Problem & Solution Page

Ant Hills Between Your Interlock Pavers? Why They're There and How to Stop Them Coming Back

By Riaad, Owner & Project Manager · ICPI Certified Installer · Last updated July 15, 2026

Little sand volcanoes pushing up between your stones, joints emptying out, maybe a paver that rocks when you step on it. The ants are not the problem. They are the receipt for a joint that already failed, and no amount of spray will change that.

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What This Page Covers

  • Why ant hills between pavers are a symptom of failed joint sand, not a pest issue
  • How to tell whether you need a re-sand, or whether the damage has gone structural
  • The real fix ladder, what a cheap fix costs you in two summers, and honest DIY limits

What That Sand Mound Actually Means

Ants cannot dig through a properly compacted, correctly sanded joint. That is the whole diagnosis in one sentence, and it is the thing five pest-control companies will not tell you in July.

A paver joint that was built right is a 3 to 5 mm gap filled the full depth of the stone with sand that has been vibrated in, watered, and cured into a firm plug. A pavement ant, the species behind essentially every sand mound we see, probing that joint finds nothing to excavate and moves on to somebody else's driveway. When you see a mound, it means those ants found loose, dry, gritty material they could carry out grain by grain, and the pile on the surface is the spoil from a tunnel that already exists below.

So the mound is a measurement. It tells you roughly how much sand has left the joint, and it usually tells you the sand has been leaving for a while. By the time a colony is established enough to throw visible mounds in mid-July, that joint has typically been open since the spring melt at minimum, and on Hamilton clay lots more often since the winter before that.

This is why the spray-and-wait cycle never ends. You are killing the tenant and leaving the apartment furnished and unlocked.

Interlock paver driveway installation at a residential brick homeInterlock paver patio with dining set in a townhome backyard

Why Your Joints Emptied Out, Ranked by How Often We See It

Across the driveways and patios we look at in Hamilton, Ancaster, Dundas, Burlington and Oakville, the causes stack up in roughly this order.

  • 1. The original install used regular sand, not polymeric. This is the big one, and it is most of the older stock in the region. Plain masonry or concrete sand has no binder. It is loose aggregate sitting in a slot. Water flushes it, wind lifts it, and ants relocate it. A driveway sanded with regular sand in 2012 has effectively been shedding joint material for fourteen winters.
  • 2. Cheap sweep-in or "contractor grade" bagged sand. The stuff that promises you a weekend fix for $12 a bag. Some of it has a token binder, most of it does not, and almost none of it holds up to a Hamilton freeze-thaw season. It looks fixed in August and is gone by June.
  • 3. Polymeric sand installed wrong. The product is good. The install often is not. Poured into a joint that was only cleaned out 10 mm deep, never compacted with a plate before watering, over-watered so the binder washed to the surface, or under-watered so it never cured. Worst of all, hit by a thunderstorm ninety minutes after placement. We wrote up the timing risk in detail in polymeric sand cure time and rain risk in Ontario, because it is the single most common way a good product produces a bad result.
  • 4. Water moving across the surface faster than it should. A downspout dumping onto the field, a patio with no fall, or a driveway apron collecting the whole roof's runoff. Look at where your ant hills are. If they cluster in a strip below a downspout or along one edge, that is not coincidence, that is a hydraulic problem eating a joint. That one needs the water addressed or the sand goes again.
  • 5. Failed or missing edge restraint. If the perimeter spikes have rusted out or the plastic restraint was never pinned properly, the field spreads a few millimetres every season. Joints widen, sand falls through, ants follow. This is common on driveway edges that meet a soft lawn shoulder.
  • 6. Sealer applied over a joint that was already empty. Sealing does not fill a joint. It just glazes the void shut on top while the tunnel keeps running underneath.

Notice what is not on that list: an ant problem in your yard. Ants are everywhere in southern Ontario. The homes that get ant hills between the pavers are the ones with joints that let them in.

