acres, Whitby loam as the imperfectly drained counterpart of it, and Schomberg clay loam on lacustrine clay. The survey of Durham County, covering Courtice, Bowmanville and the rest of Clarington, maps Newcastle clay loam across the old glacial Lake Iroquois plain and describes that plain as extending over a portion of the three southern townships. The ground under most driveways in this service area is clay or clay loam over till, which is the exact material the National Research Council names as very susceptible, sitting under an assembly that stops 1 metre short of the frost.

Then the freeze thaw count does the rest. The Great Lakes Integrated Sciences and Assessments consortium publishes a regional average of about 42 freeze thaw cycles a year for the Great Lakes region, with a maximum of 60 and a minimum of 23.4, counting the times the temperature crosses freezing and dividing by two. That figure is regional and it is not an Oshawa reading, which is worth saying plainly rather than borrowing the precision. Even at the low end it is a lot of lifting and settling for one winter, and every cycle is an opportunity for a joint to lose sand and for a unit to come back down a fraction higher than it started.

So the realistic goal is not a driveway that does not move. It is a driveway whose joints stay full, whose edge restraint still holds, and whose high units get found in October rather than in January by a blade. The hardscape guidance agrees: where heave is caused by frost it recommends frost resistant subbase material, and where faulting has happened it says the blocks may be reset, with the base repaired first if the base is the cause.

Work diagonally to the joints, and the reason is geometry rather than preference. The published winter maintenance instruction for this pavement is to shovel and plough on a diagonal so that the tool never runs along a joint line, and the warning attached to it is that lippage worked at square angles chips paver edges. Picture a course that has lifted across the width of the driveway. A blade running straight up and down the driveway meets that whole raised line at once, every unit in it simultaneously. A blade crossing at an angle meets one corner, then the next, then the next, and each contact is a fraction of the load.

The second instruction is about the shoes, the skids that set how high the cutting edge rides. The guidance is to adjust worn shoes so the blade rides at a height that removes as much snow as possible without catching paver edges. On asphalt a shoe is a convenience. On interlock it is the control that decides whether the edge touches stone at all, and a shoe that has worn down over a season quietly lowers the blade onto the surface it was set to clear.

The third is the one almost nobody publishes, and it answers a question Durham homeowners ask every April. Worn steel shoes can embed metal filings from the shoe into the paver surface, and that is where the rust coloured staining comes from. It is not the salt, it is not the stone bleeding, it is powdered steel sitting in the pores of a concrete surface and oxidizing in the spring rain. Synthetic shoes are available which prevent exactly that, and the same guidance recommends considering plastic snow shovels or synthetic blade edges on this surface.

A homeowner with a shovel inherits all three rules. Cross the joints at an angle, keep the blade from digging, and a plastic shovel beats a steel one on this one surface even though steel is better on everything else. A homeowner with a snow blower inherits a fourth, which is that the skid shoes on the blower do the same job as the shoes on a plough blade and are set the same way: high enough that the auger housing never touches stone.

Our own practice on an interlock property is to agree the direction of travel at the pre season walk around and write it in the file, because the direction that works on a given driveway depends on where the courses run and where the snow has somewhere to go. A driveway laid in a herringbone pattern already presents its joints at an angle to the length of the driveway, and the diagonal that is right on a running bond is not automatically right there.

The Canadian product standard for concrete pavers already contains a de icing salt test, and that is the single most useful fact on this page. CSA A231.2 specifies requirements for concrete pavers made from hydraulic cement concrete for pedestrian and vehicular traffic areas, and it carries a compressive strength test at clause 7.2 and a de icing salts freeze thaw durability test at clause 7.3. The standard itself sits behind a paywall, so the numbers below come from two independent public specifications that cite it and agree with each other exactly.

The City of Toronto construction specification for concrete unit pavers, TS 3.80, dated September 2025, requires a minimum average compressive strength of 50 MPa on laboratory cured specimens and, for freeze thaw durability tested immersed in a three per cent salt solution, no greater mass loss than 225 grams per square metre after 28 cycles or 500 grams per square metre after 49 cycles. McGill University master specification 32 14 15, citing CSA A231.1 and A231.2, publishes the same three figures, plus a maximum absorption of five per cent that only that one document gives.

