You need one item.
That item is salt.
Step 1: Small Amounts Cast Around
Every three feet or so, throw a pinch of salt.
Carpeted or uncarpeted. Floorboards or tiles - It doesn't matter.
Walk around inside of each room, throwing a pinch of salt down as you walk, every step or so.
Kitchen, bathroom, bedroom, laundry, garage - each room.
Then the hard-to reach places, just a pinch will do: on top of and inside kitchen cupboards, and behind the refrigerator, drawers, under sinks, all shelves and clothes wardrobes.
In the bathroom, pour a little down the sinks and drains.
That's it. Your done.
You won't see them again.
Step 2: Now for the Questions...
You mean I just walk around the house, sprinkling salt, and the cockroaches are gone?
That's exactly what I mean.
How come no-one's heard of this before?
I don't know.
'I don't want my house with salt all over the place!
You won't see or step on any salt. This is probably the major "issue" with this process. People think they have to turn their place in to a salt mine, with salt caked along the walls and they will notice it.
Roughly, a teaspoon of salt is enough to do an entire average-sized home including the pouring of some down drains and sinks.
You won't notice the salt.
'How much salt do I need to use?'
Standing about a metre away you would flick one pinch of salt for every 1.5 metres (or five feet) of where the wall meets the floor.
One pinch flicked in cupboards and wardrobes. A little down drains and sinks. It doesn't have to be perfect.
'Will the salt stain my carpet?
Excess salt is sometimes used to soak up liquid carpet stains, and this isn't excess. It's not a liquid. It doesn't stain.
'Can you guarantee I'll never see another cockroach again?
There are no guarantees in life.
When you first scatter the salt, if you have a lot of cockroaches, 99.9% of them will exit the house, pronto. Later that day or night, you may see one trying to find a spot where there's no salt. After that one is terminated with extreme prejudice, you will be cockroach free. Is that a guarantee? Mmmm...
'Why do the cockroaches go away?'
Interesting question. I think it may have something to do with salt adversely affecting their digestive system. Arthropod physiology, huh? It's a wonderful world.
'Salt doesn't kill cockroaches!
That's right, it doesn't.
It repels them.
'How long does it last?
Until you vacuum, or sweep or wash the bathroom floor, or clean the cupboards. After any of these, you will have to do it again.
'If this works, why are there multi-billion-dollar companies selling cockroach baits and poison?
Not sure. Baits and poisons attract, and the theory is that cockroaches eat the bait and go away to die. That's the theory.
Grains of salt are a cockroach repellent.
'Where else can I use it?'
Car. Taxis use it. Buses. Please don't eat or drink on public transport. It attracts cockroaches. Restaurants. Hotel room. Your parent's house. Fast food. Anywhere cockroaches are a problem.
'Does it matter what type of salt I use?'
I've never tried it with any kind of flavored salt so I'm not sure about those. I have done it with:
Ordinary table salt out of a plastic shaker.
Iodized table salt out of a plastic shaker.
Sea salt ground out through a salt mill.