Crumbling render behind wallpaper

[dodger007]

I first noticed a bulge in the wallpaper in my lounge just below the coving. Giving it a prod it felt like the plaster behind was crumbling so I stopped. I don't want to peel back the wallpaper as I have no intention (or time) to redecorate the lounge. I then checked the small bedroom above which had been used as a storeroom by our son when in between houses. The wall had had a double size foam mattress against it and when pulled away showed a similar but larger bubble just above the skirting. As this room will be decorated soon I pulled all the wallpaper away. The plaster and what looks like sand & cement (?) render all crumbled away in an area about 8 in wide an 6 in high. It also had crumbled away below the skirting. Two questions:
1. Any idea what could cause this?
2. How should I repair the fault, firstly in the bedroom. I don't really want to have to rip the skirting off.
Any ideas please?
House built around 1907

 

[Tigercubrider]

it just sounds like the top skim has blown.

you could pay a plasterer to skim the whole wall, or try yourself to skim just the affected area.
Either use proper plaster , or easifill which is easy to work with, if you have a trowel or speeder larger that the hole that you're filling.
Use the existing plaster as a guide.

if time and lack of mess or finish is important, get a plasterer.

 

[dodger007]

Thanks tiger. All rendering crumbled away back to brickwork including behind skirting - and below I guess as it's apparent in lounge below.

 

[dodger007]

Should I just try and shove some form of filler down behind the skirting board, then build up layers on the wall? I'm not a plasterer (I discovered that many years ago!) and not after a professional job. This is just a small bedroom and will be papered at some time soon.
I have some Artex which I use for filling patches on the walls, shall I try to get some of that behind the skirting first?

 

[Tigercubrider]

I am a diy' r but think bonding plaster is what you need to fill the big gaps.
It has sticktion

 

[vinn]

OP,
Is the wall in question a solid or a cavity wall?
Is there render on the outside?
Was there a musty smell in the bedroom?
Was there any staining on the wallpaper in either room?

Why not remove a length of the bedroom skirting, and examine the back of the skirting for decay?

FWIW: your 1907 "plaster" will be a sand and lime mix.

 

[dodger007]

Thanks for that Vinn. It's actually the party wall with my neighbour! It started as an old 3-bed semi-detached 'cottage' with two rooms downstairs and an 'outhouse' for laundry/toilet. It's seen may mods and extensions since then though! So, to answer your questions:
Possibly a 'rat-trap' cavity wall (small gap)
No render on other side.
No musty smell. I know what this smells like!
No staining on wallpaper upstairs or down.
It just seems like the material behind the wallpaper has lost any bonding to itself and is now dust.
Yes, it is very 'sandy'.

I feel quite confident there is no decay (from damp) on back of skirting. It's the 'box' room so very small and a length of skirting will stretch from wall to wall.

Maybe I'll follow Tiger's suggestion and get some 'bonding' plaster and whack that down behind the skirting and smear some on the wall.

Actually, when I get around to decorating this room I might have a floorboard or two up to see below the skirting.

Thanks all.

 

[dodger007]

So, is this just 'age' that caused the render/plaster to 'blow'?
All walls in the original building are papered because the 'plaster' (sand & lime?) beneath isn't very sound.
Thanks.