How the two differ in kind
Both go into the joints between pavers, both arrive in bags, and they are designed for opposite purposes.
POLYMERIC SAND is graded jointing sand with a binder that activates when watered and cures to lock the joints together. It resists the washout that opens joints and lets pavers wander, it suppresses weeds germinating in the joint, and it discourages ants and other insects from excavating it. Once cured it is substantially IMPERMEABLE — which on a conventional pavement, where water is meant to run off the surface to a drain, is exactly right.
OPEN-GRADED JOINT FILL is a small, angular, washed stone with the fines deliberately removed, and its job is the opposite: to stay open. On a permeable pavement the joints are the infiltration path, and although they are a small percentage of the surface area, essentially ALL the water enters through them. That water then passes into an open-graded bedding layer and a base that is designed as a storage reservoir, from which it infiltrates into the subgrade or discharges slowly through an underdrain.
So the joint material is not a finishing detail on a permeable pavement; it is the hydraulic inlet of the entire system. Filling those joints with polymeric sand does not reduce infiltration somewhat — it stops it. The pavement becomes impermeable, the reservoir beneath has no way to fill, and the water that the design assumed would soak away now runs off to wherever the surface falls, which is a place nobody designed for. Where the permeable construction was a planning condition or part of a drainage strategy, it is a compliance failure as well as a functional one.
The failure is also easy to arrive at innocently. A contractor asked to tidy a permeable drive, or a homeowner dealing with weeds in the joints, reaches for the product that solves the visible problem.
The factors that actually differ
Show
| Polymeric sand | Open-graded joint fill | |
|---|---|---|
| What it does | Sets to lock the joints, resisting washout, weeds and insects. | Stays open, so water can enter the pavement through the joints. |
| Permeability | Essentially none once cured. That is the point of it. | High, and it is the entire infiltration path of the pavement. |
| Where it belongs | Conventional pavements that shed water from the surface to a drain. | Permeable pavements, where the base is a storage reservoir. |
| What happens if swapped | On a permeable pavement it stops infiltration entirely, and the runoff goes somewhere undesigned. | On a conventional pavement it washes out of the joints, and the pavers lose their interlock. |
| Material | Graded sand with a polymer binder activated by water. | Small angular washed stone with the fines removed — fines are what would block it. |
| Installation sensitivity | High. It must go in dry, be swept clean off the paver faces, and be watered exactly as instructed — too little and it does not cure, too much and the binder washes out. | Lower. Swept in and compacted, topped up as it settles. |
| Haze on the pavers | The classic defect — binder residue left on the surface cures there and is very hard to remove. | Not applicable. |
| Weeds | Suppressed, which is the benefit most people buy it for. | Possible, and managed by maintenance rather than by sealing the joint. |
| Maintenance | Re-application where it has cracked out, and it does eventually. | Periodic vacuum sweeping to remove accumulated fines, which is what keeps the pavement permeable. |
| Consequence of neglect | Open joints, washout, and pavers losing interlock. | The joints clog with silt and the pavement loses its permeability — the slow version of the same failure. |
Which one, and when
Choose polymeric sand when…
- A conventional paved surface that sheds water to a drain or a gully.
- Joints that keep washing out — a drive on a slope, or an area that is pressure washed.
- Weeds and insects in the joints are the problem being solved.
- The pavement is not part of any drainage or infiltration strategy.
Choose open-graded joint fill when…
- The pavement is permeable, in which case there is no choice to make.
- The base was built as an open-graded reservoir, which only works if water can reach it.
- The permeable construction was required as a drainage condition or to offset impermeable area.
- Maintaining or repairing an existing permeable pavement — match what is there.
Now run your own numbers
This page holds no prices on purpose — a national average is wrong for almost every real project. Quantify both options with your dimensions and your local quotes.
Frequently asked questions
- What actually goes wrong if polymeric sand is used on a permeable pavement?
- The pavement stops being permeable, and everything downstream of that assumption fails with it. Nearly all the water entering a permeable pavement does so through its joints; sealing them leaves an impermeable surface over a base that was built as a storage reservoir and can no longer be filled. The rain that the design expected to infiltrate now runs off the surface to wherever it falls — frequently toward a building, since the pavement was never graded to drain anywhere, having not needed to. Where the permeable construction was a planning condition, or was counted in a drainage strategy as offsetting impermeable area, it is also a compliance failure. And it is not simply reversible: cured polymeric sand has to be removed from every joint, which is a slow mechanical job across the whole area.
