Sandstone lintel repair options

[Van Bergan]

Dear all, I'm looking for ideas on how an in situ repair could be done on a couple of cracked sandstone.

I suspect that both have cracked due to their relatively large spans (~1.7m and ~1.4m), that said the respective cracks have not telegraphed through the supported brickwork (bar a single brick) and I imagine these cracks are many many years old., the overall condition is structurally sound.

I would leave the lintels as they are (save some cosmetic filling) however the windows below both lintels and being replaced and that offer an opportunity to do a structural repair.
From reading @Feltwell post here I understand that stainless steel bars may be drill and epoxy'ed through the crack (I assume at a 45 deg angle).
Due to the carved mouldings I'm somewhat limited to where I can drill which may mean I cannot position the stainless steel bars exactly mid lintel thickness

Just wondering if anyone has done a repair job similar to this and could provide some helpful tips. IS the helifix type twisted bar a good choice.
I'm a carpenter by trade, so relatively skilled at craft and the property is my own.

 

[Van Bergan]

I've actually found the imagine below from the website of a repair company.
This is how I imagined the bars are postioned although given the mouldings on my lintel the drilled holes and therefore bars will likely pass through/against one another which I dont think will be an issue.

 

[Cubist]

Hi There,
Feltwell occasionaly pops in and may be along to offer some direct advice but Stevers too I think has some relevant knowledge/experience. Whilst I'm familiar with this 'stitching' approach I have never used it with stone so will not comment further other than to say that in my opinion its best to use stainless steel as rust could induce considerable damage to the stone later.
Cheers and Good Luck,
Cubist

 

[a twig]

Will the window removal allow you access to the back of the lintel / head?

If so you can chase out two deep grooves in the back - insert stainless steel rod (at least 150mm either side of the crack) in the chases and then pack in NHL3.5 mortar back to the surface level.

If you are really keen you could do the rods full width.

I’ve also seen the same approach done from the front but using a block of matched stone mortared in to fill the chase - instant “feature”

 

[Van Bergan]

Thanks to both for your response.
I actually got up on a ladder this evening for a closer inspection and there is a bit of play across the face of the crack in the lintel.

Although I think stitching from underneath at a 45 deg angle would prevent the lintel from dropping further I cant see it offering much support across the face of the lintel certainly not at the bottom or top edges as the bars will only bridge the crack at the centre of the crack.
In that case any cosmetic filling wont last too long.

A new lintel is an option however lead times and ensuring the carved mouldings match existing will take some time and attention.
@a twig I can't access the back of the lintel but I do like your idea of repair. I could, and would be prepared, to remove the lintel lay it up on the scaffold and then make the repair to the back of the lintel.

I imagine given the relatively large span the SS rod would need to be at least 10mm diameter.
Would NHL mortar suffice as backfill, I had though epoxy would have been required?

 

[a twig]

If you’re happy and capable of doing that then yep that’s definitely the best way to do it.

I’d only suggested NHL mortar as it’s easier to play with sands / stone dust to colour and finish match.

If you’re prepared to go the whole hog and it will be invisible then yep an epoxy would definitely do the job - you can get ones like this that are made for the purpose

10mm should be plenty thick enough as it’s reinforcing the existing stone not trying to take the whole load

 

[a twig]

I was trying to find a picture online and accidentally stumbled across basically a step by step guide if that helps

If it were me I wouldn’t have repaired the visible bit in front with the same grey goop though

Stone window Lintel repair specialists in Kent

Cracked stone lintel repairs and cracks around window frames with related movement problems all repaired by our specialist contractors in Kent.

actionwallties.co.uk

 

[Van Bergan]

Yeah I will be able for the task, I do quite a bit of structural alteration work and I'am well geared up for it.
With the repair at the back of the lintel and unseen I think a tub of that epoxy is the ticket.

One last question, should the cracked faces be buttered with some manner of material before reasembling?
Not sure if mortar would be suitable, can imagine the sand grains hindering a tight meeting of the faces back together, perhaps a lick of epoxy? Although in practice does it add anything to the joint.

