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00:01Britain's history is recorded in its monuments.
00:05Even before the Normans came and built their castles across the country,
00:08successive generations have left their mark on the landscape,
00:12in the landmarks they've left behind.
00:15But now those landmarks are crumbling.
00:18You can see there's a section there which is quite bad.
00:20Centuries of wear and tear have taken their toll on these precious buildings.
00:24More of the structural members were suffering from corrosion than we expected.
00:28There's moss growing inside, so then the water backs up, then falls internally.
00:33They need constant care and maintenance in all kinds of conditions.
00:39You can see dust coming up, 100 years old dust.
00:42Revealing treasures that have been hidden for centuries.
00:45We're unearthing the original bridge.
00:47All over the country, teams of highly skilled people are dedicating their lives to keeping our heritage standing.
00:54We need to be aware that we are part of a cycle that's been going on for centuries.
00:59These are Britain's landmark fixers, and this is not just their story.
01:04They took nearly 6,000 holes to drill.
01:07How marvellous.
01:08But the story of the buildings they look after.
01:23Edinburgh, jewel of Scotland.
01:25This ancient royal city is steeped in history, but it is also the birthplace of our modern world.
01:37And spanning the gap between old and new, stands a bridge that, in its day, was a wonder of new technology.
01:44Edinburgh North Bridge.
01:47This bridge was truly ground-breaking.
01:50The materials that they used and the way that they used them was revolutionary for its time.
01:55This is when Victorians thought they could do anything.
01:58They didn't even blink when it came to the question of spanning a 160-metre gap using new materials and new technologies.
02:08Built to span the divide between the medieval old town and the burgeoning new town in the north, this bridge is the artery for the beating heart of the city.
02:18It's one of the key north-south connection points through the city.
02:21Thousands of people and vehicles cross this bridge every day.
02:25Back in the day, those would have been horse and carts, but now there's 40-ton vehicles which are travelling along North Bridge each day.
02:31But now this marvel of Victorian engineering is showing its age.
02:37Pretty quickly we realised that maybe the bridge was in worse condition than we had hoped.
02:41Saving the bridge and restoring it to its original grandeur will be a mammoth undertaking.
02:47We generally have about 100 skilled operatives working for 12 days' schedule, 12 days on, 2 days off.
02:54So that includes the cast iron facade restoration, the structural steel work repairs.
02:59It's dirty, it's dusty, you have to work in a very harsh environment.
03:04The deck shouldn't spray concrete.
03:07It's very powerful, and in the wrong hands it's hateful.
03:10There's also the grit blasting and painting of the entire structure.
03:13And all of this while keeping the bridge open to the general public.
03:18We're directly above Waverley Station, which must remain open at all times.
03:21We've got 25,000 volt overhead lines and live trains below.
03:25North Bridge itself, which must remain open to traffic and pedestrians alike.
03:30So it's a rather complex challenge.
03:36It's 5pm and whilst commuters and tourists pour across Edinburgh North Bridge,
03:42on the southern end, in the basement of a former department store,
03:46Stephen Knox and Billy Long are about to step back in time.
03:51The scaffolders have been in and made a safe for Stephen.
03:54Please watch your step when you come down through.
03:57I'm really looking forward to seeing these.
04:03There's not been anybody in here for quite a while.
04:05Billy is part of the team carrying out a full inspection of the North Bridge.
04:10He's been tasked with investigating the structural integrity of the approach to the bridge.
04:16Pretty special.
04:18And after months of piecing together clues,
04:20he's discovered a long forgotten chamber that reveals the foundations
04:25where the bridge joins up with the roads of the old town.
04:28This is really incredible, Billy.
04:30I mean, we knew about these, but how did you actually find them?
04:33We went through all the Edinburgh City Council archives.
04:36We went through all the old drawings.
04:38We found all the old correspondence.
04:40And we kind of pieced it together.
04:42We figured out how to get access down through speaking to the maintenance manager.
04:45Just putting together the backstory of the structure,
04:48the timeline of where we were then and where we are now.
04:53These stone foundations were thought to be buried underneath the expanding city.
04:58So this is us under the footpath at the moment, Billy,
05:01just on the approach to the bridge.
