Scary Gap/hole in stone built walls

[sb1202]

Just pulled back some plasterboard to discover a significant gap in the stone walls. It's a trad scottish rubble fill wall that was converted around 40 years ago. There's no fallen stones or dust in the cavity floor which suggests it was left this way when the work took place. The stones aren't damp or wet but the brown clay like stuff is slightly damp - ie will form a lump when squeezed. Is this something to worry about and is it something I fix or fill myself? (I'm not a brickie, stone mason) Everything else around it seems to be solid.

[ProDave]

I would certainly rebuild it and re point it, just so it looks right.

 

I love the way the old shelves got boarded over, still with stuff on them.

[saveasteading]

1 hour ago, ProDave said:

rebuild it and re point it

It  is a standard construction and cracks are normal. You pack the gap with stones in lime mortar, using as big stones as you can fit in , then smaller so that the mortar is minimal.

Must be lime, with the grade selected to be just softer than the stone. Granite/ limestone/ sandstone??

 

removing the mud and replacing it with masonry is advisable, as long as it remains stable all the time.

Do you think the crack was there when they hid it behind the stud? The absence of rubble on the floor suggests it was.

 

Is there a crack on the other side?

[sb1202]

2 hours ago, ProDave said:

I love the way the old shelves got boarded over, still with stuff on them

I know - you can guess my reaction. 

[joe90]

Talk about a plasterboard tent 🤷‍♂️, that’s crazy. It will keep you busy for a while. 

Edited 17 hours ago by joe90

[sb1202]

41 minutes ago, saveasteading said:

Must be lime, with the grade selected to be just softer than the stone. Granite/ limestone/ sandstone??

It's granite.

 

42 minutes ago, saveasteading said:

Do you think the crack was there when they hid it behind the stud? The absence of rubble on the floor suggests it was

I think so.. There's no crack on the other side of this side but there is a crack on the outside of the wall to the left . From what I can gather, this was a self build by a quantity surveyor who (the locals say) had a reputation for cutting corners. He certainly cut this corner by the looks of it.

[sb1202]

17 minutes ago, joe90 said:

Talk about a plasterboard tent 🤷‍♂️

You'll need to excuse my ignorance but what exactly is a plasterboard tent? 

[joe90]

5 minutes ago, sb1202 said:

You'll need to excuse my ignorance but what exactly is a plasterboard tent? 

It’s a term used here when plasterboard is stuck on a wall rather than solid plaster but not properly so draughts exist behind it. As @saveasteading says above best infill those gaps. What are your intentions regarding finish.

[Redbeard]

It describes a 'syndrome' where you get unwanted cold air circulating on what should be the 'warm side' of the wall lay-up. The most typical manifestation is 'dot 'n' dab' - plasterboard fixed to a wall on blobs of adhesive with lots of hollows between. Any air leakage through gaps in the wall may get through to those hollows - That is a 'plasterboard tent'. In your case I think @joe90 was referring to the apparently very (air-) leaky stone wall with the void betwen it and the hollow-fixed pl'bd. *Ah! I see @joe90 has just replied. I'll post this and maybe find we have said the same thing!

[sb1202]

1 minute ago, joe90 said:

It’s a term used here when plasterboard is stuck on a wall rather than solid plaster but not properly so draughts exist behind it. As @saveasteading says above best infill those gaps. What are your intentions regarding finish.

Ah. This isn't PB stuck to the wall though. This is a stone/granite cottage 600 thick. The PB sits on stud walls about 150mm from the main walls which are pegged to leave the void. 

I'm stripping back all the internal PB, building new studs and insulating with wood fibre. Breather on the cold side and intelligent membrane on the inside. Will plasterboard over it again.

[saveasteading]

3 minutes ago, sb1202 said:

The PB sits on stud walls about 150mm from the main walls which are pegged to leave the void. 

Which is what we built on purpose.  The stone wall has a recognised U value  (0.6 springs to mind) , as does the gap, but not  a lot. 

We built a stud wall of 100mm with membrane on the back and insulation in the gaps, then a plastic inner sheet. then the service gap helps too. A recognised solution and working really well.