The Screwdriver Test: Diagnose It Yourself in Ten Minutes

Do this on a dry day, and do it in at least six spots spread across the whole surface, not just where the mounds are.

  • Step 1 — Probe the joint. Take a flat-blade screwdriver and push it straight down into a joint. On a healthy polymeric joint you will get maybe 3 to 6 mm of give and then firm resistance you cannot beat with hand pressure. If the blade slides down 25 mm or more with no resistance, that joint is a void. Anywhere the blade goes past the halfway point of the paver's thickness, the ants have a highway.
  • Step 2 — Measure the drop. Look at the top of the sand relative to the top of the paver. Joint sand should sit within about 3 mm of the paver surface, right at the bottom of the chamfer. If you are looking down 10 or 15 mm into a dark slot, you have lost most of the plug.
  • Step 3 — Rock test. Stand on each paver near a mound and shift your weight corner to corner. A stone that is solid is a joint problem. A stone that ticks, rocks, or drops a millimetre under your heel is a bedding problem. Write down how many rock.
  • Step 4 — Sight the plane. Crouch at one end and look across the surface at eye level, or lay a 6-foot level or a straight 2x4 across it. Look for dips, waves, or one paver sitting proud of its neighbour. Anything over about 6 mm of deviation under the straightedge is telling you the base has moved, not just the sand.
  • Step 5 — Count the field. Roughly what percentage of the surface has mounds or open joints? Under 25 percent and localised is one conversation. Over 25 percent or scattered everywhere is another.

Now read your results:

  • Deep joints, nothing rocks, plane is flat. This is the good outcome, and it is most of the calls we get. It is purely a joint failure. Clean and re-sand and you are done for years.
  • Deep joints and a few stones rock, plane still flat. Borderline. Usually fixable with a proper joint rebuild plus resetting the handful of loose stones on fresh bedding sand.
  • Deep joints, multiple stones rock, visible dips or lippage. The ants are now the least of your problems. Go read uneven interlock and patio sinking, because you are looking at a base issue and re-sanding it will waste your money. We are not going to re-explain base failure here; those pages cover it properly.
  • You re-sanded within the last year and the sand is already gone again. Something is either flushing it out with water or the base is pumping. Same answer as above, plus have a hard look at your downspouts and grading.

The Fix Ladder, In Order

Do these in sequence. Skipping a rung is how people end up doing this twice.

  • 1. Clear the joints properly. Not a broom. The old material has to come out to a minimum of 25 mm deep, and we usually target 30 to 40 mm on a driveway. That means a joint rake or a mechanical joint cleaner, and on badly contaminated surfaces a pressure wash with a controlled fan tip. The number one cause of a failed re-sand is a joint that was only cleaned 10 mm deep, because the new polymeric never gets thick enough to form a plug that holds.
  • 2. Verify what's under there before you refill. When the joints are open you can actually see the bedding course. If the bedding sand is contaminated with fines, wet, or dished out under the stones, sanding over top of it is decoration. This is the inspection step most homeowners skip, and it is the one that decides whether you are re-sanding or relaying.
  • 3. Check and reset the edge restraint. Walk the whole perimeter. Restraint should be continuous, pinned at roughly 300 mm centres into a compacted base, and sitting tight to the stone. If the field can spread, the joints will reopen no matter what you fill them with.
  • 4. Sort out the water. If a downspout is discharging onto the field, extend it. If a corner ponds, that is a grading conversation and you can start with our yard drainage page. Fixing joints under a downspout without moving the downspout is a two-year fix at best.
  • 5. Re-sand with polymeric, in lifts. Surface bone dry. Sand swept in, then vibrated with a plate compactor over a protective pad so it settles into the joint, then topped up and vibrated again. You are chasing full-depth fill, not a surface skim. Sweep the excess off carefully, because polymeric residue left on the face hazes the stone permanently. Then water it exactly to the manufacturer's spec.
  • 6. Watch the weather like it matters, because it does. Most polymeric products need a rain-free cure window, and a July thunderstorm rolling off the escarpment two hours after placement will wash the binder out and leave you a crusty mess. This is the part DIYers lose on most often.