05:03It is. The footpath is directly above us.
05:05That's the old arches under the road.
05:07It's really fantastic, Billy.
05:08We're essentially unearthing the original bridge.
05:13Stephen and Billy have discovered the original stone archways
05:16that carried the road onto the first north bridge that was built in the 1760s.
05:23That's the east side of the old bridge.
05:25The north bridge is in remarkable condition.
05:30And that bridge was built for a very specific purpose.
05:34Edinburgh was one of the most dynamic, progressive, enlightened places in Britain.
05:40But it didn't look it.
05:42It looked like something from the medieval past.
05:46The city was actually restricted to the very dramatic, stunning castle
05:51that sat on top of an alert volcano and then the ridge that ran eastwards.
05:56And what this meant was that 35,000 people lived in under a mile of space.
06:02So it was very built up, very smelly.
06:05And at the time, it was one of the most densely populated areas in the world.
06:11Something had to be done.
06:14In order to allow Edinburgh to breathe, the city decided to build a brand-new,
06:19Georgian, beautiful city north of where Edinburgh Castle stood.
06:24And the new town is going to be planned, it's going to be spacious, it's going to be well-structured,
06:34and it's going to be all the things that the old town isn't.
06:38What they wanted to do was to open up some of the land to the north of Edinburgh,
06:43and they needed to do that.
06:44They needed to expand the Noor Lock, which was in the valley here.
06:48The old Noor Lock was originally part of Edinburgh Castle's defences.
06:52It's this man-made pit of stagnant water, effectively, acting a bit like a moat for the castle.
06:59And what needs to happen is that needs to be drained to be dealt with,
07:04but also you need to find a high-level connection to the nearest high ground.
07:08There needs to be a bridge.
07:10So in 1765, they built one.
07:13It basically spanned the entire 1,100-foot gap between the old town and the new town,
07:20with three huge arches and then a load of little arches in the piers from side to side.
07:26It was an enormous engineering project.
07:29These side arches, embedded into the foundations of the old town,
07:34are what Billy and Stephen are exploring.
07:37That's the original stonework.
07:39There's been some brick infill at a later date by the looks of it.
07:43It gets more impressive when the further down you go.
07:46Through here, you can see an even bigger arch.
07:48The stone arch has been a successful bridge design for over 3,000 years.
07:55Instead of pushing straight down, the load of a bridge's arch is carried outward along the curve of the arch,
08:01to the support at each end.
08:03Billy and Stephen need to check these arches are still structurally sound enough to support the road above them.
08:14Billy is looking for a point where the old bridge collapsed, shortly after it was built.
08:19It was in use, and the cracks were noticed.
08:22The designers were called in, I believe, at the time, according to the history books.
08:26And they chose to ignore it at the time.
08:29In August 1769, it actually collapsed.
08:32Architecture and engineering is really about a constant fight against gravity.
08:40In order to ensure the stability of a structure like a bridge,
08:45you have to be able to support it through solid foundations.
08:49Those foundations are what gives it its strength in many respects.
08:54And what they're doing is they're taking all the forces and the weight
08:57of the structure above them and channeling it into the ground.
09:01The problem with the foundations of the North Bridge is that as people have developed and built in the old town,
09:07they have thrown the soil from their sites against the face of the crag.
09:14It's not compacted. It's not solid.
09:17Unfortunately, because the south end of the bridge had been built on this rubbish, loose material,
09:23it led to the side walls of that end of the bridge collapsing.
09:27And five people that were crossing at the time died.
09:32These are the old buttressing, strengthening details that have been put in towards the end of the project
09:37after the whole south span collapsed.
09:39Despite its age, the stone footings are in remarkably good condition.
09:44It looks structurally so. I've not seen any sort of significant cracks.
09:48This bridge was built for horse and cart.
09:50And now we have modern cars and glories travelling over the top of this
09:54with, to be honest, very minimal signs of distress.
09:57How they accomplish this?
09:59Yeah, beggars belief in terms of the skills that went into these arches and this bridge.
10:05To me, it's as good as they knew it was built.
10:08That's really interesting, Billy. Will we head back?
10:11Yeah, truly a special.
