Salt as a residual herbicide

[Grumps]

I have block paving (clay-based I think) and having cleared all the weeds in the gaps want to add something that will inhibit weeds returning. I understand salt will work but am a bit anxious in case the salt might damage the blocks. Is this really a danger?

[Bob_A]

My missus uses salt to spot treat weeds on the lawn and it works really well so it definitely kills weeds well.
Not sure about adding it to your gaps though.
Once the salt has melted you'll be left with loose sand for the weeds to grow in.
Better off thoroughly cleaning out the gaps, resanding and then regular maintenance to keep on top of the weeds.

[Grumps]

Mmmm... interesting point about dissolved salt leaving loose sand for the weeds to grow in. I think my sand is pretty loose anyway though. I'd have thought the salt would take quite a time to leach away and provide a good weedkiller meanwhile.

What I was really want to know is, "Will it damage my blocks - which might be concrete-based?".

[Carberry]

Mmmm... interesting point about dissolved salt leaving loose sand for the weeds to grow in. I think my sand is pretty loose anyway though. I'd have thought the salt would take quite a time to leach away and provide a good weedkiller meanwhile.

What I was really want to know is, "Will it damage my blocks - which might be concrete-based?".

Yes, especially in the winter. Salt will dissolve and be absorbed by the concrete, salt attracts more water so more water is absorbed, it freezes and expands, concrete fails.
I don't know the chemical process but I also know sodium chloride has been shown to change cement and weaken it too.

It really isn't much effort to occasionally sweep your driveway in the spring / summer, pressure wash it or spray it for weeds. I would just do one or all of the above.

[Grumps]

Thanks for the info on salt's destructive power. Would the same apply to clay-based blocks?

It really is a lot of effort to clear the cracks of weeds though.. I have 90 square metres of 200 x 100 blocks. That's an awful lot of cracks to clear. It took me 2 days of really hard work and I don't want to repeat it twice a year. If weedkiller is the only alternative then it's glyphosphate and that can only be applied when in leaf and not after I've cleared it as it is non-residual.

[henpecked]

Clean it, weed it, sand it, put down weed-killer ,then seal . Job done, no more maintenance.

[Mikey_C]

groundclear is a weedkiller with a residual affect

[Grumps]

Thanks Mikey_C for the info on Bayer Ground Clear (identical to Bayer Path Weedkiller Concentrate BTW).

[Grumps]

Thanks henpecked. It still begs the question as to which weed-killer. A contact weed-killer isn't much use after it's been weeded. Also, my missus doesn't like the sealed finish - and you are not the only henpecked one ???

[Tommy]

Chikara is a residual herbicide that works up to 6 months. Add it to a usual mix of glyphosate and spray as normal.

Quite expensive for even a little tub.

We control weeds over about 800 acres, using about 30 litres of Roundup each time, every 5-6 weeks, but with chikara added, we spray twice a year and use 40 litres of Roundup in total.