I actually saw that article you linked and I am in Kent.
It reminded me exactly why when tasked to find a solution to a problem I know little about, I prefer to research and have a go myself rather then calling in the "pros"

 

[a twig]

Yeah that article did give a “we’ve done the hard bit so let’s get out of here” vibe particularly towards the end

Probably no harm in buttering the ends with the same epoxy, but you’re right that it won’t make a huge amount of different.

When it’s all installed I’d open out the crack on the face a bit and repoint it with NHL mixed with all the stone dust you’ll have left over from chasing out the back, that way the repair should end up pretty much invisible from the outside.

 

[Stevers]

Normally when there's a moulding like that in the middle of a lintel it's because there was something underneath it holding it up. and that does look to be a longish span for a stone lintel without intermediate support. The 45 degree stitching, cunning as it is, wouldn't really address that problem. The lintel will have bending forces on it from the triangle of masonry above it increased by any failure of the inner lintel. The tensile strength of the natural stone will be limited, hence the cracks. Permitted spans for natural stone are likely to be empirical, based on experience, and that experience probably isn't around any more. Whilst you're replacing the inner lintels, I think I'd consider fastening a heavy stainless steel strap on the back of the lintels towards the bottom edge fastened with masonry bolts to add a bit of tensile strength and tie the two halves together.

I did do an epoxy and reinforcing rod repair to a fireplace upright, but I used CCC wood repair epoxy as it was to hand. That epoxy is intended to have some flexibility to cope with movement of the wood, and whilst I wouldn't trust that repaired upright as a beam, I had no problems with moving it around or lifting it into position after repair.

 

[Van Bergan]

Normally when there's a moulding like that in the middle of a lintel it's because there was something underneath it holding it up. and that does look to be a longish span for a stone lintel without intermediate support. The 45 degree stitching, cunning as it is, wouldn't really address that problem. The lintel will have bending forces on it from the triangle of masonry above it increased by any failure of the inner lintel. The tensile strength of the natural stone will be limited, hence the cracks. Permitted spans for natural stone are likely to be empirical, based on experience, and that experience probably isn't around any more. Whilst you're replacing the inner lintels, I think I'd consider fastening a heavy stainless steel strap on the back of the lintels towards the bottom edge fastened with masonry bolts to add a bit of tensile strength and tie the two halves together.

I did do an epoxy and reinforcing rod repair to a fireplace upright, but I used CCC wood repair epoxy as it was to hand. That epoxy is intended to have some flexibility to cope with movement of the wood, and whilst I wouldn't trust that repaired upright as a beam, I had no problems with moving it around or lifting it into position after repair.

Good info @Stevers.
All the lintels in the house have that moulding (this particular one being the longest) and I'm certain there wasn't any intermediate support under it at any stage.
The inner lintel is a 6x3 timber beam with 9x2 joisting notched into it. It has bowed down ~5mm from straight so hasn't deflected much in 150 years (grant it it was likely installed crown up if anything).
Regardless the timber lintel is it good condition and I wont replace it.

I think the addition of the ss strap is a good idea, t'wud take 10 minutes extra to do but add a lot of tensile strength as you say.

I also thought about housing the the ss rods into the lintel with a camber, basically adding in the princple of an arch to provide a little more resistance to bending, as per sketch below, Although it probably isn't necessary, as your experience is the epoxy bonds there'll be little movement.
I'll post up pictures of the work underway.

 

[Stevers]

Agreed that the lintel of the window with the central sash doesn't look it could have ever have had a centre support.

The cambered rods might be better up the other way as so that they add tensile strength as the bottom of the lintel is where the tensile stress is greatest. The stone won't be short on compressive strength, so no need to try to add any of that. In addition to the strap, they would be useful to generally stiffen things up, straight or cambered, smiley or frowny. This is sounding like a repair that's in a safe pair of hands!