10:13It's been a worthwhile investigation.
10:16The load-bearing arches are all structurally sound and the approach roads to the bridge are secure.
10:27Back on the street level, Stephen can give the go-ahead for the refurbishment of the bridge.
10:32Full access to this structure hasn't been gained in over 70 years.
10:36It was the first time that we were able to get up close and personal with the entire structure.
10:41The bridge they are working on is not the old stone bridge.
10:45It's a Victorian replacement, built in 1897.
10:49And it was built for a very particular reason.
10:53The new north bridge has to take account of the fact that into that valley has arrived a station.
11:00It is a station that is going to become the second busiest in the whole of the United Kingdom.
11:06And the old north bridge prevents that from happening.
11:11The narrow stone arches of the old bridge limited the number of train lines that could be run into Waverley Station.
11:19And so the bridge design had to be transformed.
11:22This wasn't possible with stone.
11:25Stone arches have a natural limitation on them.
11:30There is a certain point at which if you keep adding, keep trying to span wider, the stone will fall apart.
11:37But the Victorians had a revolutionary new solution.
11:41The Victorians had this new wonder material and that was steel.
11:45The strength of steel, the tensile qualities of steel and the relative lightness of steel enable you to span far, far bigger distances than stone ever can.
11:59The refurbishment team led by Rory McFadden are in awe of the Victorian workmen who built this bridge.
12:06When we look back and think about how the guys constructed this in the day, they had very little of the equipment that we have nowadays.
12:14There's thousands of rivets that all had to be installed by hand, heavy steel work that had to be moved by manual means.
12:20So it would have been a really impressive feat seeing it being constructed.
12:23In its day, Northbridge was a wonder of modern engineering, but today it's an urgent need of repairs.
12:32We've identified some issues with the external columns.
12:39A lot of the existing steel work has corroded, so it's a lot thinner than it used to be and therefore it doesn't have the strength.
12:46Pretty quickly we realised that maybe the bridge was in worse condition than we had hoped.
12:50Edinburgh Northbridge is rusting with age.
12:53Edinburgh Northbridge is undergoing a multi-million pound refurbishment to bring this 120-year-old vital link between old and new Edinburgh back to its former glory.
13:16But before any work can take place, the entire bridge needs to be encased in scaffolding.
13:28Glen Henderson is the temporary works coordinator for this project.
13:32He coordinates the scaffolding works on site.
13:35The main scaffold assembly at its peak might have had as many as 60 scaffolders building it.
13:41And the design of the scaffolding is unique.
13:44One of the key complexities of the scaffold was that we don't have the ability to be able to support it from the ground.
13:49So everything must be suspended from the structure itself.
13:53The complex scaffolding hangs below the bridge and supports a working platform 23 metres wide and 170 metres long.
14:02It's a vital safety feature for the team working 21 metres above running trains and 25,000 volt overhead lines.
14:15You can see that all of the scaffolding obviously made of metal relatively close to the overhead lines.
14:21So all of that metal work had to be electrically bonded back onto the railway.
14:25But the deck is also there to protect the station below.
14:29When we planned the project, we understood that we had to protect Waverley Station's roof, which is incredibly fragile.
14:36It's immediately below our works.
14:40Edinburgh Waverley is a historic monument in its own right.
14:44This great glass roof is the size of 14 football pitches, but you do not want to drop your tools through that glass roof onto the head of some unsuspecting passenger.
14:59Immediately below that roof is a live open station, so we must protect that all the time.
15:05So we've actually installed a protective corrugated treating system that you see here that's been impact tested for scaffold tubes to be dropping.
15:12So everything we've got here is protecting the glass and the roof immediately below us.
15:17In total, 13,000 boards, 75,000 scaffolding couplers and 300 kilometres of scaffold tubes have been assembled onto the structure that hangs below the bridge.
15:34The project isn't a scaffolding project. The project is a restoration project of the bridge.
15:39The scaffolds here to facilitate those works.
15:42As a result, the scaffolding is constantly changing with the project.
15:47We built the access scaffold to allow the design engineers access to then assess the structure.
15:53We're learning more about it now that we have the access, and we have to modify the scaffold to install some of the repairs.
