How to clean interlock without damaging it

Interlock cleaning needs less gear than most people expect: a broom, dish soap, a nylon brush and a pressure washer turned down to about 1,500 PSI. The damage usually comes from shortcuts. A narrow tip held close to the stone does it, and so does acid poured on to save scrubbing, or joints left empty after the wash.

This guide is for concrete interlock pavers laid on a sand bed. Natural stone, clay brick and wet-cast pavers can react differently to some cleaners (Techniseal’s rust remover, for one, isn’t meant for any of them), so check the label for your material.

If you’d rather hand the whole job over, that’s what our interlock cleaning service covers. The numbered steps are further down the page.

What do you need for interlock cleaning?

For a light clean you need very little:

• A push broom and a nylon scrub brush
• A bucket of dish soap and water
• A garden hose
• A plastic scraper for anything stuck on

For a full clean, add a pressure washer with a wide fan tip (or a surface cleaner attachment), a leaf blower, rubber gloves and safety glasses. You’ll also want enough polymeric sand to refill the joints afterwards.

How much pressure is safe for pavers?

About 1,500 PSI, which is less than most machines can give. That figure comes from Western Interlock, a paver manufacturer in Oregon. If your washer isn’t adjustable, it says to hold the wand at least 24 inches from the surface and use the widest tip you have.

Unilock’s spring maintenance advice is similar: a low setting with a fan tip, the wand at about knee height, and the spray angled at 45 degrees so it doesn’t dig the sand out of the joints.

Keep the wand moving at an even speed and the same distance from the stone. Western Interlock notes that moving too fast leaves small swirl marks. Unilock warns that the wrong pressure or nozzle can crack or erode the paver surface.

The tip matters as much as the pressure. Here’s how Alkota, a pressure washer maker, describes the standard tips, and what that means on pavers:

Which cleaner works on which stain?

Treat the stains first, then clean the whole surface. Otherwise you end up with a patchy finish.

Use products labelled for concrete pavers, and test each one on a small hidden spot before you do the whole area.

Rust remover can leave its own mark. Techniseal says pavers can look spotted afterwards (it calls this a “clean stain”) and suggests cleaning the whole surface for an even result. It also warns that rust streaks from metal snowplough blades may never fully come out.

White powder is a different story. Unilock notes that efflorescence removers are usually acid-based and can shift the colour slightly. Efflorescence is also usually temporary and fades on its own, so on newer pavers it can pay to wait.

If the white film appeared after new joint sand went in, it may be polymeric sand haze instead, which needs a different fix. Our guide on removing polymeric sand haze explains how to tell them apart.

Why does washing take the sand out of the joints?

Because water under pressure moves loose sand, especially when it’s aimed into the joints. Unilock warns that the wrong pressure or nozzle can blow joint sand out, and the last step in its cleaning routine is to check the joints and sweep in new joint material.

On an older driveway the joints are often half empty or full of weeds anyway. So a full clean usually ends with new polymeric sand.

That step has its own rules:

1. The joints must be dry to the bottom, not just the paver faces.
2. The surface has to be blown spotless before any water touches it.
3. The weather has to cooperate. Techniseal’s instructions for its RG+ sand say to plan for 24 hours without rain and to keep temperatures above 0°C through a drying period of at least 48 hours.

Check the bag you buy, too. Techniseal recommends its HP2 formula rather than RG+ for joint replacement on an existing installation. Our polymeric sand guide covers how deep to clear the joints and how much sand you’ll need.

When is the best time to clean interlock in Ontario?

Any time from spring to early fall works, ideally on a mild, overcast, calm day.

Spring makes sense in the GTA. Melting snow, ice and spring rain wash salt, grit and dirt onto the pavers, and the joints can need attention after a winter of freeze and thaw.

A few Ontario-specific points:

• Leave yourself room for the re-sanding step. If frost is likely in the next two days, wait, because the new joint sand needs temperatures above 0°C for at least 48 hours while it dries.
• Avoid the hottest part of a summer day. Techniseal says not to apply its stain remover under blazing sun and never to let it dry on the surface.
• Early fall is a good second window, as long as the nights are still above freezing. Freshly set joints go into winter full, with less room for water and weeds.
• In winter, go easy on de-icers. Unilock says rock salt can be used on driveways, but sparingly, and that magnesium-based products should be avoided. Rock salt stops working below about -9°C anyway.
• Unilock suggests a plastic shovel too, because metal blades can scratch pavers and leave tiny metal bits that turn into rust streaks.

Mistakes that damage interlock

Most cleaning damage comes down to one of these:

• Using a red 0° tip or a turbo nozzle up close. It can erode the face of the paver, and you can’t wash that out.
• Spraying straight down into the joints, which blows the sand out of them.
• Scrubbing with a wire brush, which can leave rust spots behind.
• Reaching for muriatic acid or mixing products to make them stronger. Techniseal points out that its paver rust remover contains no muriatic acid so it won’t damage the material, and says not to mix its cleaners with other chemicals.
• Letting a cleaner dry on hot pavers before rinsing.
• Sealing a surface that isn’t fully clean. Techniseal’s guidance is that sealing dirty pavers never gives the intended result, and efflorescence sealed in stays trapped under the film.
• Walking away with the joints empty. Open joints collect dirt and weed seeds, and pavers with nothing between them to hold them tight can start to shift.

If you’re thinking about sealing after the clean, read our interlock sealing guide first. It’s optional, and timing matters more than the product.

When is it worth calling someone?

A small patio or a single walkway is a fair weekend job if you’re patient and test before you spray.

It’s worth getting help when:

• the area is a large driveway
• moss and weeds are in nearly every joint
• stains haven’t moved after a proper try
• you’d rather not rent equipment and handle the polymeric sand step yourself

If some pavers have sunk or rock underfoot, cleaning won’t fix that. Those sections need lifting and relaying first.

We do interlock cleaning and pressure washing across Markham and nearby towns like Richmond Hill and Stouffville, along with weed removal and joint-sand replacement. Call (437) 684-2535 or text us a photo of the area, and we’ll come and look and give you a free quote.

Decks and fences need gentler settings again. Our guide on pressure washing decks, fences and interlock covers those.