Replacing timber lintels in rubble-filled stone wall

[minerscottage]

I need to replace a pair of lintels holding up an old stone/rubble wall above a doorway in a ~1890 (?) house. The lintels are timber and have spent many years encased in cement tanking (inside and out) and have become very damp. You can visibly see signs of wet rot; the timber you can touch is spongy, wet and there's bits of mycelium visible.

What I'm thinking of doing is using some acrow props with StrongBoys to hold up the stone course above the lintels, rip the lintels out and slide two new ones in. Once the lintels are replaced, I'd also want to prop the outside skin of stone coursework up in the same fashion so I can do some repairs to the brick archway.

Here are some pictures

The issue I have with my plan is I don't think a StrongBoy would be long enough to support the column of stonework above lintel B (centre) and C (inner). I might be able to use a StrongBoy to replace just lintel C (inner), but that would leave B (center) in place which is just as rotten as the other.

The other concern I have is that the mortar used between the stonework is an old mud mix which I doubt offers much tensile strength to hold a stone in place from above if I remove a stone below (e.g. like how a brick wall can be supported by a single acrow prop diagonally down). I'm thinking I'd need a StrongBoy to support every stone directly above the lintel, which is quite a few.

An alternative approach I've read about is people knocking a single stone out and pouring a liquid cement slurry into the middle rubble cavity, which once set provides some strength for quickly swapping lintels out. I'm dubious about that though.

It seems to me if I could get a StrongBoy that's long enough, to clear the 24cm inner lintel (with enough room to manoeuvrer a new lintel in place too) I could do it.

Does anyone have any experience with such a task?

 

[Notch7]

I’m guessing they are ceiling joists visible in the image - Its a good idea to have some acrows supporting them whilst you do it.

 

[minerscottage]

I’m guessing they are ceiling joists visible in the image - Its a good idea to have some acrows supporting them whilst you do it.

Yeah I'm going to lift a 2x4 plank under the joists perpendicular and hold up with two Acrows support them.

 

[RandomGrinch]

Is there any sense in doing some of the brick repair and repointing first, consolidating the wall? It may provide some additional strength, before messing about with the lintels?
I've recently repointed my stone rubble walls with lime mortar and the wall is now (forgive me!) Rock solid.
... and looked so good afterwards, I haven't bothered re-plastering.

 

[^woody^]

Be careful with stone walls as the inherent self-support that bricks and blocks give is not the same, so props can't be relied to work in the same way.

Neither can you rely on strong boys, which are designed to work on a single 100mm leaf.

How much support any built-in joist will provide when propped depends on how far they bear into the wall and the make up of the core of the wall.

 

[stuart45]

I normally use needles when doing work in random rubble stonework. As woody says there's a big difference in stability. The stonework to the right of the frame doesn't look to be bonded in to the rest of the wall. I would as RandomGrinch says and point up the walls first to help stabalize them. Lime mortar such as NHL 3.5 would be better for an older property.
The render on the front looks like a rock hard cement mortar, which isn't ideal for those walls.

 

[stuart45]

This wall was really unstable, especially on the corner, but a lime repoint made all the difference.[GALLERY=media, 104205]DSC00011 by stuart45 posted 30 Mar 2020 at 3:56 PM[/GALLERY][GALLERY=media, 106944]DSC00085 by stuart45 posted 20 Aug 2021 at 12:38 PM[/GALLERY]

 

[minerscottage]

Doing the repointing first does make sense. I had considered putting it off until after the lintel swap because I suspected the disturbance would cause the pointing to fail in places and require a second run.

The existing mortar is, to my eyes anyway, a weak earth-based mix which I can't imagine is giving much strength. I'll see about raking out the old mortar and pushing some NHL 3.5 in.

I normally use needles when doing work in random rubble stonework.

How do you go about pushing a needle through the wall if there's rubble in-fill in the middle? My understanding is you take a stone from both the inner and outer skin and support using a prop from both sides, but how do you handle a random (immovable) rubble stone that's blocking your way. Or am I over-thinking it?

 

[RandomGrinch]

how do you handle a random (immovable) rubble stone that's blocking your way. Or am I over-thinking it?

In my case calling the infill 'rubble' would be an overstatement!
It was anything they could get their hands on, but very loosely packed, dust, grit and a few larger stones.
It wanted to fall out of any hole I made!

 

[SammySomerset]

How did this job go in the end? I've got a rubble-filled wall with numerous timber lintels over doors and windows that need replacing so would be interested in how your choices worked out. My walls are not cut stone - they're a jigsaw of all different shapes and sizes - but they still have mortar intact, so i'm hoping strongboys will do the trick.

Very interested to know how you got on.