If you mend something over and over will it ever just not work or can you mend things over and over even after you've turned them tattered and worn or stuff like that. Also can splendor robes be mended? Also does effective go away if things become tattered? I've heard from Asmodea I think that tattered robes were still effective, she was getting new ones cause she's the white witch and you can't look like one with tattered robes! but just wondering if anyone else knew about it.

You can mend splendour robes. I think there's a limit to how many times you can ultimately mend clothing, but I don't think anyone ever hit it.

There is, I hit it on a pair of shoes once. It depends on how many months the item normaly has.

If robes become tattered are they still useful?

Tattered robes still retain their defences, proofings. The only thing that changes is that they no longer add to your presence as royalty.