16c Fireplace - delicate renovation

[surreysteve]

Hi Guys

Am about to undertake renovation of an old open fireplace with a very large , fragile and shallow arch. It had been concreted over since the 1960s (Yes concrete). It is around 6-7ft wide. The bricks are small, very old and held together by crumbling lime mortar.

I have been removing the concrete with a view to completely repointing the brick work (section by section) - but came to a point where I realised the entire arch may come down if I wasn't very careful.

To avoid this (and to provide strength in future), I had a wrought iron support made to sit underneath (close to the) the bricks and be fastened to the vertical pillars each side. The arch is now fitted and has a fairly smooth arc leaving some gaps between it and the rather more uneven brickwork.

My intention is to fill the gaps to provide consistent support for the bricks along the entire horizontal length. This leads to my question:

What should I use to fill the gap between the metal support and the bricks. This would need to:

1. Bond to the old bricks and the wrought iron
2. Be strong and solid to provide support for bricks above
3. Have some degree of flexibility to deal with any slight movements and expansions that may occur (This will be working fireplace)

I have posted some pictures as a picture paints a 1000 words they say!

All help and advice welcomed!

Steve

 

[livias]

Well done, that should stop it falling down.

I would use lime mortar. To be aesthetic it should be a similar colour and texture of mix to that around it ... though a bit of soot works wonders ... If the original is crumbly then I expect that it was lime putty mortar.

The only issue that I can foresee is that you don't want to be lighting fires underneath it until it has a reasonable set, so you need warmth (I expect it is OK as it is indoors) moisture (damp the bricks down well beforehand and keep a spray of water handy) and plenty of CO2 (which is the main concern in that location so nearby set an electric fan going to get the air moving)

Anna

 

[Zebra]

There is quite a lot of distortion in the brickwork on the right hand side of the fireplace, isn't there? Do you think that the arch and the brickwork above it are of the same age? I can't think that the brickwork would have been built like that.
It may have held fine without the wrought iron arch, if you had made a temporary former to support the brickwork in its current position while you repointed. The wrought iron arch isn't too bad though.
As for filling gaps, you could use the same mortar as you use to repoint. If the gaps are too large, get a piece of clay roofing tile, wedge it in the gap as if it were a tiny brick, and point around it. Repairs of this type have been made in my 17th/18th century brick walls, both in earlier periods, and by me.
What mix are you planning on using for your mortar? The brickwork looks very old, so if it were me I'd use one made with lime putty, and a mix of soft and sharp sand. What am I saying though! Don't get us all started on lime mortar mixes. We'll be here all week!

 

[Flyfisher]

It's difficult to see without a full-frontal picture (oo-er), but there doesn't seem to be much of a supporting arch at all really, given the width of the almost horizontal middle section. Is there any sign of some sort of centre support in the past?

I'm sure the new ironwork will help, but the horizontal-looking middle section also doesn't look like it's having much of an arch effect. It looks as if the ironwork could be fairly easily pushed down if that central acroprop wasn't in place . . . . but perhaps it's just the angles of the photos?

Perhaps the 'arch' is only supporting the weight of the few courses of bricks above it and not the entire ceiling/floor above - depending on how the rest of the stack is built anyway?

As for filling the gap between the iron and brick work, when our inglenook bressumer was replaced, I packed the gap with slate to ensure no shrinkage of gap-filling mortar, but this was an invisible bit of work because the wall was then plastered over anyway. In this case I'm assuming the wall will not be plastered so packing with slate would not look very good , in which case I'd agree with Zebra's suggestion.

 

[billybuntus]

Tricky one that. I can see it was obviously made by someone who didn't believe in gravity.

Looks like the cast iron strap should keep it together. You've be surprised at the strength of even the weakest of lime bonds. I recently cut a foot out of the bottom of a lime and brick bay window of which the brick was completely saturated and had de-laminated extensively and it held over a 2 meter span. Pretty impressive.

Whats the depth of the wooden beam? Looking at it I would hope that is taking the weight of the floor above and the arch is not.

I'm not entirely sure that the brickwork has moved much. Looking at the arc of bricks in the center of the bay if there had been that much movement the whole thing would have fallen down. Perhaps a very unskilled 'bricky' laid it and just did the best he could then lime rendered over it.

Other than what you've done which looks find I'm still unsure how I'd of tackled it. My first thought was to build an internal archway and leave the original exposed set back around a foot.

Can you take a picture under the arch to see whats up there? Just curious

 

[billybuntus]

I'm sure the new ironwork will help, but the horizontal-looking middle section also doesn't look like it's having much of an arch effect. It looks as if the ironwork could be fairly easily pushed down if that central acroprop wasn't in place . . . . but perhaps it's just the angles of the photos?

Perhaps the 'arch' is only supporting the weight of the few courses of bricks above it and not the entire ceiling/floor above - depending on how the rest of the stack is built anyway?

The ironwork will certainly help though and prevent it collapsing. You'll certainly see movement in the ironwork before a collapse.

