Weeds grow between paving bricks because the joints have opened up and filled with wind-blown dust and organic debris — which is, from a seed’s point of view, a perfect narrow seedbed with guaranteed moisture underneath. The permanent fix is not a stronger poison. It is refilling and stabilising the joints so there is nowhere for a seed to germinate in the first place.
Everything else — hand weeding, boiling water, herbicide, vinegar — is symptom management. Useful symptom management, and we will go through what actually works and what will damage the garden around it, but it is not the fix.
Why the joints empty in the first place
Properly laid paving has fine dry sand swept into every joint and compacted in. That jointing sand does real structural work: it creates the interlock that lets each block share load with its neighbours. When it goes, you get weeds first and loose blocks later.
In Cape Town, it goes for four reasons:
- Pressure washing. By far the most common cause. A high-pressure lance blasts jointing sand straight out of the joints. The paving looks brilliant for a fortnight and then sprouts weeds along every line, because you have just excavated a network of clean seed beds.
- Winter run-off. Heavy rain sheeting across paving carries sand out of the joints, particularly on slopes and anywhere water concentrates instead of spreading.
- The south-easter. Wind lifts dry surface sand off the joints in summer and replaces it with dust and organic debris, which is far better growing medium than clean sand.
- Movement. If blocks are shifting — failing edge restraint, a weak base — the joints widen mechanically. Weeds along one specific line, rather than everywhere, usually means movement rather than a sand problem.
That last one matters for diagnosis. Weeds evenly across the whole area is a maintenance issue. Weeds concentrated in one band, alongside a dip or an open edge, is a structural issue and no amount of weeding will resolve it — see our paving installation and prep guide for what should be under there.
Step one: clear what is there
Whatever you do next works better on clean joints. Options, from most to least garden-friendly:
| Method | How well it works | Risk to the garden |
|---|---|---|
| Hand pulling with a joint knife | Very good if you get the root; slow | None |
| Boiling water | Good on seedlings and moss; needs repeating | None beyond scalding adjacent roots at bed edges |
| Weed burner / flame gun | Good on soft annual weeds; poor on deep tap roots | Fire risk in summer; can mark some pavers |
| Household vinegar | Burns off top growth only; regrows from root | Acidifies soil where it runs off; harms plants it touches |
| Glyphosate-type herbicide | Effective on established and rooted weeds | Real — drift and run-off kill plants, and it moves into beds |
| Salt | Works, sort of | Never do this. Salt persists in soil, kills adjacent plants and can attack concrete and mortar |
Two rules if you use herbicide at all: apply it with a small directed applicator or a shielded nozzle on a still day, never a broadcast spray, and never on a day when rain is forecast, because run-off from paving concentrates into whichever bed the water drains to. On a sloped Cape Town property, that can be the neighbour’s garden.
For most domestic paving, the honest recommendation is boiling water plus a joint knife. It is free, it is completely safe around planting, and repeated over a few weeks it genuinely wins.
Step two: refill the joints properly
This is the part that actually stops the problem returning, and it is the part most people skip.
- Wait for dry paving and dry sand. Damp sand bridges at the top of the joint and leaves a hollow underneath. It has to be genuinely dry to run down.
- Use fine, clean jointing sand — not building sand full of organic matter, which is itself a growing medium.
- Sweep it in from several directions with a stiff broom, working it down into the joints.
- Compact it. Run a plate compactor with a protective mat over the area, or at minimum tamp it. This settles the sand deep into the joint.
- Sweep in a second pass. The joints will have dropped. Almost everyone stops after one pass and ends up with joints two-thirds full.
- Top up again a few weeks later. Traffic and rain will settle it further.
Full joints do two things at once: they leave no space for wind-blown soil to accumulate, and they restore the interlock the paving needs structurally. It is the same job as the one that keeps the paving flat.
Polymeric jointing sand: worth it or not?
Polymeric sand contains a binder that sets when wetted, forming a semi-rigid joint that resists weeds, washing out and ant activity. It is genuinely effective and it is the closest thing to a long-term answer.
The honest trade-offs:
- It costs considerably more than plain sand.
- Installation is unforgiving — the paving surface must be completely dry and swept absolutely clean before wetting, or you get a permanent haze on the blocks.
- It needs a dry weather window to install and cure, which in Cape Town means avoiding the winter months.
- It is harder to lift and relay individual blocks later.
- It is not immortal. It degrades over years and needs redoing.
