Weedkiller

twopenny

For what you describe good old weedol works every time. Do crush the weeds lightly before use as it says.

I also put some of the mix in a spray bottle for spot use.

I use it late evening when the birds aren't feeding and it is dry long before morning. Or stay working close by so nothing comes near.

On block paving I use a wire brush then a diluted soloution of bleach which is quicker and does the trick.

Woolsery

One of the main ingredients in Wedol is glyphosate, though they also use the brand name to market strong vinegar in ready to use form as Weedol Gun. Wouldn't fancy it on my chips though!