Read what that test actually is. Forty nine complete freeze thaw cycles, with the unit sitting in salt water the whole time, and a pass requires losing less than half a kilogram of material per square metre of surface. No Durham driveway is treated that hard. The honest conclusion is that the common worry, that salting an interlock driveway will eat the stone, is answered by the product before anybody picks up a spreader, provided the pavers were sold to the Canadian standard.

The published advice on which de icer is less honest than the test is, and this is worth saying rather than smoothing over. The hardscape association names rock salt as the least damaging to concrete materials, suggests judicious use of calcium chloride, and recommends against magnesium chloride and calcium magnesium acetate on the grounds that they can chemically degrade all types of concrete. The cement industry position is similar, putting sodium chloride and calcium chloride in the acceptable column for good quality dense concrete. But a Utah Department of Transportation report from June 2014, which is a transport agency rather than a trade body, says the opposite about rock salt, that sodium chloride causes scaling of concrete surfaces and increases the rate of corrosion of embedded steel.

Underneath the disagreement sits a sentence from the peer reviewed literature that explains why it exists. Valenza and Scherer published a two part critical review of salt scaling in Cement and Concrete Research in 2007 and concluded that although salt scaling is a major durability issue for concrete, there is no agreement regarding the cause of the damage, and consequently no means for preventing it can be identified. That is why the Canadian standard tests an outcome, grams lost per square metre, rather than a mechanism. Anybody who tells you confidently which chemical reaction is damaging your driveway is ahead of the published science.

Where all three positions do agree is the absolute. Never use a de icer containing ammonium sulphate or ammonium nitrate, because those are too aggressive and will destroy a concrete surface. Those compounds turn up in fertilizer, and the bag of fertilizer in the garage is the thing a homeowner reaches for when the salt runs out in February. It is the one de icing decision on this page that has no grey area in it.

An interlock driveway is held together by the sand in the joints, and the published trigger for topping it up is a drop of more than twelve millimetres. The pavement works because load on one unit is transferred to its neighbours through the sand filled joint, which is where the word interlock comes from. Empty the joints and the units stop sharing load and start working as individual blocks, which is when edges chip and courses go out of line. The maintenance guidance is to inspect the joints, and where the sand has dropped more than half an inch, top up the joint sand immediately.

Here is the part that surprises people, and it is published guidance rather than a trade opinion. Top up with dry masonry sand, because using polymeric sand for topping up joints is not recommended. Polymeric sand, the kind that sets hard when it is wetted, is a product for a full installation, where the joint is filled from the bottom and the whole surface is treated at once. Dropped into a partly full joint as a repair it bridges the top and leaves a void underneath, and the next freeze finds that void.

The association is equally clear that joint sand stabilizers do not add structural capacity, so the base design must not count on them. That is a useful sentence to carry into a conversation with anybody who proposes sealing or stabilizing a driveway as a cure for movement. It is not a cure for movement. It is a way of keeping sand in a joint that already works.

The practical Durham sequence is to top up joints in late October when the surface is dry and before the ground closes, not in April when the damage has already happened. Water flow, wind, aggressive cleaning and tire action are the four things that empty a joint, and three of those four are at their worst in a winter with a lot of melt. A driveway that sheds meltwater down one edge will lose that edge first, every year, and that is the edge to look at.

That chalky white film on the pavers at the end of winter is almost certainly efflorescence, it is harmless, and winter is the season that produces it. The Portland Cement Association describes efflorescence as a crystalline deposit, usually white, formed when calcium hydroxide left over from cement hydration reaches the surface and reacts with carbon dioxide in the air to form calcium carbonate. Three conditions have to coexist: soluble compounds in the material, moisture to carry them, and evaporation or pressure to move the solution. Remove any one and it does not happen.

The winter link is chemical rather than coincidental. Efflorescence is more common in winter because the slower rate of evaporation allows the salts to migrate to the surface, and because calcium hydroxide dissolves more readily in cold water. The masonry association adds the spring half of the cycle: moisture that froze inside the material thaws, dissolves more salts and pushes them outward, which is why it often looks worse in March than it did in January.

The useful part for a homeowner is that it is described as generally harmless and it often disappears by itself. On pavers specifically the published note is that it does not affect structural performance or durability, that it can appear within months of installation, and that it frequently peaks within about sixty days of the pavement first getting properly wet. Scrubbing it with an aggressive cleaner in March is a good way to open the surface and lose joint sand at the same time, for a problem that was going to resolve on its own.

