Many, many failing lintels from my 1895 semi..

[Bullet-Proof_Biscuit]

Hello,

This is my next project, as you can see every single lintel is forked..

I would like to acro above each, remove the loose bricks, and rebuild, with an appropriate lime render, happy to do things the hard way, cutting bricks into tapers to make a nice strong arch for an original fix.

However..

It seems that originally, only the centre key brick was ever cut in a taper, giving a very shallow arch, which I'm guessing is causing the failures. I just now noticed the one first floor lintel has a steel arch strap lintel... Would this be original and as fitted to all the others? Because if it is then I'd happily replicate that detail on all of them (noting it will make the brick install easier too).

I can only think the arch lintels were shallow for the sake of speed or cheapness, and therefore it may not be the best original detail to reinstate??

I have found arched, galvanised catnics which are an option, but I would like to retain the visibility of the brick within the window reveal if possible, and I would like to fit sashes so a check reveal is needed (don't think that is possible with this catnic).

Also I am not sure what the inner lintels are, possibly/probably(?) timber.. They would likely be replaced with pre-stressed concrete types I guess.

It is remarkably hard to find anything online detailing a period correct, sympathetic rebuild of such things, all I find is those helifix glue-in steel rods which are obviously a nope..

I guess the thing is if I cut taper bricks for a more 'arched' arch, then the inner lintel would be visible and that would look terrible..

Am I on the right track by reinstating the steel straps? (I can have these fabricated cheaply, and naturally would galvanise & paint black per original). I do like the idea of rebuilding into original self-supporting arches though, by making plywood forms as per one of the images I attach.

Any experience or input or general thoughts would be greatly appreciated. And as an aside, the cement pointing is coming off to be replaced with lime, and I think I would like to use lime putty, would this work? The other option would be NHL 3.5 but it's got P
ortland cement in and I want to have no cement anywhere near the building after the abomination that is the cement render on most of these beautiful buildings on this street..

TIA!!
Regards,
HH.

This is the form type I would use (note all the bricks are full though?)

 

[JohnD]

In your house, surely there is a wooden lintel supporting the inner bricks?

Should be visible if you pull off the cracked plaster. May be rotten if the roof has leaked.

What is wrong with your existing shallow arches?

 

[^woody^]

That strap is a retro-repair and not required for an arch.

Technically, those arches are wrong as there should not be a cut brick in the middle. Each brick should be correctly and evenly spaced. You wont be able to cut bricks in to voussoirs as the arch is segmental and too shallow.

There's no reason why these can't be rebuilt to the original shape. Defective brickwork above should be rebuilt too.

 

[Bullet-Proof_Biscuit]

Gotcha!! Voussoirs! Thank you, now I can find all the tutorials with the correct keyword!!!

Understood no straps required.

So the bricks ARE supposed to be all evenly cut..

Cue many Youtube tutorials to watch this evening...

BTW I'm only assuming the inner lintels are timber and I'll replace as required.

Yes I would rebuild all loose brickwork local to lintels at the same time, am I wrong using lime putty? The long cure time is fine, I just leave the forms in place for however many days/weeks, my curiosity was the compressive strength would be satisfactory for an arch in compression?

Thanks again and many happy returns!

 

[stuart45]

The problem with building in pure lime putty is that the outside 10mm or so carbonates first and the CO2 finds it harder to get to the rest of the mortar.
The advantage of using NHL is that it partly sets by hydration. NHL shouldn't contain any OPC. I used it for quite a few years without any issues.
If you want to cut bricks for a arch it's an idea to draw it out full size if you can, although nowadays people can get the sizes on a computer.
There are firms that will work it out and cut them.

 

[tony1851]

For 'shallow' (low-rise) arches like yours, the bricks would normally be uncut, and the 'wedge' shape would be taken up by the mortar joints, being thicker at the top than at the bottom. In more careful work, the bricklayers would know exactly how many whole bricks would be needed to span the gap, allowing for the thickness of the mortar. This avoids having to shape the 'keystone' brick, which can look like a bit of a botch.

The problem with these shallow arches is that they need reasonable abutment each side to maintain the bricks in position. Even slight movement (common in old buildings) will cause one or more bricks to drop.

 

[Bullet-Proof_Biscuit]

Right. Does the slow carbonation of the mortar not exposed to atmosphere just mean a very slow cure sufficient to be self supporting? It won't be occupied for a few months so that would not be a problem. Fair point well made though, I can consider NHL now at least thanks.

For the sake of a dozen bricks per arch I would like to cut them all for architectural & aesthetic correctness, and as mentioned because I like to do things the hard way..

Fortunately there seems to be lots of tutorials on calculating the arch, basically the lengths for the intrados and extrados, divide by brick header dim to get brick quantity, and minus 10mm mortar bed for each. Sounds like an interesting project to me!

All openings have sufficient abutments to prevent movement, on the rear elevations at least, the front bay is single storey and might need a different solution..

Sound reasonable???

Thanks again!!

HH

 

[stuart45]

The old method was to get a large board, some straight edges and a beam compass points with a length of 2x1. Draw out the arch and then draw in the joints. You can then make a template and cut the bricks. You can then place them on the drawing and see how the finished arch will look.
With pure lime it won't carbonate as well once dry, so the back of the joints may not harden properly.
In the older days lump or hot lime was used on sites, which expanded when mixed and was also slightly hydraulic.
Or use this.
Masonry Brick Arch Header Calculator - Metric (blocklayer.com)

 

[Bullet-Proof_Biscuit]

Much appreciated! That's solved a whole lot of measuring! Bookmarked...

Arch Radius 1114
Arch Sweep Angle 34.5°
Arch Spring Angle 72.8°
Unit Bottom Width 51
Unit Top Width 63
Units 11

On the topic of mortar, I plan to use that from Limebase, which I think looks to contain a pozzolanic additive to speed the cure, though it doesn't actually say in the blurb, I assume that's what the additive is as well as aggregate?

https://www.limebase.co.uk/lime-mortars/ham-stone-fine-building-pointing-lime-putty-mortar

Thanks again for the link! I had mental images of me spending ages using a large builders protractor in the rain....

 

[Bullet-Proof_Biscuit]

Yeees.....

 

[stuart45]

Limebase are really good. Ask for Joe, he will give you plenty of help.
These are the old way of getting the circles. Plus a length of 2x1.
Workshop Heaven Trammel Heads