[fudgieoto]

Just to add to the posts above, you could use intonaco ( plaster) depends on the area size you are going to replace.
(There 3 main types 1) yw 10 this is an external/internal rough 1st coat plaster.
2) yw 12 this is an external fine finishing plaster.
3 ) yw 13 a fine internal plaster used for finishing.
If you just go to a builders yard and ask for intonaco 10 you will get no 1. Comes in 25kg bags at around 3e a bag.)
Old render that has blown should be removed.
If the area behind the render is damp, let it dry out.Then dust the area down, allowing for you to apply a wash of sealant. PVA glue mixed with water should be good. It will help key the remaining render and provide a good surface for the new plaster to be applied. This allows for the plaster to dry not to quickly, or get the life sucked out of it. It allows time for you to work with the product.
When this has dried you can paint.

If you go to a good diy store here in italy, you will be able to by all different types of filler, some for wood, metal, plastic/fibrsglass kits. hope you get my drift.
Basically, it is knowing the italian for most of it.

Fillers can come in powder form, that you mix to the consistency you like before applying, or the ready made in a pot, ually 500g or 1kg.