Can you put new polymeric sand over old?

Putting new polymeric sand over old rarely lasts. A thin skin of new sand on old, hardened sand has nothing solid to bind into, so it cracks and peels out of the joints. The fix that holds on GTA interlock is clearing the old joints out deep enough and refilling them like a new install, on a dry day above freezing.

That’s annoying when the joints have only dropped a bit, there’s half a bag of polymeric sand in the garage, and sweeping it over the top looks like a twenty-minute job. It’s still the part worth getting right.

If you’d rather hand it off, clearing and re-sanding joints is part of our polymeric sand and weed removal service.

Why can’t you put new polymeric sand over old?

A thin top layer has nothing to lock into. Polymeric sand is made to fill and bind the whole joint, and it doesn’t bond to a hard layer of old sand underneath.

Alliance Gator’s blog answers this exact question. Adding a thin layer on top of what’s there is “not ideal”, it says, because the original sand can be old, dirty or of unknown condition. Its advice is to remove at least 1 inch and follow the steps for a new install.

Its FAQ is blunter about a close cousin of the same habit: filling the lower part of a joint with regular sand and putting polymeric sand on top. Alliance Gator calls that “topping” and says it’s very bad to do. The joint surface peels and flakes off, and any warranty is void.

The reason, according to Alliance Gator, is that without a firm, densely packed joint underneath, water and ice work their way in and the material on top fails. It recommends filling the entire joint depth with its sand, and Sika’s data sheet says the same for its product.

Are your joints actually too low?

Check before you buy anything. Alliance Gator wants polymeric sand to finish at least 1/8 inch below the chamfer (the bevelled top edge of the paver), and 3/16 or even 1/4 inch below on wider joints. Joints sitting at that level are probably where they should be.

If they’ve dropped further, the sliver you’d add is far thinner than the 1.5-inch minimum joint depth Alliance Gator and Techniseal give for their sands. It won’t stay put through foot traffic, tires and a GTA winter.

How deep do you need to remove the old sand?

At least 1 inch, and 1.5 inches (about 38 mm) on most products. The manufacturers don’t all say it the same way:

So the safe target is 1.5 inches unless your bag says otherwise. You don’t always have to dig every joint down to the base, though.

Alliance Gator’s blog says some old polymeric material may stay put under the pressure washer, and that in most cases it’s fine to leave it and fill the washed-out areas with new sand. Sika is stricter. Its sheet says to remove all the existing sand, to the full depth or at least 38 mm.

How do you get the old polymeric sand out?

A pressure washer does most of it. Alliance Gator’s blog calls a pressure washer the best way to remove existing jointing material and recommends a 25-degree tip on a machine of at least 3,000 psi. Packed, weedy joints may need a scraper or joint tool first to break up the crust.

The catch is the bedding sand under the pavers. Alliance Gator’s G2 instructions for an existing paver surface warn not to disturb it while you clear the joints.

Let it dry completely

Then comes the slow part. The pavers, the joints and the sand below all have to be completely dry before new sand goes in.

All three manufacturers above call for a dry surface, and Techniseal and Alliance Gator explain why: moisture activates the binder early, so it sticks to the paver surface and stains it. Alliance Gator adds that damp joints stop the sand sliding down and packing tight.

To check, push a small screwdriver into a few joints. If the sand comes up dark or clumps, wait.

Can you patch just a few joints?

Yes, if the damage is local and you treat each patched joint like a new one. Alliance Gator’s advice for moss-damaged joints is to pressure wash out the damaged sand where it comes out readily, let the area dry, then replace the missing sand and activate it per its directions.

Fill those joints the same way as a new install, down to where the washer stopped, rather than skimming the surface.

If most of the surface has bad joints, it’s usually less work in the end to clear and re-sand the whole area in one go. Our polymeric sand guide lists the signs that point to a full replacement.

When can you re-sand interlock in the GTA?

Late spring through September is the reliable window around Markham and the rest of the GTA. The sand needs dry pavers and above-freezing temperatures while it cures, and the shoulder seasons are cold at night more often than people expect.

Environment Canada’s 1981–2010 climate normals for the Buttonville station in Markham show it clearly:

Re-sanding also takes longer than a fresh install because of the pressure washing. The pavers and joints have to dry out completely before the sand goes down. Then the new joints need their own dry stretch afterwards (48 hours above 0°C for Techniseal RG+).

In October that’s often hard to line up. Products with a 5°C minimum, like Sika’s, rule out more of spring and fall than the 0°C sands do.

What are the common mistakes when re-sanding?

Most failed re-sanding jobs come down to a short list:

1. Sweeping new sand over joints that were cleared only half an inch or so.
2. Putting sand down on pavers or joints that are still damp after pressure washing, so the binder sticks to the paver faces and stains them.
3. Blasting out the bedding sand, so pavers sink or rock afterwards.
4. Re-sanding over a section that’s already sinking. Fix the pavers first; our guide on why interlock sinks explains how.
5. Skipping the plate compactor. Alliance Gator says 30–50% of the sand drops on the first pass, and joints left loose let water in and fail.
6. Leaving dust on the paver faces before watering. Our guide to removing polymeric sand haze covers the cleanup if that happens.
7. Starting in late October and getting a frost before the joints have dried.

The refill itself (sweeping, compacting, blowing off, showering in sections) works the same as on a new install. Our step-by-step polymeric sand guide walks through it.

When is it worth calling someone?

A small patio with loose, crumbling joints is a reasonable weekend job if you have patience for the drying. It gets harder when the joints are packed hard with old polymeric sand, the area is a full driveway, or some pavers have sunk.

Then the pressure washing turns into a long day, and the risk of washing out the bedding goes up.

We do this work across Markham and nearby, including Richmond Hill and Stouffville: clearing the old joints, fixing any low spots, then re-sanding. You can see what that looks like in our interlock restoration project, or read more on our polymeric sand service page.

For a free quote, call (437) 684-2535 or text us a photo of your joints.