Why is the sand washing out of my paver joints?

The paver documents do not rank where joint sand goes first. What they do is tie particular places on a surface to particular causes, and that is how this page reads a driveway with low joints.

• Under an eave or at a downspout: Tech Spec 6 lists concentrated runoff flows among the causes of joint sand loss, and ICPI Tech Spec 5 gives gutters receiving sheet flow and the drip lines under the eaves of buildings as examples of concentrated water flow, naming downspouts and eaves again for residential surfaces.
• Along a slope: Tech Spec 6 lists steep slopes among the applications prone to joint sand loss.
• In an exposed, windy spot: Tech Spec 6 names driving winds as a cause and continually windy areas as prone to loss.
• In wide, irregular joints: ICPI says tumbled pavers and circular patterns have wider joints than other paver shapes.
• Across the whole surface after a wash: Tech Spec 6 names excessive cleaning, and separately pressure washing, among the causes.
• Where vehicles drive and park: Tech Spec 6 names saturated bedding sand that pumps under traffic loading, a cause that starts below the joint.

More than one of those can apply to the same surface, and none of them can be pinned on a driveway from a page. The list tells a homeowner what to look at, not which cause is at work.

Tech Spec 6 puts the stake in one line: "Joint sand loss/pumping typically includes removal of some or all joint sand, an essential component of interlock and pavement stiffness." The sand between the units is part of how the pavers hold each other in place, which is why the guide treats its loss as something to replenish rather than a cosmetic gap.

Cleaning is on that list, and ICPI's high pressure rinse guidance ties keeping sand in the joints to the spray a nozzle makes and the angle it meets the surface. How a cleaning can disturb the joints is answered in full under whether paver cleaning can damage the joints, and the order a cleaning follows, chemistry first and pressure last, under cleaning means chemistry before pressure.

One cause on Tech Spec 6's list is not about the top of the joint at all: saturated bedding sand that pumps under traffic loading. The guide groups it with joint sand loss under one heading, loss and pumping. Topping up is Tech Spec 6's step for the joints, while the bedding layer sits under the pavers, so pumping bedding sand, like a base that has moved, is for a paver installation contractor to assess.

For loss at the top of the joint, what a stabilizer is, whether ICPI treats it as optional, and the places the documents say it helps are set out under joint stabilization, and whether a sealer helps the sand stay is its own answer under whether sealing helps pavers hold their joint sand.

Concentrated runoff needs water, and Southwest Florida has a season of it. The National Weather Service's Tampa Bay Area office defines the rainy season for Southwest Florida as May 15 to October 15, with frequent showers and thunderstorms and a peak from July through early September.

What that rain means for paver joints in Naples, with NOAA's normals for the city, is set out on the service page under joint sand, weeds and the Naples rain.

Tech Spec 6 gives the trade's step. If the joint sand has dropped more than 1/2 inch, the guide says to top it up immediately, spreading dry masonry sand with a wide push broom so it falls into the joints and fills them to the bottom of the paver chamfers. It also says that using polymeric sand for topping up joints is not recommended.

Which sand goes in differs by document, and each line belongs to its publisher. Tech Spec 6 tops up with dry masonry sand. SEK-Surebond's site preparation bulletin fills joints with dry joint sand meeting ASTM C144. Seal 'n Lock, a Florida sealer maker, recommends a coarse fractured sand (C144) and says not to use mason or play sand because it is too fine. The paver maker and the product's label settle which sand a surface gets.

Low joints are not the same thing as low pavers. A spot where the pavers themselves have dropped is a different question, answered under whether sealing will fix sunken pavers.