16:01Engineers have identified an area that needs to be strengthened.
16:06An additional beam needs to be added.
16:08The scaffolding team have to break a hole in the deck and climb down to install it.
16:15OK, chaps.
16:18So, we're going to have a ground man downstairs just to make sure that nobody's walking below us when we're working at height.
16:24And we'll start lifting the boards out.
16:25Having erected a temporary handrail around the danger zone, the boards are lifted to reveal the underside of the scaffolding.
16:34The team suits up to step into the void.
16:37There's obviously the potential that the guys could fall from height.
16:40That's why it's essential that they wear a harness, and that they're connected onto this device.
16:46In the event that they were to fall, it would stop them.
16:48The chaps have loaded themselves down onto the scaffold droppers, and they're going to be lifting a new scaffold beam into position.
17:01The new beam is lifted into place, and the scaffold is adjusted to take the new load.
17:14So, essentially, what we're doing here is we're installing bracing to restrain the bottom of the beam.
17:18Do you want to climb over it first?
17:21The new scaffold is braced and ready to do its job.
17:25So, that's the lads finished the job now.
17:27Let's go upstairs.
17:28We can modify the support arrangement and watch these guys move on in the job.
17:36Whilst the protection deck is in place, the refurbishment team can begin to peel back the layers of the bridge to reveal and restore any damage.
17:48Beginning with the cast-iron features that adorn it.
17:54The bridge itself is made of structural steel, but that's enveloped then in cast iron.
17:59The cast iron was used because you could form real decorative features.
18:03So, you have to put yourself in a Victorian mindset when you're thinking about the North Bridge
18:08and how you want to decorate your new engineering project, because the Victorians saw themselves as the new Rome.
18:14They wanted to emulate the Romans, the Greeks, all of their beautiful sculpture, and they could do that using new material.
18:23Cast iron was widely used by the Victorians.
18:27They could mould it to shapes and patterns to decorate many of the buildings that they were constructing.
18:32What they would do is create a pattern in wood, and they would then use that to make a mould in sand, and then they would pour molten cast iron into this mould of sand.
18:43And then when it hardens, you take it out of the sand, and you do that again and again and again.
18:50And this means you've got mass production of huge amounts of decorative material.
18:56You can use it to make your engineering work look delicate, look intricate, and look almost organic.
19:01Not only did it make it a decorative structure and really impressive looking, it also provided weather protection to the steel work that's in underneath the bridge.
19:11The decorations on the bridge are like an enormous jigsaw that has to be taken apart, repaired, and then reassembled.
19:19Bruce Wade is the engineer whose job is to assess the catalogue of all the cast iron pieces.
19:28On each elevation, there's 206 components, so 412 per span, and there's three spans, so there's just over 1200 cast iron components that have to come off the bridge and be catalogued.
19:41Bruce has labelled this section of the bridge so that the components can be removed.
19:45So you know exactly where to go when you're putting this bit back.
19:49Removing the section is not an easy job.
19:52It's suspended above a void, so the guys have to be strapped into safety harnesses.
19:58And the facade is held in place by two steel cleats attached to the bridge columns.
20:03These have to be hammered loose before the 320 kilo section can be lifted out, using a block and tackle.
20:09And the scaffolding is constantly getting in the way.
20:19And Bruce doesn't just have the arch sections to worry about.
20:31Each span elevation is lined with floral decorations painted to look like stone.
20:49So this is a decorative floral component, one of ten on each elevation.
20:54So what they'll do with this is remove this and use the merlot to crane it out onto the road.
21:00From there it'll either go down to a repair shop to be repaired depending on the damage.
21:06So although this looks quite fragile and light, it's actually around 60 kilograms to lift out itself.
21:11The crew assigned to do this is led by their foreman, Tommy.
21:18So what are you going to do today, Tommy?
21:20We took the fruits and flowers architectural piece off.
21:23We're going to take along here and we're going to lift out onto the traffic management area.
21:28Tommy heads up top to get the merlot crane into position.
21:33It's challenging with other people here.
21:36First of all, we've got the life traffic running.
21:37What we'll do, we'll barrier it off so people can come in the lift area.
