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By Taylor Teasdale, Owner ·
The weeds in a block paving driveway are not coming up from underneath. That surprises people, and it changes everything about how you deal with them.
Underneath a properly built driveway is a compacted stone sub-base — no soil, no light, nothing can root through it. What weeds actually grow in is the gap between the blocks, where years of dust, grit, moss and leaf litter have packed down into something close enough to soil for a seed to take.
So the question is not how to kill the weeds. It is what is in your joints.
Why they come back every year
Most people attack the growth, clear the visible weeds, and feel they have fixed it. The joint is still full of the material the next seed will root in, so by the following spring it is back, and often thicker.
Worse, the most common way people clear it — a pressure washer on a narrow nozzle — empties the joint of its sand. An empty joint is deeper, collects debris faster and holds more moisture than a filled one. That is why a driveway often looks spectacular for a fortnight after a wash and worse than ever by the next year.
What actually works, in order
1. Kill it and let it die back. Treat the growth and give it a week or two. Pulling living weeds breaks the stem and leaves the root; killing first means the whole thing lifts out.
2. Get it out of the joint. The aim is to remove the material the seeds rooted in, not to drive it further down. A joint rake or a stiff blade along the joints does this well.
3. Clean the surface sensibly. A rotary flat-surface cleaner, or a wide fan held well back and kept moving. Never a narrow nozzle close in — that cuts into the block face as well as emptying the joints.
4. Let it dry, then refill every joint. This is the step that decides whether any of the rest was worth doing. Kiln-dried sand swept in and vibrated down, or polymeric compound if you want it to last. The surface must be properly dry or nothing goes in.
5. Seal it, if it is worth it. On a shaded, north-facing or tree-covered driveway, a breathable sealer locks the sand in and slows everything down for years.
Kiln-dried sand or polymeric?
Kiln-dried sand is cheap, easy and what the driveway was originally built with. It also washes out gradually, especially on a slope or under a downpipe, so you are topping it up every couple of years.
Polymeric compound sets firm, holds through heavy rain and keeps joints closed for years. It costs more and it needs laying properly — dry joints, correct misting, no residue left on the block faces — but on a driveway you are tired of fighting, it is the one to choose.
What not to do
Salt, bleach or strong vinegar. They kill the plant and then run off into the border, the lawn and the water table. Salt in particular damages the ground either side and can affect the concrete itself.
A weed burner near a resin driveway. Fine on concrete and block, genuinely damaging on resin-bound.
Washing without re-sanding. Worth repeating because it is the most common mistake of all. If you only do one thing differently after reading this, make it that.
If the joints keep emptying
Joints that will not stay filled usually mean something else is going on — a failed edge restraint letting the blocks spread, or water running across the driveway in a channel rather than draining away. In that case the weeds are a symptom and the fix is elsewhere. Worth having someone look properly before you re-sand it for the third time.
Want it done once, properly?
We clean, kill off the growth, refill every joint and seal it if you want. A day's work and you stop fighting it every spring.
Common questions
Weed and jointing questions
They are not growing up from the soil underneath. Dust, grit, leaf litter and moss build up in the joints over the years, and that is the soil — seeds blow in and root in it. Which is why the answer is about what is in the joint rather than what is under the driveway.
Used properly, yes. Used badly it is the single biggest cause of the problem. A narrow nozzle held close blasts the jointing sand out, and an empty joint collects dirt faster and holds more seed than a filled one. Use a wide fan or a rotary flat-surface cleaner, keep it moving, and always re-sand afterwards. Washing without re-sanding leaves the driveway worse than before.
A kiln-dried sand with a binder mixed in. You sweep it into dry joints, mist it with water, and it sets firm. It resists washing out, stays put through heavy rain and keeps weeds out for years rather than months. It costs more than plain sand and it is usually worth it, particularly on a driveway that slopes or sits under trees.
It helps considerably rather than being a magic answer. A sealer locks the jointing sand in place and makes the surface less hospitable to anything trying to root, so the growth that does appear sits on top and brushes off. On a shaded or north-facing driveway it is the difference between doing this every couple of years and every five.
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