If moss is a weed why can't you kill it or is it a fungus?

These plants commonly like to grow in outdoor carpets:

liverworts - http://www.google.com/search?q=liverworts&oe=utf-8...

moss - http://www.google.com/search?um=1&hl=en&safe=activ...

Blue green Algae ( a bacteria) also grows on carpets if it is in sun.

I do not think putting lime on the carpet is going to do the carpet any good, but if its not meant to be attractive, lime will kill many of the above organisms.

Keeping the carpet dry would be a preventive measure.

A steam sprayer with hot water can be used to kill them and wash then out of the carpet.

Technically I don't believe it's a fungus, but more like lichen, which can grow without needing soil for nutrients. That may be why a normal weedkiller won't work, but you may be on the right track, i.e. a fungicide. Most fungicides use some type of chlorine solution, which will kill moss too. You'd probably be best trying to mix your own solution using bleach, and figure out the weakest solution that would work without taking the color out of your carpet.

It's not sun, but dryness you need to kill off moss.

In any case, if you're unwilling to move it, you're basically stuck out. You need to thoroughly scrub it on both sides, then spray it with 20% vinegar, then let it dry COMPLETELY. Even so, moss will probably still return after a heavy prolonged rain.

BTW, moss is a plant. Not sure if you're talking real moss or mildew or algae.

You can kill it. Spread lime. One cause is a pH problem.

Or follow the other answers you got yesterday. Sometimes, not much CAN be done