Bait and spray sits nowhere on that ladder. If you want to knock the colony down while you wait for a booking, fine, it will buy you two or three weeks. Just be clear with yourself that you bought time, not a fix. The full maintenance picture is in our interlock maintenance guide for Ontario, and the specific costs for cleaning, sealing and re-sanding are broken down in interlock cleaning, sealing and re-sanding costs in Halton.

DIY or Call Someone? An Honest Answer

Plenty of this is genuinely DIY-able and we would rather tell you that than sell you something you do not need.

Do it yourself if: the affected area is small, under roughly 150 square feet, nothing rocks, the plane is flat, and you have a clear four-day dry stretch in the forecast. Rent a plate compactor for the day, buy a joint rake, budget $30 to $45 a bag for a real polymeric product, and read the bag's water instructions twice. A single-strip walkway or one patio corner is a good weekend job.

Call a contractor if: it is a driveway carrying vehicle loads, the area is large enough that you cannot get the sand in and the excess off before a rain window closes, stones are rocking, you can see dips, or you have already tried this once and it failed. Driveways are where the DIY math turns against you, because the consequences of an incomplete joint under a 2,000 kg vehicle compound fast, and because you cannot practically compact and cure 600 square feet of new joint sand before the weather turns.

Definitely call if the sand loss is recurring within one season. That is not a sand problem. Something below is moving, and every re-sand you buy is a payment on a debt you are not actually paying down.

The judgment call in the middle, and we will be straight that it is a judgment call, is the patio with deep joints and two or three rocking stones. Some of those we rebuild the joints and reset the loose stones and they hold for a decade. Some of those open back up in three years because the base was marginal and we were optimistic. It depends on what the bedding looks like once the joints are open, which is why we do not quote that one over the phone.

Interlock paver driveway with contrasting ribbon banding

What It Costs, and What the Cheap Version Costs You

A full clean and polymeric re-sand on a typical patio is priced per site, driven by access, paver age, joint depth and how much contamination has to come out. Material alone is $30 to $45 a bag depending on the line, and a bag covers roughly 65 to 100 square feet on a normal joint width, less if your joints are wide open. The detailed breakdown is on our cleaning, sealing and re-sanding cost page.

Compare that to the alternative. Pest control for a paver driveway is a few hundred dollars a visit and you are booking it every July, forever, because you are treating a symptom. Five years of that is real money spent on a problem that got worse the entire time.

And if you let it run to the structural end, you are into lift-and-relay, which means pulling the stones, rebuilding the base, and resetting the field. That is not a re-sand price. For context, a new interlock driveway installed all-in runs $28,000 to $48,000 and a patio $22,000 to $42,000. A relay is a fraction of that, but it is an order of magnitude above what you would have spent fixing the joints in year one. The re-sand is the cheapest hour on the clock. It is just the least dramatic-looking one, which is why it gets deferred.

Local Expertise (E-E-A-T)

  • Credentials: ICPI Certified Installer, Landscape Ontario member, Unilock and Techo-Bloc Authorized Installer. Installing and repairing interlock across Hamilton and Halton since 2013.
  • Riaad's Pro Tip: Before you buy a single bag of sand, probe six joints with a screwdriver and stand on every paver near a mound. If nothing rocks, re-sand and you are done. If things rock, stop and get eyes on the base first, because sand will not hold up a stone that has nothing under it.
  • Why mid-July: Peak colony activity lines up with the driest joints of the year. It is not that the ants arrived in July. It is that July is when you can finally see what the spring melt took out.

