Why have weeds re-grown after several weeks?

Only deep-rooted rhizomatous weeds may re-grow. This will only happen if too little Roundup has been allowed to penetrate the full plant system. In this instance, a re-treatment will be required.

Why has it killed the grass?

Because Roundup is a non selective weedkiller, that means that Roundup is very effective at killing all plants. So be careful to only spray weeds or plants that you don’t want to keep.

Can it be used on paving?

Yes definitely, Roundup is ideal for use on paving, paths and drives as it penetrates right to the weeds roots to ensure a complete kill.