21:42For such a small little lift, it sometimes can be tricky.
21:46Tommy's going to have his work cut out to get this done in time.
21:58On Edinburgh North Bridge, the team are preparing to lift a piece of ironwork from the deck below.
22:03The merlot crane is manoeuvred into position.
22:07Its legs are stabilised by footing plates.
22:10And Tommy makes sure that the marshals are in position, ready for the lift.
22:15Well, I need two people up here.
22:19Greg's up here, but I still need his finger up here anyway.
22:22I'm going to go down there and coordinate this lift now.
22:23This is just one of the 1200 lifts that Tommy will oversee before all the cast iron pieces are restored and replaced.
22:32The scaffolders are ready in place.
22:35They will guide the crane's wire down to the lift.
22:39And make sure that the cast iron lifts out safely.
22:42Well, the lads did it professionally. They've got it out all safely, so job well done.
23:03What will happen now will get transported through a safe area off-site, ready for inspection.
23:10Any damaged pieces will have to be repaired before they can be reinstated on the bridge.
23:15But fixing cast iron on an industrial scale is no easy job.
23:29The renovation of Edinburgh Northbridge is finally revealing the girders that form the structural skeleton of the 53-metre-long arches.
23:37My colleague Graham, he's removing the steel plates just now so that we can actually see the condition of the bridge down below.
23:46This allows the engineers to do a further assessment on the condition of the bridge.
23:53The bridge's three arches are built with 1,966 tonnes of steel, a relatively new material for Victorian engineering.
24:01Before the 1850s, steel was a very expensive material because it was difficult to produce.
24:08The problem has been that the energy required in order to turn iron into steel just hasn't been present.
24:17But in 1856, a British industrialist, Henry Bessemer, invents a process whereby blowing air through molten metal could remove the impurities.
24:27And this reduced the cost of producing steel.
24:31His new process meant that he brought down the cost of making steel by six times.
24:36And for the first time, steel became a material that you could mass produce at a low cost.
24:42So you could build much taller, so we saw bigger structures than we'd ever seen before.
24:46And it also meant that you could create bridges that could span longer than they could before.
24:50Edinburgh North Bridge was able to span the 171 metre wide valley over Waverley Station, with 6,300 girders held together with rivets.
25:03But steel, while incredibly strong, is also susceptible to rusting.
25:09And the refurbishment team has discovered that the steel work is in far worse repair than they expected.
25:14So the type of defect that we found in this area was that sections of the bridge that were exposed to water ingress, a lot of the existing steel work has corroded.
25:26Rory's team needs to identify how many of the girders need repairs and fix them.
25:32To do that, thousands of steel rivets holding the girders in place need to be removed.
25:37And that's easier said than done.
25:40Make a noise, eh!
25:42Make a noise!
25:44No, no, no!
25:47Make a noise!
25:51We've got a team going in advance, surveying all the repairs.
25:54We've got the designers back in the office providing some design input.
25:58And then, ultimately, the guys come back then and actually execute the repairs.
26:02It's cramped hard work, but the team aren't fazed by it.
26:05It's not too difficult. It's only held them back up the rivets.
26:14Put that hammer!
26:16The task of assessing the structural integrity of the bridge falls on the shoulders of engineer David Bishop.
26:25How they managed to construct with very tight tolerances without the craneage and the access scaffolding that we have today is quite incredible.
26:34And it must have been a feat of engineering achievement.
26:36David oversees a sophisticated 3D computer model, which can render all aspects of the bridge in minute detail.
26:45It's created from a high-tech laser scan of the entire bridge.
26:52Once built, the model allows David and the designers to plan the works on the bridge down to less than a millimetre in detail.
26:59This particular area shows the cast iron facade. If I hide this section, it will show the wire frame.
27:07I could then progressively move through the structure, identifying the strengthening elements, the bracing members that are under construction.
27:13When you extend over the bridge, you can see all three spans. Every location is different. Over time, the corrosion has been different.
27:22So it's very bespoke strengthening that we require in every location.
27:25On the 3D team's recommendation, custom-made steel plates are added to the Victorian girders to strengthen the structure.
27:34On the face of it, the job is pretty simple.
