Anyone who has laid a paved surface knows the problem. After a few weeks, weeds sprout from the joints and ants start building nests in the sand bed. The right joint filler keeps both under control for years.
Why joints matter
Filled joints transfer load between neighbouring stones and hold the bond together. They also let rainwater drain into the bedding layer. Without filler, the stones shift under load over time.
Leave joints empty or fill them with loose sand, and seeds settle in and insects move in.
The weed problem
Weeds in paving joints keep coming back. Even on a new surface, dandelion, grass or moss can take over the gaps within six months. Wind carries seeds into open joints, bird droppings contain undigested seeds, and fine humus builds up between the stones to form a nutrient layer.
In Germany, the Plant Protection Act bans herbicides on paved surfaces, and many other countries restrict them too. So the fix has to come from the joint material.
The ant problem
Ants like loose sand. They dig tunnels, carry material to the surface, and create voids underneath the stones over time. Stones sink, the surface becomes uneven, and water pools.
Ants in paving joints don’t mean the work was poor. Fine bedding sand is ideal building material for them. The remedy is a filler that is too hard or too coarse to nest in.
Three joint filler options compared
1. Quartz sand (simple and cheap)
Washed quartz sand (0–2 mm grain size) is the classic choice. It is swept dry into joints and compacts through rain and foot traffic.
Advantages:
- Very affordable
- Easy to apply
- Fully water-permeable
Disadvantages:
- No weed protection, seeds germinate directly in the sand
- No ant protection, ideal nesting material
- Needs periodic refilling after heavy rain
Best for: Secondary areas where occasional weeding is acceptable.
2. Polymeric sand (weed stop)
Polymeric sand contains binders activated by water. Once cured, it forms a flexible yet firm surface within the joint.
Advantages:
- Strongly inhibits weed growth (no loose germination layer)
- Significantly reduces ant nests
- Remains water-permeable
- Lasts 5–8 years
Disadvantages:
- More expensive than quartz sand
- Application window matters (no rain)
- Risk of haze on stone surfaces if applied incorrectly
Best for: Patios and paths where clean joints matter.
3. Epoxy resin jointing mortar (professional solution)
Two-component resin mortar cures completely and seals the joint for good. Weeds can’t root in it and ants can’t dig through it.
Advantages:
- Complete weed protection
- No ant nesting possible
- Extremely durable (10+ years)
- Colour stable
Disadvantages:
- Significantly more expensive
- More complex application (mixing, timing)
- No longer water-permeable, drainage must be handled by slope
- Difficult to repair
Best for: Driveways, high-profile patios, areas with heavy weed pressure.
Comparison table
| Property | Quartz sand | Polymeric sand | Epoxy mortar |
|---|---|---|---|
| Weed protection | ✗ | ✓✓ | ✓✓✓ |
| Ant protection | ✗ | ✓✓ | ✓✓✓ |
| Water permeability | ✓✓✓ | ✓✓ | ✗ |
| Approx. cost per m² | Low | Medium | High |
| Durability | 1–2 years | 5–8 years | 10+ years |
| Application difficulty | Low | Medium | High |
How much joint filler do I need?
The quantity depends on three things:
- Surface area in square metres
- Stone size (determines the number of joints per m²)
- Joint width and depth (determines joint volume)
The smaller the stones, the more joints per square metre and the more material you need. A 10×20 cm stone has twice the joint length per m² compared to a 20×20 cm stone.
PatioPlanner calculates the quantity for you. Once you set surface, stone and joint width, the shopping list shows the filler in kilograms and bags for each material.
Practical tips
- Joints must be dry and clean. Dust and moisture prevent bonding with polymeric sand and mortar.
- Fill joints to about 2/3 of the stone height, not flush with the top, so rainwater does not run over the joint.
- Sweep off excess material immediately. Dried polymeric sand on the stone surface is very hard to remove.
- Mind the temperature. Polymeric sand and mortar need at least 5 °C to cure properly.
Which one to pick
Against weeds and ants, use polymeric sand or resin mortar. Quartz sand is the budget option for secondary areas, but you will refill and weed it regularly.
PatioPlanner calculates the joint filler along with the sub-base and curbstones for your surface.