Keilim 20:4

Let’s say a large trough was damaged to the extent that it could no longer hold pomegranates so it was converted for use as a seat. Rabbi Akiva says that such a trough is susceptible to ritual impurity, while the Sages say that it remains insusceptible unless one trims it. If it was converted into a feeding trough for cattle, then it is susceptible to impurity even if he attached it to a wall.

Keilim 20:5

If a seating block was attached to a row of bricks on a wall – whether he affixed it (with nails) but didn’t build over it or he built over it but didn’t affix it – it is susceptible to ritual impurity. If he affixed it and also built over it, it is insusceptible (because it’s considered part of the building). Regarding a mat that was spread over the rafters – whether he affixed it (with nails) but didn’t plaster over it or he plastered over it but didn’t affix it – it is susceptible to impurity. If it was affixed and he plastered over it, it is insusceptible (because it’s considered part of the roof). If a bowl was attached to a chest, counter or cupboard in the way that it normally holds its contents, it is susceptible to impurity; if it was attached in such a way that it can’t hold its contents, it is insusceptible.