27:47I'm just speeding that boat through for this side here, just to hold down that position for us.
27:50But in the cramped confines of the deck, nothing is simple.
27:55It's got its challenges. You're trying to lift stuff in, and you might clash with scaffold, you might clash with existing steel that's already there.
28:02But we'll get there in the end. That is difficult. If we had all the space in the world, you'd probably fire these in quite quickly, but it takes its time.
28:10It's always hard to get the first one lined up. Once you get that lined up, it's quite straightforward after that.
28:24Strengthening the bridge's girders is a relatively straightforward process.
28:36But repairing the ornate cast iron work that decorates the bridge requires a rare set of skills.
28:42And Peter Palmer's family business has them.
28:48The company was founded in 1946 by my grandfather. He developed the process of welding cast iron as we are today.
28:56The process hasn't really changed since 1946.
28:59Peter's team have to assess each individual piece from the bridge and weld any cracks back together to reinforce its structural integrity.
29:09Everything can be salvaged. It's just a matter of having a look and understanding the requirements and the damage, what we can do to it.
29:17But welding cast iron is a delicate job, because cast iron is surprisingly fragile.
29:26When you pull iron, it goes quite crystalline. And so that means if you just tap it, it could break.
29:31And that also means that you can't solder it to repair it very easily either, because it hasn't had all that working.
29:37I like to think of cast iron a bit like Italian biscotti, where if you try and bend them, they just snap or break.
29:43And that's similar to cast iron being really brittle, so if you drop it, it's very prone to breaking.
29:49It's very brittle, especially sections off the north bridge, because they're quite thin.
29:54So we basically treat them like sheets of glass.
29:58Like glass, if you work with cast iron cold, it will break.
30:03So the team has to heat each section to 600 degrees by building a brick kiln, known as a muffle, around it.
30:11Mark the welder covers the kiln with a fire blanket of alpaca wool from Mexico, that can withstand temperatures up to 1200 degrees.
30:20This keeps the temperature in, but also gives us easy access to the repair area.
30:26It's crucial that they heat the cast iron at a slowly rising temperature of 100 degrees per hour.
30:32Any quicker and the casting will crack because it's cast iron and it's so brittle.
30:37So we're going to raise the temperature slowly overnight.
30:41So that's it now. That's nothing more we can do today.
30:44That's a waiting game until the morning.
30:46It's 7am. Mark arrives at the foundry to check on the piece he's been heating overnight.
31:01He's joined by Peter, doing his morning rounds.
31:06Morning. Is it up to temperature? Not far away.
31:11Yeah, we're at 590. We're ready to start. Lovely. That's great.
31:16To repair the piece, Mark has to melt a cast iron filler rod into any cracks using an oxy-acetylene torch.
31:26The tip of the welding torch, the cone, is around 3000 degrees.
31:32There is no room for error.
31:34It's a very high level concentration as you have to manually check the molten pool for any defects.
31:42And Mark is doing this while bent over a fire blanket above a searing heat of 600 degrees.
31:49You also have to keep maintaining the temperature of the casting.
31:53Because if that keeps increasing then it will go beyond the 600 and cause searing distortion.
32:04That's it. Completed. Finished.
32:09Once that's cooled down over the period of time, if you actually put that under the microscope,
32:14the only slight difference is it's actually stronger than the original casting.
32:19The cast iron piece now has to undergo a quality control check.
32:24So if we can do the dye penetrant test on all the welded areas and make sure they're OK.
32:30The piece is painted with a red dye that soaks into any defects in the metal.
32:35When a white developer is sprayed over the top,
32:39any cracks in the metal will show up as a red line.
32:42It's a tense moment.
32:45If there is any cracks, it is back to square one, back to the welding.
32:49No red marks or no defects or cracks there, so we're happy with that.
32:54All that remains is for the section to be repainted with red oxide primer to protect against rusting during transport.
33:03Then it's back to Edinburgh for the final stage of the bridge refurbishment.
33:07Come down easy.
33:08At the refurbishment of Edinburgh Northbridge, project manager Rory McFadden is wrestling with another problem.
33:25You might not realise it, but below our feet, there's quite a few guys in working on the actual concrete deck itself.