Our view: worth it on a feature patio, a pool surround or anywhere joints keep washing out on a slope. Not worth it on a large plain driveway where ordinary sand plus an annual top-up does the job for a fraction of the cost.
Sealing
A paving sealer applied over stabilised joints locks the sand down and makes the surface much less hospitable to seeds. It also deepens the colour, which people either like or do not. Published Cape Town figures put sealing at roughly R45–R85 per m² in premium materials, and it is a periodic job rather than a permanent one.
Two warnings. Do not seal damp paving — you trap moisture and can get a milky bloom. And do not seal as a way of avoiding fixing loose or sunken blocks; it does nothing structural.
Reducing the weed pressure around the paving
Weeds arrive as seed. Reducing the seed supply nearby makes a measurable difference:
- Mulch adjacent beds with 50–75mm of bark or gravel. Less bare soil means less blown soil landing in your joints and fewer weeds setting seed next to the paving.
- Keep a clean edge. A proper edge restraint or mowing strip between bed and paving stops grasses and creeping groundcovers migrating into the joints. Kikuyu will colonise a paving joint with real enthusiasm.
- Cut weeds before they seed. One season of letting weeds flower in a corner supplies the next three years.
- Fix ponding. Any low spot that holds water after rain will be the first place things grow. Ponding is usually a falls or drainage problem — there is more on that in our driveway drainage guide.
- Sweep regularly. Removing leaf litter and dust before it works into the joints is the cheapest prevention there is.
A realistic annual routine for Cape Town
| When | Do this |
|---|---|
| Early spring (Sept–Oct) | Clear winter weed growth and moss while it is soft; check for ponding you noticed in the rain |
| Late spring | Sweep clean, top up jointing sand while everything is dry, compact and re-sweep |
| Summer | Pull the occasional seedling; sweep after windy spells; seal if you are going to, in settled dry weather |
| Autumn (Mar–May) | Final joint top-up before the rains; clear leaves; check edge restraint is intact |
| Winter | Watch where water runs. Do not pressure wash. Note any new dips |
Published figures for Cape Town put DIY annual paving care at roughly R600–R1 200 for a typical home with 80–120m² of paving, and a professional annual service — clean, re-sand, treat moss, inspect — at roughly R2 500–R5 500. The full maintenance picture is in our paving maintenance guide.
About pressure washing
It deserves its own section because it is the most common self-inflicted cause of this problem. Pressure washing is not banned — it is the fastest way to remove moss, algae and ingrained grime, and after a wet Cape Town winter that can be exactly what a driveway needs. The rule is simply this: if you pressure wash, you re-sand afterwards. Every time, without exception. Use a wide fan nozzle, keep the lance at a sensible distance and angle, and treat the re-sanding as part of the same job rather than something you might get round to.
Half the “my paving is suddenly full of weeds” calls we get trace back to a thorough wash three months earlier with no re-sand.
When weeds mean something worse
Call someone if you see any of these, because the weeds are a symptom rather than the problem:
- Weeds concentrated along one line or one patch rather than spread evenly.
- Blocks that rock underfoot or that you can lift by hand.
- A visible dip, rut or wave in the surface.
- Joints that have widened noticeably, especially at an open edge.
- Sand washing out of the same spot repeatedly after every rain.
All of those point to base or edge-restraint failure. Re-sanding buys a few months; a lift-and-relay of the affected area fixes it.
Getting it sorted
Re-sanding, joint stabilising and localised relaying are straightforward work and they extend the life of paving considerably. If your joints are empty or the surface has started moving, take a look at our driveway paving services or get in touch and we will tell you whether it needs a maintenance visit or a repair.
Quick answers
What is the best way to permanently stop weeds between paving bricks?
Refill the joints. Clear the weeds, let everything dry, sweep in clean fine jointing sand, compact it and sweep in a second pass. On feature areas, polymeric jointing sand or a sealer over stabilised joints extends that considerably.
Does vinegar or salt kill weeds in paving?
Vinegar burns off top growth but the weed regrows from the root. Never use salt — it persists in the soil, kills nearby plants and can attack concrete and mortar. Boiling water and a joint knife are safer and more effective.
Why did weeds appear after I pressure washed my paving?
Pressure washing blasts the jointing sand out of the joints, leaving clean open seedbeds. Always re-sand and compact the joints after washing, and top up again a few weeks later once the sand has settled.