What causes Vancouver jointing sand to wash out?

Jointing sand washes out in Metro Vancouver primarily because standard sand has no binding agent to resist the region's heavy, persistent rainfall — and Vancouver gets a lot of it.

Metro Vancouver receives over 1,200mm of rain annually, with North Shore communities exceeding 2,000mm, and roughly 70% of that falls between October and March. That's months of sustained rainfall hitting your paver joints repeatedly, and unbound sand simply cannot withstand that kind of hydraulic pressure. Each heavy rain event erodes a little more sand from the joints, and over one or two rainy seasons, joints that were once full become visibly empty — leaving pavers loose, unstable, and vulnerable to weed and moss intrusion.

The core problem is using the wrong sand in the first place. Standard mason sand, play sand, or even coarse construction sand are all unbound materials. They compact reasonably well when dry, but water moves through them freely and carries particles out of the joint with it. In a climate like Metro Vancouver's, this isn't a slow process — you can lose significant joint depth after just a few major rain events in November or December. Contractors who install with unbound sand in this region are setting their clients up for annual maintenance headaches.

Polymeric sand is the correct material for Metro Vancouver. It contains a blend of fine aggregate and a polymer binder (typically polyurethane or acrylic-based) that activates when water is applied during installation and then cures into a semi-rigid, flexible compound that resists washout. Quality brands — Techniseal, Alliance, and Sakrete are the most commonly used in the Lower Mainland — hold up significantly better than budget alternatives in sustained wet conditions. Even polymeric sand degrades over time in Vancouver's climate and typically needs replenishment every 3-5 years here, compared to 5-8 years in drier regions like the Interior.

Improper installation of polymeric sand is the other major cause of premature washout. Even the right product fails if it's applied incorrectly. The most common errors are:

• Insufficient joint depth before sanding — joints need to be at least 1 inch deep (25mm) for polymeric sand to have enough mass to resist erosion. If the bedding sand level is too high, the joint is too shallow and the polymeric sand layer is too thin to hold
• Improper activation — polymeric sand must be activated with a controlled, gentle water application (a fine mist, not a blast from a hose) to wet it thoroughly without washing it out of the joints. Over-watering during activation flushes the polymer binder out before it can cure
• Activating before rain — in Metro Vancouver, timing the activation is critical. If rain arrives within 24 hours of application before the sand has cured, it can wash out just like regular sand. Installers need to check the forecast carefully and allow a full dry cure window

Surface slope and drainage also play a role. If your paver surface doesn't have adequate slope — minimum 2% (about ¼ inch per foot) away from the house — water pools on the surface and sits in the joints rather than running off. Standing water in joints accelerates sand erosion and creates ideal conditions for moss and weed growth. If you're seeing sand washout concentrated in low spots or areas where water ponds, the underlying issue is drainage, not just the sand itself.

For maintenance, if your joints are visibly depleted, the fix is straightforward: sweep out any remaining loose sand and debris, clean the surface (a pressure washer at 1,500-2,000 PSI works well), let the pavers dry completely, apply fresh polymeric sand, sweep it into the joints, blow off the excess with a leaf blower, and activate with a gentle mist. This is a DIY-friendly task that most homeowners can handle on a dry weekend in late spring or early summer. In Metro Vancouver, plan to do this every 3-5 years as routine maintenance.

If you're planning a new installation or having existing work redone, Vancouver Interlock can match you with experienced local contractors who understand this climate — get matched for free through the Vancouver Construction Network.