Repair/replacement of overdrilled wall

Question

After taking down one of those cantilever "invisible fixing" Ikea LACK shelves, I discovered that there were twice as many holes in the wall as required and all of them were enlarged and ruined (the wallplugs were very small and cheap). The wall is an interior one and it is a fairly thin coat of plaster over what appears to be fairly soft cement-like material. The underlying material around and between the holes is so damaged you can pick it out with a finger.

This means that at each end there are eight very closely spaced holes and a group of 4 in the middle. The wall is now unusable for shelf fixing in this area as there's hardly any plaster left, and the plaster around the area is flaking off:

I know I could clean the holes out, fill them with filler, sand and paint (the room will be repainted anyway soon), but I am concerned that this will leave fairly large hidden weak spots in the wall. Is it better to chop out the affected areas of wall, back to solid material and fill in with something stronger than filler?

EDIT: It's a 1930's house, and I suspect the wall is original. I haven't found any brick so far but there is some hard grey cement-like material behind the plaster that seems pretty solid. This is the best photo I can get down the hole after raking out the worst of the loose material (the "island" between the four leftmost holes collapsed, leaving one big one!)

Answer 1

I see no benefit to cutting a section out of the wall before patching it up. You don't say how old your house is, but in the houses I've lived in that are nearing 100 years or so, the plaster can weaken to the point you can pull it apart with your fingers if you damage the surface somewhere.

If that is indeed a coat of plaster/insulation on top of the structure of the wall, nowhere will be load bearing and you will want to drill into further the brick/breezeblocks/studs anyway.

Filler will work for those holes. If though after cleaning the loose bits away you are really worried they may be too large for filler, when I have large sections to fill I:

• Clean the area with a wire brush.
• Fill out with typical multipurpose/'one-coat' plaster.
• Then a thin layer or two of pre-mixed finishing plaster, sanding in between.*

After painting it's invisible no matter what the damage.

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EDIT: TDHofstetter makes a good point. I can't assume thats plaster over brick from two photos. From experience though, what may seem like an extra hour or so digging back to solid material to do the best job possible, can quickly turn into a whole weekend replacing 2/3rds of your wall! If the wall is otherwise fine, and unless you know you are going to want to mount something to that area, I would still suggest filling it and coming back to it when you need to.

Someone might offer better advice if we knew the structure of the wall though, could you maybe drill further in to see how deep this layer goes, and what, if anything, is behind it?