It’s one of those tips that gets passed around constantly on social media and gardening forums. Sprinkle salt on the weeds growing between your block paving, and they’ll shrivel up and die within a few days.
Simple, cheap, no chemicals needed.
So does salt actually kill weeds in block paving? Yes, it does.
But whether you should use it is a different question entirely. As landscaping experts, the GGM Landscaping team is here to guide you on better ways to prevent weeds in your block paving.
How Salt Kills Weeds in Block Paving – By Paving Experts
Salt kills plants through a process called osmotic dehydration.
When you apply salt directly to a weed or into the joint where it’s growing, the high concentration of sodium chloride draws moisture out of the plant’s cells. The weed can’t absorb water fast enough to replace what it’s losing, so it dehydrates, wilts, and dies.
On small, shallow-rooted weeds like annual grasses and young dandelion seedlings, this process happens within three to five days.
It works, and there’s no denying that it’s satisfying to watch a weed shrivel up after a pinch of salt.
The problem lies in what happens to everything else the salt touches and what happens after the weed is gone.
What Salt Does to Your Block Paving
Block paving relies on a precise structure to stay level and stable.
The blocks themselves sit on a compacted sand bed, and the joints between them are filled with kiln-dried sand or polymeric jointing compound. This jointing material is what locks the blocks together, prevents movement, and stops water from undermining the base layer.
When salt dissolves in rainwater and seeps into those joints, it breaks down the binding properties of the sand and gradually washes it away.
Over time, the blocks start to shift, rock, and settle unevenly, and once the joints are compromised, more water gets in and the damage accelerates.
Then there’s efflorescence.
This is the white, chalky residue that appears on the surface of paving when dissolved salts are drawn upward through the material and left behind as the moisture evaporates.
A bit of efflorescence happens naturally on new block paving and fades on its own. But repeatedly adding salt to the joints introduces far more sodium than the paving would normally encounter.
The white staining that results can be stubborn to remove and makes the paving look worse than the weeds did in the first place.
Freeze-Thaw Damage
This is the risk that most online guides either skim over or miss entirely. Salt is hygroscopic, which means it attracts and holds moisture.
When salt residue sits in or around your block paving, it pulls water into the porous surface of the blocks. That’s not a problem in summer, but in a Scottish winter, that trapped moisture freezes.
Water expands by roughly nine percent when it turns to ice, and when that expansion happens inside the pores of a concrete block, it cracks the surface from within.
One frost probably won’t cause visible damage, but repeated freeze-thaw cycles over a winter will gradually spall and pit the faces of the blocks.
The Impact on Surrounding Plants and Soil
Salt doesn’t just ruin your paving. Because it dissolves in the rain, it can travel into surrounding soil.
If your block paving runs alongside a lawn, flower bed, or hedge, the salt runoff can damage or kill plants well beyond the area you were treating. Grass along the edges of a salted driveway often yellows and dies back in patches, and it’s not always obvious that salt was the cause because the damage can take weeks to show.
What’s more concerning from a long-term perspective is what salt does to the soil structure itself.
Sodium breaks down the aggregates in soil that allow air and water to move through it, leaving you with compacted, poorly draining ground where very little wants to grow.
So When Is Salt Acceptable?
We wouldn’t recommend salt as a routine weed treatment for block paving, but we’re not going to pretend it’s never appropriate either.
If you have a small, isolated patch of weeds in paving that’s well away from any planting, and you just need a quick fix before guests arrive or for a one-off tidy-up, a small amount of table salt applied directly into the joints on a dry day will kill the visible growth.
Just make sure to use it sparingly, don’t apply it before rain is forecast, and accept that there is a chance you will need to re-sand the joints afterwards.
Better Methods to Get Rid of Weeds in Block Paving
Manual Removal
It’s not glamorous, but pulling weeds by hand or using a block paving knife is still one of the most effective methods.
The key is getting the whole root, because weeds like dandelions and creeping buttercup will regrow from any fragment left behind. If you do some weeding after the rain, the soil in the joints is soft so the roots should come out more easily.
Run a stiff wire brush along the joints afterwards to clear any remaining growth and loosens debris that seeds could settle into.
Boiling Water for Weed Killer
Pouring boiling water directly onto weeds kills them on contact by destroying the cell structure. It’s free, it’s chemical-free, and it won’t damage your paving or joints.
The downside is that it only kills what’s above the surface, so deep-rooted weeds will always grow back. It is best to use this method on young, shallow-rooted weeds that haven’t had time to establish themselves.
White Vinegar
Household white vinegar is another popular option. It burns the foliage on contact and is effective on small, annual weeds.
Apply it directly to the weed on a dry, sunny day using a spray bottle to avoid it splashing on other plants. Like boiling water, it’s a contact treatment that won’t kill established root systems, so be expected to reapply.
It’s safe for most block paving. Although you should always test it on a spare block first if you’ve got lighter-coloured or natural stone paving, as the acid can occasionally cause discolouration.
Targeted Herbicide on Driveways
For established weeds with deep root systems, using herbicide as a spot treatment is an effective option.
Herbicide is absorbed through the leaves and carries down into the roots, killing the entire plant rather than just the visible growth.
It’s worth noting that herbicides has been the subject of ongoing debate around its environmental impact, so use it as a targeted last resort, never as a first choice. Always follow the label instructions on dilution and application.
At GGM Landscaping, we are committed to safe environmental practices. We always recommend ongoing weed maintenance and preventative care to stop problems before they start.
Prevention: The Approach That Actually Saves Time
Every method we’ve mentioned so far is reactive to remove weeds from your paving. The far better approach, and the one we recommend to every client, is to stop weeds establishing in the first place.
Sweep to Prevent Weeds Growing
Most weeds in block paving don’t grow up from underneath. They grow from seeds that blow into the joints and germinate in the debris that collects there.
Regular sweeping, even just once a fortnight with a stiff broom, removes the organic matter that weeds need to take root. It takes only five minutes and prevents hours of weeding later in the year.
Maintain the Condition of Your Joints
Beyond sweeping, the condition of your joints is what makes the biggest difference.
Joints that are full of compacted kiln-dried sand or polymeric jointing compound leave no space for seeds to settle. Polymeric sand is particularly effective because it hardens when wet, creating a semi-rigid joint that resists weed growth, insect intrusion, and washout from heavy rain.
If your joints have eroded or been washed out over the years, re-sanding them is one of the best things you can do for your paving.
Applying a block paving sealant after cleaning and re-sanding adds another layer of protection.
A good sealant fills the surface pores of the blocks, making them less hospitable to moss and algae, and it binds the jointing sand in place so it doesn’t wash out as quickly.
Sealed paving is also much easier to clean, because dirt and staining can’t penetrate the surface as deeply.
Alternatively, consider block paving vs. tarmac for a long term solution to weed control.
When to Call a Professional
If weeds have been growing unchecked for a long time, or if the joints have deteriorated to the point where the blocks are moving and the surface is uneven, a simple clean and weed probably isn’t going to cut it.
At that stage, the paving may need lifting, the base re-compacting, and the blocks re-laying with fresh jointing material.
It sounds like a big job.
But it’s still far cheaper than ripping everything out and starting again, and it’ll give you a surface that looks and performs like new.
If your block paving has seen better days and you want honest advice on whether it needs a clean, a repair, or a replacement, the GGM Landscaping team are here to guide you through your options with our paving ideas.
We will conduct a free, no-obligations survey of your driveway or patio to give you honest guidance on how it can be improved.
Give our friendly team a call today on 07946 322717 and we will help it get sorted.