Blow torch

A few weeks ago when I was just working from home in our temporary apartment, I head a really strange sound from the courtyard, with an accompanying sound... sort of like water rushing. I looked out the window and found the following:

Which, if you can't make it out, is a guy using a blow torch to scour the weeds from between the cobblestones. Here's a better picture of the blow torch:

Nobody likes weeds, but this seemed like a rather strange method of clearing them away.