Replacing rotten wooden lintels supporting stone wall?

[idontknowwhatiamdoing]

I am not a structural engineer, so please bear with me

I have a cottage wall with a small window that has  three (3) wooden lintels supporting the top of it.

The wall is approx 2400mm tall and 800mm thick with random stones and a lime mortar mix.
It was constructed in the early 20th century.

 

As you can see the wood has dry rot and needs to be replaced with concrete lintels.

I have measured and found concrete lintels to replace.

My question is getting the lintels in safely.

I have looked at various techniques (spikes, demolishing the top part of the wall and rebuild)
However they all seem to use brick walls as examples

I have come across Strongboys used with Acrow Props, however they might make it hard to manoeuvre  the concrete lintels in perhaps.

Any advice on how I tackle this?

This is a rough idea

1. Double check any loose stones on the surface
2. Put lime mortar on loose parts of wall (if there are any)
3. Insert 2mm piece of sheet steel between wooden lintel and stone wall to prevent any loose bits moving or falling out
4. Try and push two strongboys between wood and steel sheet
5. With a cordless circular saw, cut out the wooden lintels
6. Clean out old mortar
7. Re-mortar
8. Insert concrete lintels
9. Finish with more mortar
 

[markc]

Strong boys are great but they are designed to support much thinner walls than yours.

Are the replacement lintels full depth? ideally you could do with replacing half and then the other half to maintain support.

Bricks are predictable, random stone and infill isnt. Unless properly supported this could go horribly wrong

[idontknowwhatiamdoing]

7 minutes ago, markc said:

Strong boys are great but they are designed to support much thinner walls than yours.

Are the replacement lintels full depth? ideally you could do with replacing half and then the other half to maintain support.

Bricks are predictable, random stone and infill isnt. Unless properly supported this could go horribly wrong

Its weird, the three wood lintels only support 2/3 of the wall

On the outside there is a concrete lintel which supports the other 1/3

Its as if they made it look nice on the outside, then used wood for the internals that were hidden.

Pictured

 

 

Edited March 15, 2021 by idontknowwhatiamdoing

[markc]

@idontknowwhatiamdoing this makes it easier as the outside lintel will stabilise the wall and take most of the load.Use strong boys to be doubly safe. a couple near the center shouldn't cause too much hassle getting the replacements in

[Russell griffiths]

Just a tip to make life easier. 

Place the concrete lintels tight to the face of the wall up of the ground before you install the strongboys, this way they are half way into position and you don’t need to thread them through the acrow props. 

[Moonshine]

I did this last year, i managed to replace two well rotted lintels in a single day (crap brickwork :)).

I used a single strong boy further up the wall, though i don't know the best place to put it in your case.

 

[jfb]

18 hours ago, idontknowwhatiamdoing said:

4. Try and push two strongboys between wood and steel sheet

I would put the strong boys a bit higher up and accept that you are going to have to do some remedial filling in above the concrete lintels.

It might be hard to get the lintels in if the stongboys are this low since the angled support for the strongboy can get in the way and you also need room to get the lintel onto the mortar beds.

 

 

[markc]

1 minute ago, jfb said:

I would put the strong boys a bit higher up and accept that you are going to have to do some remedial filling in above the concrete lintels.

It might be hard to get the lintels in if the stongboys are this low since the angled support for the strongboy can get in the way and you also need room to get the lintel onto the mortar beds.

 

 

In Random stone it is almost impossible to get then in higher without cutting slots that will glare at you later. Concrete lintels can be a bit thinner than the wooden ones (assuming they have rebar in them) allowing you a bit of wiggle room to pack fill either side of the strongboy before removal.