Some joints empty because the sand has simply aged out. Others empty in the same place every year, in a line, and that is water telling you where it runs. The second kind does not need more sand, it needs the run changed, and that is the difference between a repair and a subscription.
Sand that has aged out goes everywhere at once and goes slowly. Sand that washes out goes in a path: a line of joints running from where water arrives to where it leaves, often a course or two wide and usually deeper at one end.
Once you see that shape you have the diagnosis, and it is nearly always one of three things. A downspout putting a roof's worth of water onto one spot. A grade sending lawn or garden runoff across the paving rather than around it.
Or a perimeter that has lost its edge restraint, so the field has crept outward and the joints at that edge are now wide enough to move sand through.
Refilling the line without changing any of those is a repair with a known expiry date, which is why we trace it first and quote the drainage work as its own line rather than folding it in.
A line of empty joints is a channel and a general emptying is age. Which one you have decides whether this is sand work or drainage work.
Find where it enters
Downspouts, garden grades and open perimeters are the three usual sources, and finding the right one is most of the diagnosis.
Change the run first
Grading, a channel drain or new edge restraint, quoted on its own line so you can see what the drainage is costing against the paving.
Then refill the joints
New polymeric sand goes in last, once there is a reason to expect it to stay where it is put.
Under The Surface
A washed joint means a washed base
Sand does not leave a joint on its own; it is carried, and whatever carried it went down through the base as well. So a run of empty joints is usually sitting above a strip of base that has lost its fines and is now closer to loose gravel.
That is why a washout line often becomes a settled line a year or two later. Opening a test spot tells us whether you are still in sand territory.
Because water runs along that line. Sand does not leave on its own, it is carried, and until the run changes the new sand goes the same way as the old.
Very often. A roof delivers a large volume to one small spot, and that spot is where the joints empty first and the base washes out next.
We can, and it will hold about as long as the last lot. If the shape says channel rather than age, the honest answer is to change the run first.
Usually to some degree, since whatever carried the sand went down through the base as well. A test spot tells us whether it is still only a sand job.
It varies from a few hundred for a downspout extension and a re-grade to a few thousand for a channel drain, and it is quoted separately so you can see it.
The joints stay full through a wet spring. That is the test, and it takes one season rather than one week. If sand is low again by May the source was not the one we changed, and we come back and look again.