- Why does permeable joint fill have no fines?
- Because fines are exactly what blocks the flow. The joint's permeability comes from the connected void space between angular stone particles, and adding fine material fills those voids — which is why the aggregate is specified as open-graded and washed, with the small fraction deliberately removed rather than merely low. The same principle runs through the whole build-up: the bedding layer and the base are open-graded too, so the water has a continuous path of connected voids from the surface down to the subgrade. It is also why the pavement's main maintenance requirement is periodic vacuum sweeping: fines accumulate in the joints over time from the atmosphere, from vehicles, from adjacent soil and from organic debris, and a permeable pavement that is never swept slowly clogs and loses the permeability it was built for.
- How is polymeric sand installed correctly?
- Dry, swept in, cleaned off, then watered exactly as the manufacturer states — and each of those steps causes a failure when it is skipped. The joints and the pavers must be dry, because the binder activates on contact with water and a damp surface starts curing it prematurely. The sand is swept in and compacted so the joints are full to the specified depth, then the paver faces are swept and blown completely clean, because any residue left on the surface cures there as a haze that is extremely difficult to remove. Then it is watered in the sequence and quantity the instructions specify: too little and the binder does not cure through the depth of the joint, too much and it washes the binder out of the joint and onto the surface. It also has a temperature and weather window — rain during curing ruins it.
- How do I tell whether my pavement is permeable?
- By the joints and by the base, and the joints are visible. A permeable pavement has noticeably wider joints than a conventional one — often with spacer nibs moulded into the paver to guarantee them — filled with small angular stone rather than sand, and the surface typically has no falls to a gully because it does not need them. The base is the confirmation: permeable construction sits on open-graded stone rather than a compacted sub-base with fines, and there is frequently an underdrain. Pouring a bucket of water onto the surface settles it in seconds — on a permeable pavement it disappears into the joints rather than running across the surface. If in doubt, the drainage strategy or planning documents for the property will say, since permeable paving is usually installed to satisfy a requirement rather than by preference.
- Can weeds be controlled in permeable joints?
- Yes, and not by sealing the joint, which is the response that causes the damage. Weeds in a permeable pavement germinate in the organic material and fines that accumulate at the top of the joints, so the effective control is the same maintenance that keeps the pavement working: periodic vacuum sweeping, which removes the seed bed along with the silt. Where there is heavy leaf fall or adjacent planting, sweeping more often addresses both problems at once. Spot treatment of weeds is possible with care, and hand removal works on a small area. What matters is recognising that a weedy permeable pavement is telling you it needs sweeping, and that the maintenance it is asking for is the maintenance it needed anyway to stay permeable.
- Does polymeric sand last?
- For years, and not indefinitely, and it fails progressively rather than all at once. Over time the cured joint can crack, particularly where there is movement, at edges, and where pavers are loaded by vehicles, and pieces work out leaving open joints. Freeze-thaw accelerates it. Pressure washing removes it readily, which is worth knowing before cleaning a drive that was jointed with it. Re-application into the affected joints is the remedy, and it needs the old material removed from those joints first so the new sand can fill the depth rather than bridging over a partly filled one. The related failure is applying it to joints that were not deep enough or not full: a thin layer of polymeric sand over ordinary sand does not lock anything and breaks up in the first season.
- What about the base under each?
- They are different constructions and the joint material has to match what is beneath it. A conventional pavement sits on a compacted sub-base containing fines, designed to be dense and stable, over which a bedding sand layer is screeded; water is shed from the surface. A permeable pavement sits on open-graded stone — a bedding course, a base, and often a deeper sub-base acting as a reservoir — all with the fines removed so water passes through and is stored in the voids, usually over a geotextile and sometimes with an underdrain. Putting permeable joint fill into a pavement over a conventional base achieves nothing, because the water has nowhere to go once it passes the joint; it simply sits at the top of the base. The joint, the bedding and the base are one system.
- How much material will the joints take?
- More than most people expect, because the joints are deeper than they look and the material settles. Quantity depends on the paver's thickness, since the joint runs the full depth, on the joint width, and on the number of joints per unit area, which is driven by the paver size — small pavers have far more joint length per square metre than large ones. Permeable pavers compound this by having deliberately wide joints, so their consumption is much higher than a conventional pavement of the same area. Both materials also settle after the first watering or the first rain and need topping up, which is a normal part of the installation rather than a defect. Ordering on a calculated joint volume with an allowance for settlement avoids the common outcome of running out part way across a drive with no matching batch available.