There is one case where white on a paver is worth a second look, and that is when it appears only in a band along the edge where a salt pile sat, rather than across the field of the driveway. That pattern is a concentration problem rather than a cement chemistry problem, and the answer to it is the application rate in the previous section.

If the walk around finds a course sitting more than three millimetres high, the right purchase this autumn is a paver reset, and it is not a purchase we sell. We do not do hardscaping, we do not reset pavers, and we do not relay a base. That position is published on our own add on page: hardscaping sits on the referred out list here, alongside sod, grading, irrigation repair and any tree work above ladder height. Buying a winter of plowing for a driveway that needs a reset first is buying the thing that will find the defect rather than the thing that fixes it.

Second, and this one costs us a sale every year. If you qualify for your municipality's snow clearing assistance program, join it. Whitby charges nothing at all for its windrow and sidewalk service and its applications close on November 1. Clarington runs its enrolment from September 21 to October 31 and charges $107.69 including HST for the season. Pickering runs an income tested fee that is zero for residents receiving the Guaranteed Income Supplement. No contractor beats free, and no contractor should try to talk you out of it.

Third, be clear about what the entry membership does on a driveway. Silver, the $129 a month plus HST entry tier, leaves the driveway to you and carries no morning target at all. What Silver covers is the 5 PM windrow pass after a storm, plus four full clears a season banked against a request, and salting forms no part of it at any point in the winter. If your reason for calling is a cleared interlock driveway before you leave for work, the tier that does that is Gold, and quoting you the entry price against that promise would be the most common piece of dishonesty in this trade.

Fourth, if your driveway is a short single width with good drainage and you are physically able, a plastic shovel used diagonally across the joints is a perfectly good answer for an interlock driveway and we will say so. The arithmetic on hand clearing, including what a winter actually weighs, is set out on snow shovelling in Oshawa.

Three things this page would be stronger for having, and none of them could be opened. The first is CSA A231.2 itself. The standard is paywalled, so the strength, absorption and freeze thaw figures above come from two public specifications that cite it, the City of Toronto TS 3.80 of September 2025 and the McGill University master specification, which agree exactly on 50 MPa and on the 225 and 500 grams per square metre limits. The five per cent absorption figure rests on the McGill document alone. We also found no published CSA thickness class scheme, so the 60 mm and 80 mm figures in the drawing are hardscape association application guidance rather than a Canadian standard classification.

The second is a base depth published specifically for a paver driveway on a clay subgrade. It does not appear to exist. The guidance says only that in colder climates continually wet or weak soils will require thicker bases, and recommends drain pipes in clay soils subject to vehicular traffic. Anybody quoting you a clay specific number is quoting their own practice, which may well be sound, but it is not a published specification.

The third is a freeze thaw cycle count for Oshawa. The peer reviewed paper that would settle it, on freeze thaw cycles in Toronto in a changing climate, has its table of observed averages behind a paywall. The Environment and Climate Change Canada climate normals pages could not be read by the tools used for this research, which is a tool failure rather than a finding about the data. The regional figure quoted above is the Great Lakes average and it is labelled as such on purpose.

And one more, named because it is the kind of thing that gets assumed. No peer reviewed study of differential frost heave of segmental pavement on a clay subgrade could be found in the open literature. The closest permitted evidence is a cold climate test facility study in New Hampshire, funded by the hardscape foundation, which reported that winter plowing and freeze thaw did not dislodge any of the pavers, and that study is permeable pavement in a different state with no heave measurements in it. The argument on this page about why interlock moves in Durham rests on the frost depth filings, the soil survey and the National Research Council heave mechanism, which is three sources and not one, but it is not a direct measurement of a Durham driveway.

This was written by Andrew, who owns Northline Property Care and runs it out of Oshawa with six winters of Durham snow work behind him. The person who measures your property is the person who clears it, and the name on the invoice is the one answering the phone. The business carries full insurance and a CVOR registration, which is what Ontario requires of a work truck, and it carries no trade licence because the province issues none for this work.

This page was written against published documents rather than trade habit. Every figure in it carries the specification, by law, survey or journal it came from, and every external link goes to a standards body, a municipality, a federal agency, a university or a peer reviewed journal. Not one goes to another lawn care, snow removal or hardscaping company, which is a rule here rather than an accident, and it is the reason the page contains numbers that competitor pages do not.

Where the published record disagrees with itself, as it does on rock salt and concrete, the disagreement is printed rather than resolved in our favour. Where a figure could not be verified it is in the section that says so.