There is no permanent solution to "weeds" growing in places like brick patios. What happens over time is that material the "weeds" can germinate in collects in hte space between the bricks, even if those bricks are set in mortar, and those "weeds" then grow. To keep that from happening that soil must be cleaned out of those spaces. Where bricks, or any other material, is simply laid with some sand worked between them that means picking up the patio, cleaning even the base material of "weeds", resetting the material, and refilling the joints with clean sand. That will help keep "weed" growth under control for 4 to 5 years.
You can pollute your environmant by spraying "weed" killers which will stop the green growth but will leave you with dead, brown material to remove.

You can try dumping boiling water on them. Salt might or might not work, depending on the weeds, how much you use, whatever. But it will wash into your lawn or flower beds, so probably not a good idea. It would also not be permanent because it will dilute/wash away. Weed killers are not permanent. If you can get moss to take the spaces, that can help but occasional weeds will still show up. It's also difficult to grow moss only between bricks. When it gets on the surface, it's too slippery.

The farther apart the bricks are, the more weeds you will get. If the gaps between bricks are more than very thin cracks, it will be an almost constant battle. Sweeping in fresh sand in the spring can help - if it doesn't have seeds in it.

I sprayed mine with Round up. It wasn't a permanent solution, but I only needed to do it twice last season. After scraping the heck out of my hands pulling weeds, it was highly satisfying.

You might consider spraying straight vinegar on the weeds, especially on a hot, sunny day. Vinegar is often touted as a pretty good herbicide.

Vinegar should be used with caution and some knowledge for various reasons. Not all plants are succeptible to death by vinegar, so determining what weeds are present and whether or not vinegar will kill them might be a good first step. There are many discussions about it on these forums, especially the organic one. Jaggudada asked about a "permanent" solution and vinegar is notoriously unsuccessful without repeated attempts, so I didn't find it worth mentioning.

But I'm glad rhizo brought it up. Asking about using salt could be an inference of desire to find a more natural solution than a store-bought spray bottle of 'cide. I just blew past it because of the word "permanent" and was babbling about how "permanent" isn't possible. Thanks for rounding-out the discussion, rhizo. :+)

Fairly extensive discussion

What about trying a two step process...

1. Killing weeds with vinegar/dish soap mix
2. Once everything browns and is removed, spray with a pre-emergent solution like trifluralin.

I've linked a product below that is relatively inexpensive and provides up to 3 months of protection

Trifluralin is the same stuff that is used in Preen Weed Pre-Emergent Granules. Trifluralin will not damage existing plants and is relatively non-toxic (except if you're a fish).

smithmal

Here is a link that might be useful: Vegetable and Ornamental Weeder Size

Why not just clean out the soil these plants are growing in? Then there would be no need to spend money on plant poisons.

I've got a 50 foot long walkway with brick pavers in sand. Easier said than done....