Frequently Asked Questions

Because the joint sand between those pavers is loose, dry or already partly washed out, and the ants found it. Ants cannot chew through a properly compacted, correctly sanded joint. They excavate loose material and push the spoil up onto the surface, which is the little sand volcano you are looking at. That mound is not the ants making a mess. It is the ants telling you how much sand has already left the joint, and often that the bedding layer underneath has started to move too. If you have ant hills, you have a joint problem first and a bug problem second.
Take away the habitat, not the ants. Permanent control means removing the failed joint sand to a depth of 25 to 40 mm, confirming the bedding sand and base underneath are still sound, refilling the joints with polymeric sand compacted in lifts, and checking that the edge restraint is still pinned. Ants will not colonise a joint they cannot excavate. Killing the colony while leaving the void open just means the next colony moves into the same address, usually inside two summers. On the Hamilton and Halton driveways we service, joints re-sanded properly stay ant-free for years, and the ones treated with spray alone come back.
Yes, when it is installed correctly, and that qualifier matters more than the product. Polymeric sand contains binders that fuse the grains into a firm, semi-flexible plug once it is watered and cured. Ants cannot tunnel through it and cannot carry the grains out individually. But polymeric sand that was poured into shallow joints, never compacted, or hit by rain before it cured turns into a crumbly crust that ants get under within one season. The product does not fail often. The installation does.
Both, but the living-in-it came first. Ants move into a joint that has already lost sand. Once they are established they accelerate the damage, because every tunnel they dig moves bedding sand up and out, which enlarges the void under the paver. On a driveway carrying vehicle loads that turns a cosmetic problem into a structural one faster than it would on a patio. The honest answer is that ants rarely cause a failure on their own, and they reliably make an existing one worse.
It works on the ants and does nothing to the driveway. Bait will knock down a colony, usually within two to three weeks, and you will get a quiet stretch. Then a new colony finds the same empty joints and you are back where you started. Pest control kills the tenant. It does not fill the vacancy. That is why the same paver driveways get sprayed every July for years without ever getting better. Spray is a reasonable short-term measure while you wait for a re-sand booking. It is not a fix.
Because the void is still there, and in Ontario the void gets a little bigger every winter. Freeze-thaw cycling from November through April works joint sand loose and lifts it, spring melt and heavy rain rinse the loosened grains out, and by mid-July the joints are dry, open and ideal nesting ground. That is the annual cycle you are stuck in. It repeats until somebody fills the joint with material the ants cannot excavate and water cannot flush out.
Not on their own, but they can absolutely make a paver rock, and rocking is how sinking starts. Ants relocate bedding sand from under the stone up to the surface. Lose enough of the bedding course and the paver loses its support at one corner, tips slightly under load, and starts grinding the joint wider every time it moves. On a clay lot in Hamilton or Ancaster where the base is already sensitive to moisture, that is how a joint problem turns into a settlement problem. If stones already rock underfoot or you can see a dip, you are past re-sanding and into a lift-and-relay conversation.
Spot re-sanding works only when the failure is genuinely local, such as one corner under a downspout or a single strip along a drip line. If ants are showing up in more than roughly a quarter of the field, re-sand the whole surface. Polymeric sand needs a continuous cured plug to resist water and excavation, and patching new sand against old, failing sand gives you a seam that fails first. Spot work also leaves an obvious colour difference. On most patios, a full clean and re-sand costs a small fraction of a lift-and-relay and outlasts three rounds of patching. We price it per site, because access, paver age and joint depth move the number more than square footage does.

If Your Problem Has Gone Past the Joints

This page is deliberately scoped to ants and joint integrity, because that is what most mid-July calls actually are. If your diagnostic said otherwise, these are the right pages:

Related Pages

If you want a straight answer on whether yours is a re-sand or something bigger, we will come look, probe the joints, and tell you which one it is. Sometimes that answer is "your joints are fine, buy a bag of bait, call us in five years." We would rather say that than sell you a driveway you do not need. Get a free quote or call +1 (289) 700-0312, Monday to Saturday, 7 AM to 7 PM.

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