I agree. I can't see how it would support any weight above it.

 

[88v8]

That's quite an arch. Amazing it's stayed up all these years.
It should have been built on a support, as ours below, so the bricks sit direct on the wrought iron. Which, incidentally, is about 3" x half.
Putting the support in retrospectively is difficult.

AFAIK there is nothing that will bond to the iron and the brick, other than resin perhaps, and when you light the fire the differential expansion of the iron and brick would pull the face off the brick. So, I don't believe you can actually glue them together.

Depending how strong your iron is, I would wedge it from the back with slate or tile, and lead, then try to run a mortar fillet along the front. All very fiddly, and I suspect the end result may have an air of rusticity about it. Which is not necessarily a bad thing.

Ivor

PS irritatingly, Bucket has cropped the rh of the pic... the support extends about 9" into the rh stonework, and about the same on the left, where it has been partly pointed over.

 

[Keith Bowman]

I am not an engineer, but I have to point out that the new piece of iron is not cast iron nor is it likely to be wrought iron (ie pure iron with no added carbon). It looks to me like plain ordinary mild steel flat bar about 1/4" thick. I cannot see how it can carry any serious weight at all in that configuration, but perhaps the picture is misleading. Sorry to be a Jeremiah - but do please stand well back when you take the Acro props away.

 

[88v8]

I am not an engineer, but I have to point out that the new piece of iron is not cast iron nor is it likely to be wrought iron (ie pure iron with no added carbon). It looks to me like plain ordinary mild steel flat bar about 1/4" thick. I cannot see how it can carry any serious weight at all in that configuration, but perhaps the picture is misleading. Sorry to be a Jeremiah - but do please stand well back when you take the Acro props away.

Jeremiahs can serve the very useful function of saying the unsayable.

The arch is carrying, as far as I can see, about 60 bricks of single-thickness wall, in a triangle with a base of 10 bricks? If each weighs 4lb, that's around 240lb** distributed. So, in a sense, not that heavy. However, have to agree that a strip of mild steel will not do much more than stabilise it, but does serve as a demonstration that something more may be needed.
** edit - forgot the mortar - make that 280lb.

Also, because the arch is three-centred it's not really possible to build in the ends as was done with the arch in my pic.

Really, that strip needs to have an upstand - like a piece of angle iron - welded to it so as to make a T shape. Then it will carry a load. The way to do that is to make a ply former which traces the shape of the arch, then take that it to a blacksmith and have him make a T support to the exact profile. That will have the strength and need minimal infilling. A smithed iron support will be stronger than one made of mild steel.
He could also make more elegant splayed ends, so it doesn't look like.... a strip of mild steel.

I do mean a blacksmith, not just a chap with a MIG.
Like this
http://www.peterneale.co.uk/whatwedo.html

Having obtained your iron support, you could then sit it underneath, or, better, carefully remove a few bricks above the arch and support the wall with putlogs and acrows, then remove the bottom course of the arch and rebuild it on the iron support.

I'd think carefully about the paint finish, if any. Might be better with graphite paste and no paint at all.

It could end up costing £££, but it will be pretty special when it's all done.

Ivor

PS useful to edit your Profile to show your location

 

[surreysteve]

Hi Guys

Thanks for replies so far, very helpful.

So far I am taking that Lime mortar would be the best 'filler' and that packing with slate/tiles might help. I also understand I probably have a mild steel strip not wrought iron (Apologies my ignorance). I have already purchased ready mixed lime mortar from Mike Wye (In West country) and will knock up well before use and also make sure everything is kept damp before , during and after the work. I will leave the filling for a week or so to gain strength before doing any repointing.

NB The strip is a little more substantial than people may think, being about 8mm thick x 8cm wide. It flexes a little but not too much and feels quite solid.

I have also taken some pictures (3) behind the arch as requested. This may help to explain why the arch has stayed up for so long as there is a good layer of mortar/concrete on the back. I'm guessing this was done in the 60's when then previous occupants rendered all the fireplace brickwork with concrete/mortar. This was all part of a horrendous 60's facelift for the (Medieval!) cottage which included painting all the beams white and adding in a skin of plasterboard to all external walls (Covering up original beams/lime panels). Sacrilege I know!

I have also updated my location as requested.

Any further tips/comments welcomed as I intend to start work next week.

Cheers

Steve

PS Apologies for lack of picture - I am getting message "Sorry, the board attachment quota has been reached." . Don't know how to get round this - suggestions?

 

[88v8]

Photobucket or the like. Copy/paste the img code.

Ivor

 

[surreysteve]

I think this link should work to the album of images on Google Plus

https://plus.google.com/photos/+SteveTeague/albums/6071881638700370913?authkey=CKCT3_yK27-BBA

 

[billybuntus]

That strap should be fine its a monster

Not that you ever will but if you tried to pull the archway down I bet you'd be surprised at just how strong it is. That strap will ensure things are nicely braced.