33:33The deck is the hidden substructure that supports the road above.
33:37The public only see a thin layer of tarmac on top, but below that is a thick layer of reinforced concrete.
33:43So concrete is at least as old as ancient Rome, and in fact it's older than that.
33:51I mean, there are examples of concrete structures going back centuries, millennia, before the Romans used it.
33:59So it's not a new idea, but it's an idea that revives and gains a new kind of energy in the late 18th century.
34:07So there's this French gardener, a guy called Joseph Monnier, who basically was trying to make bigger pots,
34:13and his pots kept cracking because of the frost, and they kept cracking because of the size of the earth that he was trying to put into them.
34:19And so what he did was he reinforced his pots with wire.
34:23And of course this meant other engineers went, well if that works, it will work on building too.
34:28And that's how we get the reinforced concrete that we use to this day.
34:33So embedded into the concrete of the bridge is a steel mesh known as a rebar.
34:39That has a disadvantage, because of course metal corrodes, and as water penetrates concrete,
34:46so it comes into contact with the metal within it.
34:50The metal starts to rust, the metal starts to expand, the expansion cracks the concrete, which then emits more water,
35:00and as a result you end up with a situation in which, although the builded bridge may look strong from the outside,
35:07it's in fact literally rotting from within.
35:10Yeah, which metal have you just spray, William?
35:12So Rory's team has to check that the rebar is sound.
35:16We're inspecting the rebar to make sure it's not corroded, and then we're spraying concrete back in to give the deck back that strength.
35:23The problem is, the bridge needs to stay open to traffic, so the inspection needs to take place from below.
35:33In the dark, cramped confines of the secret world below the bridge,
35:38Steve the foreman is preparing his guys to strip the concrete off the deck to reveal the rebars.
35:44A few pins just remove the cot in there, these smaller patches, north, south sides of the beams, plus the underside.
35:53Right, no worries.
35:54Well, yeah, no worries then.
35:56Cheers.
36:00Using jackhammers to remove the concrete can cause fractures,
36:03so the team will blast the concrete away with a process called hydro demolition.
36:08They're blasting the concrete out with high pressure water, very powerful.
36:13If you don't know what you're doing in the wrong hands, it's lethal.
36:16The jets are 30 times more powerful than a garden hose,
36:20enough force to strip the skin off your bones,
36:23which is why they follow strict safety procedures.
36:27Let me know when you're ready.
36:29Ready whenever.
36:30Tell me you're ready, turn the water on, turn the water on now.
36:33OK, go turn it on now, mate.
36:38He's turning the rig on.
36:43And I turn the power up to 1100,
36:46and that's when he starts blasting the concrete for the hydrogen.
36:53The high pressure water isn't the only hazard facing the team.
36:57Because we're working over the live railway station,
36:59we need to contain all those thousands of litres of water
37:02that we're shooting at the deck.
37:04The whole area is enclosed in polythene sheeting.
37:08That results in a very dark and confined area that the guys are working in.
37:14It almost feels like you're pot hauling.
37:19Small areas that you've got to get around in.
37:23All you can see is water and concrete coming back in here, isn't you?
37:26You've got to really keep your wits about here.
37:32It's tight and it's difficult, but we'll just get on with it like, yeah.
37:38But all that water has to go somewhere.
37:42Steve is checking on the filtration system that siphons all that water away.
37:47No water here means we've got to build up in there,
37:50and that excess build up then will just overflow.
37:54That'll then start feeding back into the main drains.
37:57And that is something that we don't want on this job.
38:00Keeping all of this chemically contaminated water out of the drains
38:04is a crucial part of the process.
38:07You really don't want any contaminants going into the air, into the waterways.
38:12It has to go through a system where it's filtrated, cleaned, cleaned and cleaned again.
38:20That's not looking too bad at the moment.
38:23I'm quite happy with that.
38:26Satisfied that the filters are working,
38:29Steve heads back down to check on the job.
38:32Have a look. I've cleaned all that out.
38:34I think it should be OK.
38:36Go ahead, old bud.
38:38Check that out.
38:39Once the cutting's been removed, we then go in, inspect the area.