[Redbeard]

22 minutes ago, sb1202 said:

Ah. This isn't PB stuck to the wall though. This is a stone/granite cottage 600 thick. The PB sits on stud walls about 150mm from the main walls which are pegged to leave the void. 

 

Yes, I gave the example of 'dot 'n' dab', but if there is any external air-leakage into the cavity behind the plasterboard then you have brought the 'outside inside, and potentially you could have just a half-inch of plasterboard between you and air at external temp.

 

I was going to suggest insulation, but @saveasteading already has. I more usually used to insulate 'hard to the wall' on a lime parge coat, but fixing through granite sounds like it would be ... fairly challenging!

[sb1202]

15 minutes ago, saveasteading said:

We built a stud wall of 100mm with membrane on the back and insulation in the gaps, then a plastic inner sheet. then the service gap helps too.

That's what I'm going for. I'd like to include the service gap but the rooms are already small. Adding 25mm battens plus 9.5mm PB for a service gap will bring the rooms by an extra 70mm so I need to give this some thought. 

[Redbeard]

Have I misunderstood? I thought you said your studding was 150 from the wall. A reasonable gap would be 50mm, so you could get 100mm insulation in and add a service void while losing 40mm at most. If you are prepared to have wiring on internal walls only you don't even need that.

Edited 16 hours ago by Redbeard

[joe90]

46 minutes ago, sb1202 said:

The PB sits on stud walls about 150mm from the main walls which are pegged to leave the void.

So you will gain room by reducing, at least, that 150mm.

 

47 minutes ago, sb1202 said:

Ah. This isn't PB stuck to the wall though. This is a stone/granite cottage 600 thick. The PB sits on stud walls

Same principle tho, leaky wall and plasterboard (however fixed) inside it.

 

42 minutes ago, saveasteading said:

We built a stud wall of 100mm with membrane on the back and insulation in the gaps, then a plastic inner sheet. then the service gap helps too. A recognised solution and working really well.

Our man @saveasteading has been there, done that, with good results so bodes well for you.

[sb1202]

1 hour ago, joe90 said:

So you will gain room by reducing, at least, that 150mm.

 I won't because the walls are hugely uneven. This is a classic Scottish stone wall cottage from the 1800s - which is a bit like a tall dry stone dyke with a roof on it. The internals are made from large rocks and the gaps from stud to wall range from 150mm to 50mm. The existing studs are only 50mm deep, so when I'm building the new stud walls from 4x2s, it's bringing the walls in by around 40 mm

Have a look at the image attached - it gives you an idea of what the walls are like.

[Mike]

3 hours ago, sb1202 said:

what exactly is a plasterboard tent?

 

3 hours ago, Redbeard said:

if there is any external air-leakage into the cavity behind the plasterboard then you have brought the 'outside inside, and potentially you could have just a half-inch of plasterboard between you and air at external temp

 

And here's an extreme illustration: - this is what happened when I cut a hole through some plasterboard to rescue a bird(!) that was trapped. The 100mm glass fibre insulation behind the plasterboard was pretty pointless.

 

 

[ProDave]

49 minutes ago, Mike said:

 

 

And here's an extreme illustration: - this is what happened when I cut a hole through some plasterboard to rescue a bird(!) that was trapped. The 100mm glass fibre insulation behind the plasterboard was pretty pointless.

 

 

Seen it regularly.

 

In MOST houses, take a light switch off the wall on a windy day and you get greeted with a blast of icy cold air coming out.  Unless the house is build properly air tight, then all the voids are usually linked by cable and pipe holes all leading to the cold loft.

[saveasteading]

2 hours ago, sb1202 said:

the image attached

I forgot to look at the walls when I saw the view.

[Redbeard]

I had based my comments (as had @joe90, I think, on your post above:

 

5 hours ago, sb1202 said:

The PB sits on stud walls about 150mm from the main walls which are pegged to leave the void. 

 

So 150 is the max, but due to the random wall construction it goes down to 50? I now understand why you are concerned about losing more space.