 

[c r]

Hi Steve

Look to source a well graded sharp sand (or grit sand as is sometimes called), roughly speaking this would have range of particles right upto 5 or 6mm size. Wet the brickwork well beforehand, several times. Rather than making an overly wet, sloppy mortar mix, its best to pack and tamp in a pretty 'dry' mix, and then spray the setting mortar over next few days, from time to time. I don't know what tools you have, but it may work best to apply mortar with whatever small metal type of trowel you have and then bash and compress in it in further using small offcuts of wood. The day after applying mortar you should firm it up by again compressing it with a bit of wood or a stiff trowel, as even with a dry mix there will likely be some slight shrinkage as mortar sets.

Remember that the putty will have a fair amount of water content in it already so you shouldn't need to add much water to the putty&sand when mixing up the mortar.

*edit- sorry i misread your later addition, so your mortar is ready mixed, in which case when you open the tub, it'd be good to pour off any water at top of tub, then lay out the mortar on a board, or plastic sheet, to allow a bit more water to drain away, so your mix will become less wet. You could even do this the night before you plan to do the work, if you cover the mortar with more sheeting. Don't worry about the lime setting whilst you do this, it will still be usable next day. Sorry hope that all makes sense, good luck

 

[agbagb]

Hi Steve,

As far as can tell from the photos, the floor above centre beam (probably had a proper name) is sitting right over the centre of the arch and is well below any self corbeling of the brick work. The arch has shifted in the past hence the dip in the brick courses over the arch. The beam has been propped and packed back up.

The original arch curve would have been steeper but still not enough for for the sides of the fireplace to resit the outward thrust (spread). Just a slight movement of these will cause a large deflection of the arch. The steel as it is will only add a little resistance to this spread and potentially not enough. Expansion of this length of steel might even cause more spread when your stove is blasting heat out. (2m @ +50 degrees = 1.2mm)
This might help explain.

Do I see an angled timber going from the outside of the fireplace to the beam that the centre beam is resting on? Is there one on the other side? If so could this (these) have been added after the previous collapse to restrain spread of the walls? (think, like an upside down flying buttress).

If at all possible I would consider tie bar(s) at the back of the arch going all the way through the side wall and tightening up. If insulated they would keep the tension and restrain the spread. You could cast concrete around them (think, like a concrete lintel) this would also hold up the arch bricks without the visible bar.

I think you've got a good historical example of a design that didn't work. It'll be great if you can preserve it whilst keeping it safe.

I can see by the stack of loo rolls, you are well prepared for all eventualities.

Andy

 

[plasticpigeon]

Wow the way the arch has dropped is a bit mad. How about some beefy cantilever or bracket off the wall behind the stove to hold the middle up with minimal visual impact.

 

[Keithj]

Looking at the angle of some of the brick courses in the top photo, I would be worried about what had happened in the past and what repairs had been carried out.

I don't think that steel strap will hold for long if the bricks decide to let go. I'd be inclined to get a suitable expert structural engineer to have a look - maybe with your CO in attendance at the same time, if you're listed.

 

[TheRoost]

If you are sticking with your original steel strap I would at least secure it with some more anchor bolts - you have two per side and they are quite low down on the vertical pillars at the ends of the strap - if the strap ends up taking some weight it would droop in the centre as the strap pulls away from the pillars at the bends - I would add another anchor bolt through the vertical pillars, high as you can just before the bend starts, to give a little bit of tension.

 

[surreysteve]

Thanks for all the advice so far.

I have packed out the space between the supporting strap and the fireplace with pieces of slate and started to prepare the brickwork for re-pointing.

In doing this it became apparent that it may be better to remove the remaining concrete covering the front of the bricks before the delicate re-pointing. This was achieved over a couple of hours with a combination of careful chiselling and the use of a small angle grinder to weaken the surface of the concrete.

The good news was that it didn't fall down and a new picture has been added to my album

https://plus.google.com/photos/113145483048013937439/albums/6071881638700370913?authkey=CKCT3_yK27-BBA

I am now unsure what to do with the "gap" above the brickwork.

The chimney is 16c and I am aware that adding in old bricks (I have some) would not be considered good "Conservation". It would also add to the weight on the arch. Repacking with slates/concrete also seems a poor way forward.

One idea I had was to add a horizontal wooden "cover" made of 3-4" of oak that would run across the width and cover the unsightly gap in the fireplace - this could be new oak and therefore also a good conservation approach? It would also not add weight.

I imagine we have a good audience of keen renovators AND conservationists - what do you think?

All ideas welcomed

Steve

 

[88v8]

Bloomin eck, that really has sagged.
Regardless of 'conservation traceability' - which tbh I regard as mostly bo***x - I think you are very right to be wary of adding any weight.
An oak cover strip of some form seems a better option.

I still think you should insert a proper wrought-iron support and rebuild the arch on it.

And those pozis(?) fastening the steel strip to the brickwork don't look inspiring. A couple of 4x½” coach screws in big plugs would give a little more confidence. Although not very much.
If that arch were in the room, would you be happy sleeping under it?

Ivor