38:44Yeah, top down, Sean, that'll do, mate.
38:46Thank you. That's good, that.
38:48That area now is good enough for me to pass off.
38:51Very well then, Sean, I'll leave you to it.
38:53I'm out of here, mate, yeah?
38:54Use the shelf once you've finished.
38:56All right, come in, no worries, Steve.
38:58No worries.
39:00Electric anodes are put in place to help protect the steel
39:03before applying a fresh layer of concrete.
39:06But concreting above your head is far from simple.
39:10So Tomas and his team spray on the concrete
39:13in a process called shock-creating.
39:15Spray concrete is a difficult job because it's dirty, it's dusty,
39:20you have to work in a very harsh environment.
39:23It's a really challenging job, but, yeah, well managed.
39:27Ian, Steve, when you start, turn the feet down, mate.
39:29Tomas's team spray concrete at four times the speed of the firefighter's hose onto the rebars.
39:50It's difficult material to work with, it's a difficult environment,
39:53but at the end of the day it gives us a lot of advantages that pourable concrete would not allow us.
40:01Once the spraying is done, they scrape off the excess concrete,
40:05then smooth it down with a trowel.
40:08It's going to last for the next 50 years, yeah?
40:11The refurbishment team has been working 24-7 in a massive maze of scaffolding for more than two years.
40:23Identifying the weak spots, reinforcing the structure, and making it fit for the 21st century.
40:31Now the final stage of the project can begin.
40:37Installing the restored cast iron work that will leave the bridge looking like it's still 1896.
40:44Now it's in place, and that'll be the final sort of fixing place for that.
40:49Good job.
40:51Painter Ian Webster can now add the finishing touches.
40:56I'm about to apply a gold finish coat on the steel.
40:59It's already been blasted, primed, undercoat, then you just add the finished coat.
41:08It's not quite on the same scale as painting the fourth bridge, but it's still a lot of work.
41:14It's actually two to three years' work.
41:18It's a really big job. It's a big bridge.
41:2130,000 square metres to be exact.
41:24In 1897, the bridge would have been painted with lead-based paints.
41:30Lead paint was used everywhere in the Victorian era because it was so useful, it was so practical, it was so hard-wearing, it was so easy to paint with.
41:40And so it's used on buildings, it's used on toys.
41:44Adding lead into paint creates a paint which is slightly flexible.
41:49So if you coat iron with a nice thick coat of this lead paint, as it expands and contracts, the paint doesn't crack, and so it forms a really, really good layer of protection against corrosion.
42:00But lead has a downside.
42:04They didn't realise it was incredibly toxic, so that meant that it caused things like behavioural problems, it caused seizures, it stopped brain growth in children.
42:14It was dangerous, it could even kill you.
42:16Today, Ian is matching the original Victorian scheme with a modern, zinc-based, all-weather paint, designed to withstand the extremes of the Scottish climate.
42:27The reason we use this type of paint is because the lifespan is 25 years, and it's for the environment, and all different types of weather, like the cold, rain, snow.
42:38And because of the cold Scottish weather, Ian has to use heaters to keep the steel warm enough to apply the paint.
42:46We've got two heaters, one on each side.
42:49If we didn't do this, the paint wouldn't attach to the steel.
42:53It would sort of fall off, basically.
42:55Ian, like so many who work on this bridge, is blown away by the ingenuity and craftsmanship of the men who made it happen.
43:03The Victorians, the way they've built their bridges a hundred years ago, just amazing.
43:09I think if the Victorians were here now, they would feel incredibly proud of what they've built, and how well it stood up throughout its design life.
43:16There's still more to be done.
43:19A permanent access platform is being installed to help maintain the bridge in the future.
43:23And it will take at least another year before the project is complete, as the team maintains the groundbreaking work started by the original bridge builders more than a century ago.
43:37If they could see us now, they'd be proud of what we're doing, using these technologies that are emerging and the existing technologies to make sure that the bridge will have another 120 years' life.
43:47A permanent access platform is being built on our way.
43:50We'll be right there.
43:52And we'll be right back.
43:54If I can see us next week, we'll be right back.
43:57And I'm gonna stay safe.
44:02I can see you next week.